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  • Advances in Mathematical Physics
    09:00 -13:45
    2022-08-01-2022-08-01
    1 Oxford Street, Cambridge MA 02138
    Elliott-Lieb-conference-2022_banner-2-1536x734

    A Conference in Honor of Elliott H. Lieb on his 90th Birthday

    On July 30 – Aug 1, 2022 the Harvard Mathematics Department and the CMSA co-hosted a birthday conference in honor of Elliott Lieb.

    This meeting highlights Elliott’s vast contribution to math and physics. Additionally, this meeting features Prof. Lieb’s more recent impact in strong subadditivity of entropy and integrable systems (ice model, Temperley-Lieb algebra etc.).

    Venue:

    July 30–31, 2022: Hall B, Science Center, 1 Oxford Street, Cambridge, MA, 02138
    August 1, 2022: Hall C, Science Center, 1 Oxford Street, Cambridge, MA, 02138

    Schedule (pdf)

    Organizers:
    Michael Aizenman, Princeton University
    Joel Lebowitz, Rutgers University
    Ruedi Seiler, Technische Universität Berlin
    Herbert Spohn, Technical University of Munich
    Horng-Tzer Yau, Harvard University
    Shing-Tung Yau, Harvard University
    Jakob Yngvason, University of Vienna

    SPEAKERS:
    Rafael Benguria, Pontificia Universidad Catolica de Chile
    Eric Carlen, Rutgers University
    Philippe Di Francesco, University of Illinois
    Hugo Duminil-Copin, IHES
    László Erdös, Institute of Science and Technology Austria
    Rupert Frank, Ludwig Maximilian University of Munich
    Jürg Fröhlich, ETH Zurich
    Alessandro Giuliani, Università degli Studi Roma Tre
    Bertrand Halperin, Harvard University
    Klaus Hepp, Institute for Theoretical Physics, ETH Zurich
    Sabine Jansen, Ludwig Maximilian University of Munich
    Mathieu Lewin, Université Paris-Dauphine
    Bruno Nachtergaele, The University of California, Davis
    Yoshiko Ogata, University of Tokyo
    Ron Peled, Tel Aviv University
    Benjamin Schlein, University of Zurich
    Robert Seiringer, Institute of Science and Technology Austria
    Jan Philip Solovej, University of Copenhagen
    Hal Tasaki, Gakushuin University
    Simone Warzel, Technical University of Munich
    Jun Yin, The University of California, Los Angeles

     

    Elliott-Lieb-conference

2
  • Phase Transitions and Topological Defects in the Early Universe
    09:00 -17:00
    2022-08-02-2022-08-05
    CMSA, 20 Garden Street, Cambridge, MA 02138 USA
    Phase-Transitions_banner-1536x407-1

    On August 2–5, the CMSA hosted a workshop on Phase Transitions and Topological Defects in the Early Universe.

    The workshop was held in room G10 of the CMSA, located at 20 Garden Street, Cambridge, MA and online via Zoom webinar.

    The next decade will see a wealth of new cosmological data, which can lead to new insights into fundamental physics. Upcoming facilities (such as LISA) will be able to probe signals of fascinating phenomena in the early universe. These include signals from “Phase Transitions and Topological Defects,” which are ubiquitously given rise to in well-motivated UV models. In-depth studies of such signals requires cross-talks between experts from a wide spectrum of fields.

    The workshop aims to provide a platform for efficient exchange of new ideas related to these topics. It will start with an overview of some of the past and future experimental efforts. Next, there will be a substantial number of talks probing different aspects of phenomenology of phase transitions and topological defects in the early universe. It will finally close with discussions on recent formal development in the field.

    Scientific Advisory: Julian B. Muñoz, Lisa Randall, Matthew Reece, Tracy Slatyer, Shing-Tung Yau

    Organizers:
    Harvard: Nick DePorzio, Katie Fraser, Sam Homiller, Rashmish Mishra, & Aditya Parikh
    MIT: Pouya Asadi, Marianne Moore, & Yitian Sun

    Schedule/Format
    There will be 20+ 10 minute talks, ample discussion time, and lightning chalkboard talks.

    Speakers:

    • Nancy Aggarwal (Northwestern)
    • Jae Hyeok Chang (UMD – JHU)
    • Yanou Cui (UC Riverside)
    • David Dunsky (UC Berkeley)
    • Isabel Garcia-Garcia (KITP – UCSB)
    • Oliver Gould (Nottingham)
    • Yann Gouttenoire (Tel Aviv)
    • Eleanor Hall (UC Berkeley)
    • Sungwoo Hong (Chicago)
    • Anson Hook (UMD)
    • Jessica Howard (UC Irvine)
    • Seth Koren (Chicago)
    • Mrunal Korwar (Wisconsin)
    • Soubhik Kumar (UC Berkeley)
    • Vuk Mandic (Minnesota)
    • Yuto Minami (Osaka)
    • Michael Nee (Oxford)
    • Kai Schmitz (CERN)
    • Stephen R. Taylor (Vanderbilt)
    • Ofri Telem (UC Berkeley)
    • Juven Wang (Harvard)
    • Yikun Wang (Caltech)

    Participants:

    • Manuel Buen Abad (UMD)
    • Pouya Asadi (MIT)
    • Sean Benevedes (MIT)
    • Sandipan Bhattacherjee (Birla Institute of Technology Mesra Ranchi India)
    • Xingang Chen (Harvard University)
    • Nicholas DePorzio (Harvard University)
    • Peizhi Du (Stony Brook University)
    • Nicolas Fernandez (University of Illinois Urbana-Champaign)
    • Joshua Foster (MIT)
    • Katherine Fraser (Harvard University)
    • Sarah Geller (MIT)
    • Aurora Ireland (University of Chicago)
    • Marius Kongsore (New York University)
    • Ho Tat Lam (Massachusetts Institute of Technology)
    • Lingfeng Li (Brown University)
    • Yingying Li (Fermilab)
    • Gustavo Marques-Tavares (UMD)
    • Rashmish Mishra (Harvard University)
    • Siddharth Mishra-Sharma (MIT/Harvard University)
    • Toby Opferkuch (UC Berkeley)
    • Tong Ou (University of Chicago)
    • Aditya Parikh (Harvard University)
    • Yitian Sun (MIT)
    • Juan Sebastian Valbuena-Bermudez (Ludwig Maximilian University of Munich and Max Planck Institute for Physics)
    • Isaac Wang (Rutgers)
    • Wei Xue (University of Florida)
    • Winston Yin (UC Berkeley)
    • Quratulain Zahoor (The Islamia University of Bahwalpur Punjab (Pakistan)

    Schedule

    Tuesday, August 2, 2022

    9:00–9:20 amBreakfast
    9:20–9:30 amRashmish MishraOpening Remarks
    9:30–10:00 amVuk MandicTitle: Searching for the Stochastic Gravitational Wave Background with LISA

    Abstract: The upcoming space-borne gravitational wave detector Laser Interferometer Space Antenna (LISA) will open a window into the milliHertz band of the gravitational wave spectrum. Among the many sources in this band is the stochastic gravitational wave background (SGWB), arising as an incoherent superposition of many uncorrelated gravitational wave sources. The SGWB could be of cosmological origin, carrying unique information about the physical processes that took place within the first minute after the big bang, including possible phase transitions and topological defects. LISA therefore has the potential to illuminate particle physics at very high energy scales that may be inaccessible in laboratories. I will discuss how LISA can be used to search for the SGWB, highlighting a new pipeline developed for this purpose as well as several challenges and limitations that such a search will encounter.

    10:00–10:30 amNancy AggarwalTitle: Gravitational waves at frequencies above 10 kHz

    Abstract: Gravitational waves (GWs) at frequencies higher than the LIGO band can bring us completely new information about the universe. Besides being the most-interesting frequency region for looking at cosmological phenomena, they can also convey signatures of ultralight bosons through blackhole superradiance and light primordial blackholes (PBHs). I will introduce a new global initiative to study GW sources and detectors at ultra-high-frequencies (MHz-GHz), as well as a new experiment at Northwestern University to look for GWs in the frequency band of 10 kHz to 300 kHz using levitated optomechanical sensors. I will summarize the design, the current experimental progress, as well as a path forward for future improvements.

    10:30–11:00 amYuto MinamiTitle: New measurements of the cosmic birefringence

    Abstract: Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation I report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite released in 2018. The statistical significance of the measured signal is 2.4 sigma. Recently, we found a signal with 3.3 sigma statistical significance when we use the latest Planck data and consider an effect of polarised foreground emission. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

    11:00–1:30 pmBreak
    1:30–3:00 pmLighting Talks 1Lingfeng Li
    Winston Yin
    Marius Kongsore
    Nick DePorzio
    3:00–3:30 pmJae Hyeok ChangTitle: Correlating gravitational wave and gamma-ray signals from primordial black holes

    Abstract: Asteroid-mass primordial black holes (PBHs) can explain the observed dark matter abundance while being consistent with the current indirect detection constraints. These PBHs can produce gamma-ray signals from Hawking radiation that are within the sensitivity of future measurements by the AMEGO and e-ASTROGAM experiments. PBHs which give rise to such observable gamma-ray signals have a cosmic origin from large primordial curvature fluctuations. There must then be a companion, stochastic gravitational wave (GW) background produced by the same curvature fluctuations. I will demonstrate that the resulting GW signals will be well within the sensitivity of future detectors such as LISA, DECIGO, BBO, and the Einstein Telescope. The multimessenger signal from the observed gamma-rays and GWs will allow a precise measurement of the primordial curvature perturbation that produces the PBH. I will also argue that the resulting correlation between the two types of observations can provide a smoking-gun signal of PBHs.

    3:30–4:00 pmAnson Hook
    (Virtual via Zoom)
    Title: Early Universe Cosmology from Stochastic Gravitational Waves

    Abstract:  The causal tail of stochastic gravitational waves can be used to probe the energy density in free streaming relativistic species as well as measure gstar and beta functions as a function of temperature. In the event of the discovery of loud stochastic gravitational waves, we demonstrate that LISA can measure the free streaming fraction of the universe down to the 10^-3 level, 100 times more sensitive than current constraints. Additionally, it would be sensitive to O(1) deviations of gstar and the QCD beta function from their Standard Model value at temperatures ~ 10^5 GeV. In this case, many motivated models such as split SUSY and other solutions to the Electroweak Hierarchy problem would be tested. Future detectors, such as DECIGO, would be 100 times more sensitive than LISA to these effects and be capable of testing other motivated scenarios such as WIMPs and axions. The amazing prospect of using precision gravitational wave measurements to test such well motivated theories provides a benchmark to aim for when developing a precise understanding of the gravitational wave spectrum both experimentally and theoretically.

     

    Wednesday, August 3, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amKai Schmitz
    (Virtual via Zoom)
    Title: Gravitational waves from metastable cosmic strings

    Abstract: Cosmic strings are predicted by many Standard Model extensions involving the cosmological breaking of an Abelian symmetry and represent a potential source of primordial gravitational waves (GWs). In many Grand Unified Theories (GUTs), cosmic strings especially turn out to be metastable, as the nucleation of GUT monopoles along strings after a finite lifetime eventually leads to the collapse of the entire string network. In this talk, I will discuss the theoretical description of such a network and its individual components as well as the consequences for the emitted GW spectrum. Remarkably, the GW signal from metastable strings may well explain the common-spectrum process recently observed in pulsar timing data, while at the same time and in contrast to stable cosmic strings predicting a signal at higher frequencies that is still within the reach of current-generation ground-based interferometers. On their way to design sensitivity, existing GW experiments will thus have a realistic chance to probe particle physics processes at energies close to the GUT scale via the observation of GWs from metastable strings. This talk is based on 2107.04578 in collaboration with Wilfried Buchmüller and Valerie Domcke.

    10:00–10:30 amOliver Gould
    (Virtual via Zoom)
    Title: Effective field theory for cosmological phase transitions

    Abstract: Phase transitions are driven by thermal loop fluctuations, which modify background fields at leading order. This breaks the loop expansion and leads to large theoretical uncertainties in typical calculations, especially for gravitational wave predictions. I will give an overview of our present understanding of these uncertainties, and of the tools that have been developed to overcome them. Effective field theory has been at the forefront of this development, and I will outline how it can be used to solve a number of decades-long-standing theoretical problems.

    10:30–11:00 amIsabel Garcia-GarciaTitle: The Rocket Science of Expanding Bubbles
    11:00–1:30 pmBreak
    1:30–3:00 pmLightning Talks 2Sarah Geller
    Peizhi Du
    Tong Ou
    Isaac Wang
    Katie Fraser
    3:00–3:30 pmDavid Dunsky
    (Virtual via Zoom)
    Title: Gravitational Wave Gastronomy

    Abstract: The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational wave fingerprints. In this talk, I will discuss the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and “eat” the strings, 2) the collapse and decay of a monopole-string network by strings that “eat” the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and “eat” the wall, and 4) the collapse and decay of a string-bounded wall network by walls that “eat” the strings. We call the gravitational wave signals produced from the “eating” of one topological defect by another “gravitational wave gastronomy”. The gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO(10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects.

    3:30–4:00 pmYanou Cui
    (Virtual via Zoom)
    Title: Cosmic Archaeology with gravitational waves from (axion) cosmic strings

    Abstract: In this talk I will discuss important aspects of cosmology and particle physics that can be probed with GW signals from cosmic strings: probing the pre-BBN primordial dark age and axion physics.  Gravitational waves (GWs) originating from the dynamics of a cosmic string network have the ability to probe many otherwise inaccessible properties of the early universe. In particular, I will discuss how the frequency spectrum of a stochastic GW background (SGWB) from a cosmic string network can be used to probe Hubble expansion rate of the early universe prior to Big Bang Nucleosynthesis (BBN), during the “primordial dark age”. Furthermore I will show that in contrast to the standard expectation, cosmic strings formed before inflation could regrow back into the horizon and leave imprints, with GW bursts potentially being the leading signal. In relation to axion physics I will also demonstrate the detection prospect for SGWB from global/axion strings which may provide a new probe for axion-like dark matter models, considering various scenarios of cosmic history.

    4:00–4:30 pmMichael NeeTitle: The Boring Monopole

    Abstract: First order phase transitions play an important role in the cosmology of many theories of BSM physics. In this talk I will discuss how a population of magnetic monopoles present in the early universe can seed first order phase transitions, causing them to proceed much more rapidly than in the usual case. The field profiles describing the decay do not have the typically assumed O(3)/O(4) symmetry, thus requiring an extension of the usual decay rate calculation. To numerically determine the saddle point solutions which describe the decay we use a new algorithm based on the mountain pass theorem. Our results show that monopole-catalysed tunnelling can dominate over the homogeneous decay for a wide range of parameters.

     

    Thursday, August 4, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amYikun WangTitle: A New Approach to Electroweak Symmetry Non-Restoration

    Abstract: Electroweak symmetry non-restoration up to high temperatures well above the electroweak scale has intriguing implications for (electroweak) baryogenesis and early universe thermal histories. In this talk, I will discuss such a possible fate of the electroweak symmetry in the early universe and a new approach to realize it, via an inert Higgs sector that couples to the Standard Model Higgs as well as an extended scalar singlet sector. Examples of benchmark scenarios that allow for electroweak symmetry non-restoration all the way up to hundreds of TeV temperatures, at the same time featuring suppressed sphaleron washout factors down to the electroweak scale, will be presented. Renormalization group improvements and thermal resummation, necessary to evaluate the effective potential spanning over a broad range of energy scales and temperatures, have been implemented calculating the thermal history. This method for transmitting the Standard Model broken electroweak symmetry to an inert Higgs sector can be scrutinized through Higgs physics phenomenology and electroweak precision measurements at the HL-LHC.

    10:00–10:30 amSoubhik KumarTitle: Probing primordial fluctuations through stochastic gravitational wave background anisotropies

    Abstract: Stochastic gravitational wave backgrounds are expected to be anisotropic. While such anisotropies can be of astrophysical origin, a cosmological component of such anisotropies can carry rich information about primordial perturbations. Focusing on the case of a cosmological phase transition, I will talk about how such anisotropies can give us a powerful probe of primordial non-Gaussianities, complementary to current and future CMB and LSS searches. In the scenario where astrophysical foregrounds are also present, I will then discuss some strategies using which we can extract the cosmological signal, focusing on the case of LISA, Taiji and BBO, in particular.

    10:30–11:00 amJessica Howard
    (Virtual via Zoom)
    Title: Dark Matter Freeze-out during SU(2)_L Confinement

    Abstract: We explore the possibility that dark matter is a pair of SU(2)_L doublets and propose a novel mechanism of dark matter production that proceeds through the confinement of the weak sector of the Standard Model. This phase of confinement causes the Standard Model doublets and dark matter to confine into pion-like objects. Before the weak sector deconfines, the dark pions freezeout and generate a relic abundance of dark matter. We solve the Boltzmann equations for this scenario to determine the scale of confinement and constituent dark matter mass required to produce the observed relic density. We determine which regions of this parameter space evade direct detection and collider bounds.

    11:00–11:30 amJuven WangTitle: Quantum Matter Adventure to Beyond the Standard Model Prediction

    Abstract: Ideas developed from the quantum matter and quantum field theory frontier may guide us to explore new physics beyond the 4d Standard Model. I propose a few such ideas. First, new physics for neutrinos: right-handed neutrinos carry a Z_{16} class mixed gauge-gravitational global anomaly index, which could be replaced by 4d or 5d topological quantum field theory, or 4d interacting conformal field theory. These theories provide possible new neutrino mass mechanisms [arXiv:2012.15860]. Second, deconfined quantum criticality between Grand Unified Theories: dictated by a Z_2 class global anomaly, a gapless quantum critical region can happen between Georgi-Glashow and Pati-Salam models as deformation of the Standard Model, where Beyond the Standard Model physics and Dark Gauge sector occur as neighbor phases [arXiv:2106.16248, arXiv:2112.14765, arXiv:2204.08393]. Third, the Strong CP problem can be solved by a new solution involving Symmetric Mass Generation [arXiv:2204.14271].

    11:30–1:30 pmBreak
    1:30–4:00 pmStephen R. TaylorTitle: Pulsar Timing Arrays: The Next Window onto the Low-frequency Gravitational-wave Universe

    Abstract: The nanohertz-frequency band of gravitational waves should be awash with signals from supermassive black-hole binaries, as well as cosmological signatures of phase transitions, cosmic strings, and other relics of the early Universe. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav) and the International Pulsar Timing Array are poised to chart this new frontier of gravitational wave discovery within the next several years. I will present exciting new results from recent cutting-edge searches, discuss some milestones on the road to the next decade of PTA discovery, and take workshop attendees through a guided tutorial of how the broader community can use our production-level analysis pipeline to extract new science with ease.

     

    Friday, August 5, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amOfri TelemTitle: Charge-Monopole Pairwise Phases from Dressed Quantum States
    10:00–10:30 amSungwoo HongTitle: Coupling a Cosmic String to a TQFT

    Abstract: In the last few years, the notion of symmetry has been enlarged to “generalized symmetry” or “higher-form symmetry” and these more generalized symmetries have played a critical role in deepening our understanding of QFT, notably IR phases of QFT. In this talk, I will discuss a various ways of coupling the axion-Maxwell theory to a topological field theory (TQFT). Contrary to a common wisdom, I will show that such topological modifications can lead to direct changes in the local physics with possible observable consequences. This surprise can be realized by a dimensional reduction, namely, a coupling to a TQFT in 4d leads to a non-trivial and local impact on the 2d string world-sheet QFT. There also exists a topological modification of the theory, i.e. gauging a discrete subgroup of 0-form shift symmetry, and this time it results in a alteration of spectrum of cosmic strings. If time permits, I will also discuss generalized symmetries and associated higher-groups of these theories.

    10:30–11:00 amEleanor Hall
    (Virtual via Zoom)
    Title: Non-perturbative methods for false vacuum decay

    Abstract: Gravitational waves from phase transitions in the early universe are one of our most promising signal channels of BSM physics; however, existing methods for predicting these signals are limited to weakly-coupled theories. In this talk, I present the quasi-stationary effective action, a new non-perturbative formalism for false vacuum decay that integrates over local fluctuations in field space using the functional renormalization group. This method opens the door to reliable calculation of gravitational wave signals and false vacuum decay rates for strongly-interacting theories. I will also discuss recent developments and ongoing extensions of the QSEA.

    11:00–1:30 pmBreak
    1:30–2:00 pmMrunal KorwarTitle: Electroweak Symmetric Balls

    Abstract: Electroweak symmetric balls are macroscopic objects with electroweak symmetry restored inside. Such an object can arise in models where dark sectors contain monopole or non-topological soliton with a Higgs portal interaction to the Standard Model. It could be produced in the early universe via phase transition or parametric resonance, accounting for all dark matter. In a scenario where the balls are allowed to evaporate, the observed baryon asymmetry in our universe could be explained by a mechanism of “catalyzed baryogenesis.” In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions via electroweak Sphaleron. Because of electroweak symmetric cores, such objects have a large geometric cross-section off a nucleus, generating a multi-hit signature in large volume detectors. These objects could radiatively capture a nucleus and release GeV-scale energy for each interaction. The IceCube detector can probe dark matter balls with masses up to a gram.

    2:00–2:30 pmSeth KorenTitle: Discrete Gauged Baryon Minus Lepton Number and the Cosmological Lithium Problem

    Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.
    The cosmological lithium problem—that theory predicts a primordial abundance thrice as high as that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

    2:30–3:00 pmYann GouttenoireTitle: Supercool Composite Dark Matter beyond 100 TeV

     

    Phase-Transitions_Poster

3
  • Phase Transitions and Topological Defects in the Early Universe
    09:00 -17:00
    2022-08-03-2022-08-05
    CMSA, 20 Garden Street, Cambridge, MA 02138 USA
    Phase-Transitions_banner-1536x407-1

    On August 2–5, the CMSA hosted a workshop on Phase Transitions and Topological Defects in the Early Universe.

    The workshop was held in room G10 of the CMSA, located at 20 Garden Street, Cambridge, MA and online via Zoom webinar.

    The next decade will see a wealth of new cosmological data, which can lead to new insights into fundamental physics. Upcoming facilities (such as LISA) will be able to probe signals of fascinating phenomena in the early universe. These include signals from “Phase Transitions and Topological Defects,” which are ubiquitously given rise to in well-motivated UV models. In-depth studies of such signals requires cross-talks between experts from a wide spectrum of fields.

    The workshop aims to provide a platform for efficient exchange of new ideas related to these topics. It will start with an overview of some of the past and future experimental efforts. Next, there will be a substantial number of talks probing different aspects of phenomenology of phase transitions and topological defects in the early universe. It will finally close with discussions on recent formal development in the field.

    Scientific Advisory: Julian B. Muñoz, Lisa Randall, Matthew Reece, Tracy Slatyer, Shing-Tung Yau

    Organizers:
    Harvard: Nick DePorzio, Katie Fraser, Sam Homiller, Rashmish Mishra, & Aditya Parikh
    MIT: Pouya Asadi, Marianne Moore, & Yitian Sun

    Schedule/Format
    There will be 20+ 10 minute talks, ample discussion time, and lightning chalkboard talks.

    Speakers:

    • Nancy Aggarwal (Northwestern)
    • Jae Hyeok Chang (UMD – JHU)
    • Yanou Cui (UC Riverside)
    • David Dunsky (UC Berkeley)
    • Isabel Garcia-Garcia (KITP – UCSB)
    • Oliver Gould (Nottingham)
    • Yann Gouttenoire (Tel Aviv)
    • Eleanor Hall (UC Berkeley)
    • Sungwoo Hong (Chicago)
    • Anson Hook (UMD)
    • Jessica Howard (UC Irvine)
    • Seth Koren (Chicago)
    • Mrunal Korwar (Wisconsin)
    • Soubhik Kumar (UC Berkeley)
    • Vuk Mandic (Minnesota)
    • Yuto Minami (Osaka)
    • Michael Nee (Oxford)
    • Kai Schmitz (CERN)
    • Stephen R. Taylor (Vanderbilt)
    • Ofri Telem (UC Berkeley)
    • Juven Wang (Harvard)
    • Yikun Wang (Caltech)

    Participants:

    • Manuel Buen Abad (UMD)
    • Pouya Asadi (MIT)
    • Sean Benevedes (MIT)
    • Sandipan Bhattacherjee (Birla Institute of Technology Mesra Ranchi India)
    • Xingang Chen (Harvard University)
    • Nicholas DePorzio (Harvard University)
    • Peizhi Du (Stony Brook University)
    • Nicolas Fernandez (University of Illinois Urbana-Champaign)
    • Joshua Foster (MIT)
    • Katherine Fraser (Harvard University)
    • Sarah Geller (MIT)
    • Aurora Ireland (University of Chicago)
    • Marius Kongsore (New York University)
    • Ho Tat Lam (Massachusetts Institute of Technology)
    • Lingfeng Li (Brown University)
    • Yingying Li (Fermilab)
    • Gustavo Marques-Tavares (UMD)
    • Rashmish Mishra (Harvard University)
    • Siddharth Mishra-Sharma (MIT/Harvard University)
    • Toby Opferkuch (UC Berkeley)
    • Tong Ou (University of Chicago)
    • Aditya Parikh (Harvard University)
    • Yitian Sun (MIT)
    • Juan Sebastian Valbuena-Bermudez (Ludwig Maximilian University of Munich and Max Planck Institute for Physics)
    • Isaac Wang (Rutgers)
    • Wei Xue (University of Florida)
    • Winston Yin (UC Berkeley)
    • Quratulain Zahoor (The Islamia University of Bahwalpur Punjab (Pakistan)

    Schedule

    Tuesday, August 2, 2022

    9:00–9:20 amBreakfast
    9:20–9:30 amRashmish MishraOpening Remarks
    9:30–10:00 amVuk MandicTitle: Searching for the Stochastic Gravitational Wave Background with LISA

    Abstract: The upcoming space-borne gravitational wave detector Laser Interferometer Space Antenna (LISA) will open a window into the milliHertz band of the gravitational wave spectrum. Among the many sources in this band is the stochastic gravitational wave background (SGWB), arising as an incoherent superposition of many uncorrelated gravitational wave sources. The SGWB could be of cosmological origin, carrying unique information about the physical processes that took place within the first minute after the big bang, including possible phase transitions and topological defects. LISA therefore has the potential to illuminate particle physics at very high energy scales that may be inaccessible in laboratories. I will discuss how LISA can be used to search for the SGWB, highlighting a new pipeline developed for this purpose as well as several challenges and limitations that such a search will encounter.

    10:00–10:30 amNancy AggarwalTitle: Gravitational waves at frequencies above 10 kHz

    Abstract: Gravitational waves (GWs) at frequencies higher than the LIGO band can bring us completely new information about the universe. Besides being the most-interesting frequency region for looking at cosmological phenomena, they can also convey signatures of ultralight bosons through blackhole superradiance and light primordial blackholes (PBHs). I will introduce a new global initiative to study GW sources and detectors at ultra-high-frequencies (MHz-GHz), as well as a new experiment at Northwestern University to look for GWs in the frequency band of 10 kHz to 300 kHz using levitated optomechanical sensors. I will summarize the design, the current experimental progress, as well as a path forward for future improvements.

    10:30–11:00 amYuto MinamiTitle: New measurements of the cosmic birefringence

    Abstract: Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation I report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite released in 2018. The statistical significance of the measured signal is 2.4 sigma. Recently, we found a signal with 3.3 sigma statistical significance when we use the latest Planck data and consider an effect of polarised foreground emission. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

    11:00–1:30 pmBreak
    1:30–3:00 pmLighting Talks 1Lingfeng Li
    Winston Yin
    Marius Kongsore
    Nick DePorzio
    3:00–3:30 pmJae Hyeok ChangTitle: Correlating gravitational wave and gamma-ray signals from primordial black holes

    Abstract: Asteroid-mass primordial black holes (PBHs) can explain the observed dark matter abundance while being consistent with the current indirect detection constraints. These PBHs can produce gamma-ray signals from Hawking radiation that are within the sensitivity of future measurements by the AMEGO and e-ASTROGAM experiments. PBHs which give rise to such observable gamma-ray signals have a cosmic origin from large primordial curvature fluctuations. There must then be a companion, stochastic gravitational wave (GW) background produced by the same curvature fluctuations. I will demonstrate that the resulting GW signals will be well within the sensitivity of future detectors such as LISA, DECIGO, BBO, and the Einstein Telescope. The multimessenger signal from the observed gamma-rays and GWs will allow a precise measurement of the primordial curvature perturbation that produces the PBH. I will also argue that the resulting correlation between the two types of observations can provide a smoking-gun signal of PBHs.

    3:30–4:00 pmAnson Hook
    (Virtual via Zoom)
    Title: Early Universe Cosmology from Stochastic Gravitational Waves

    Abstract:  The causal tail of stochastic gravitational waves can be used to probe the energy density in free streaming relativistic species as well as measure gstar and beta functions as a function of temperature. In the event of the discovery of loud stochastic gravitational waves, we demonstrate that LISA can measure the free streaming fraction of the universe down to the 10^-3 level, 100 times more sensitive than current constraints. Additionally, it would be sensitive to O(1) deviations of gstar and the QCD beta function from their Standard Model value at temperatures ~ 10^5 GeV. In this case, many motivated models such as split SUSY and other solutions to the Electroweak Hierarchy problem would be tested. Future detectors, such as DECIGO, would be 100 times more sensitive than LISA to these effects and be capable of testing other motivated scenarios such as WIMPs and axions. The amazing prospect of using precision gravitational wave measurements to test such well motivated theories provides a benchmark to aim for when developing a precise understanding of the gravitational wave spectrum both experimentally and theoretically.

     

    Wednesday, August 3, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amKai Schmitz
    (Virtual via Zoom)
    Title: Gravitational waves from metastable cosmic strings

    Abstract: Cosmic strings are predicted by many Standard Model extensions involving the cosmological breaking of an Abelian symmetry and represent a potential source of primordial gravitational waves (GWs). In many Grand Unified Theories (GUTs), cosmic strings especially turn out to be metastable, as the nucleation of GUT monopoles along strings after a finite lifetime eventually leads to the collapse of the entire string network. In this talk, I will discuss the theoretical description of such a network and its individual components as well as the consequences for the emitted GW spectrum. Remarkably, the GW signal from metastable strings may well explain the common-spectrum process recently observed in pulsar timing data, while at the same time and in contrast to stable cosmic strings predicting a signal at higher frequencies that is still within the reach of current-generation ground-based interferometers. On their way to design sensitivity, existing GW experiments will thus have a realistic chance to probe particle physics processes at energies close to the GUT scale via the observation of GWs from metastable strings. This talk is based on 2107.04578 in collaboration with Wilfried Buchmüller and Valerie Domcke.

    10:00–10:30 amOliver Gould
    (Virtual via Zoom)
    Title: Effective field theory for cosmological phase transitions

    Abstract: Phase transitions are driven by thermal loop fluctuations, which modify background fields at leading order. This breaks the loop expansion and leads to large theoretical uncertainties in typical calculations, especially for gravitational wave predictions. I will give an overview of our present understanding of these uncertainties, and of the tools that have been developed to overcome them. Effective field theory has been at the forefront of this development, and I will outline how it can be used to solve a number of decades-long-standing theoretical problems.

    10:30–11:00 amIsabel Garcia-GarciaTitle: The Rocket Science of Expanding Bubbles
    11:00–1:30 pmBreak
    1:30–3:00 pmLightning Talks 2Sarah Geller
    Peizhi Du
    Tong Ou
    Isaac Wang
    Katie Fraser
    3:00–3:30 pmDavid Dunsky
    (Virtual via Zoom)
    Title: Gravitational Wave Gastronomy

    Abstract: The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational wave fingerprints. In this talk, I will discuss the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and “eat” the strings, 2) the collapse and decay of a monopole-string network by strings that “eat” the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and “eat” the wall, and 4) the collapse and decay of a string-bounded wall network by walls that “eat” the strings. We call the gravitational wave signals produced from the “eating” of one topological defect by another “gravitational wave gastronomy”. The gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO(10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects.

    3:30–4:00 pmYanou Cui
    (Virtual via Zoom)
    Title: Cosmic Archaeology with gravitational waves from (axion) cosmic strings

    Abstract: In this talk I will discuss important aspects of cosmology and particle physics that can be probed with GW signals from cosmic strings: probing the pre-BBN primordial dark age and axion physics.  Gravitational waves (GWs) originating from the dynamics of a cosmic string network have the ability to probe many otherwise inaccessible properties of the early universe. In particular, I will discuss how the frequency spectrum of a stochastic GW background (SGWB) from a cosmic string network can be used to probe Hubble expansion rate of the early universe prior to Big Bang Nucleosynthesis (BBN), during the “primordial dark age”. Furthermore I will show that in contrast to the standard expectation, cosmic strings formed before inflation could regrow back into the horizon and leave imprints, with GW bursts potentially being the leading signal. In relation to axion physics I will also demonstrate the detection prospect for SGWB from global/axion strings which may provide a new probe for axion-like dark matter models, considering various scenarios of cosmic history.

    4:00–4:30 pmMichael NeeTitle: The Boring Monopole

    Abstract: First order phase transitions play an important role in the cosmology of many theories of BSM physics. In this talk I will discuss how a population of magnetic monopoles present in the early universe can seed first order phase transitions, causing them to proceed much more rapidly than in the usual case. The field profiles describing the decay do not have the typically assumed O(3)/O(4) symmetry, thus requiring an extension of the usual decay rate calculation. To numerically determine the saddle point solutions which describe the decay we use a new algorithm based on the mountain pass theorem. Our results show that monopole-catalysed tunnelling can dominate over the homogeneous decay for a wide range of parameters.

     

    Thursday, August 4, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amYikun WangTitle: A New Approach to Electroweak Symmetry Non-Restoration

    Abstract: Electroweak symmetry non-restoration up to high temperatures well above the electroweak scale has intriguing implications for (electroweak) baryogenesis and early universe thermal histories. In this talk, I will discuss such a possible fate of the electroweak symmetry in the early universe and a new approach to realize it, via an inert Higgs sector that couples to the Standard Model Higgs as well as an extended scalar singlet sector. Examples of benchmark scenarios that allow for electroweak symmetry non-restoration all the way up to hundreds of TeV temperatures, at the same time featuring suppressed sphaleron washout factors down to the electroweak scale, will be presented. Renormalization group improvements and thermal resummation, necessary to evaluate the effective potential spanning over a broad range of energy scales and temperatures, have been implemented calculating the thermal history. This method for transmitting the Standard Model broken electroweak symmetry to an inert Higgs sector can be scrutinized through Higgs physics phenomenology and electroweak precision measurements at the HL-LHC.

    10:00–10:30 amSoubhik KumarTitle: Probing primordial fluctuations through stochastic gravitational wave background anisotropies

    Abstract: Stochastic gravitational wave backgrounds are expected to be anisotropic. While such anisotropies can be of astrophysical origin, a cosmological component of such anisotropies can carry rich information about primordial perturbations. Focusing on the case of a cosmological phase transition, I will talk about how such anisotropies can give us a powerful probe of primordial non-Gaussianities, complementary to current and future CMB and LSS searches. In the scenario where astrophysical foregrounds are also present, I will then discuss some strategies using which we can extract the cosmological signal, focusing on the case of LISA, Taiji and BBO, in particular.

    10:30–11:00 amJessica Howard
    (Virtual via Zoom)
    Title: Dark Matter Freeze-out during SU(2)_L Confinement

    Abstract: We explore the possibility that dark matter is a pair of SU(2)_L doublets and propose a novel mechanism of dark matter production that proceeds through the confinement of the weak sector of the Standard Model. This phase of confinement causes the Standard Model doublets and dark matter to confine into pion-like objects. Before the weak sector deconfines, the dark pions freezeout and generate a relic abundance of dark matter. We solve the Boltzmann equations for this scenario to determine the scale of confinement and constituent dark matter mass required to produce the observed relic density. We determine which regions of this parameter space evade direct detection and collider bounds.

    11:00–11:30 amJuven WangTitle: Quantum Matter Adventure to Beyond the Standard Model Prediction

    Abstract: Ideas developed from the quantum matter and quantum field theory frontier may guide us to explore new physics beyond the 4d Standard Model. I propose a few such ideas. First, new physics for neutrinos: right-handed neutrinos carry a Z_{16} class mixed gauge-gravitational global anomaly index, which could be replaced by 4d or 5d topological quantum field theory, or 4d interacting conformal field theory. These theories provide possible new neutrino mass mechanisms [arXiv:2012.15860]. Second, deconfined quantum criticality between Grand Unified Theories: dictated by a Z_2 class global anomaly, a gapless quantum critical region can happen between Georgi-Glashow and Pati-Salam models as deformation of the Standard Model, where Beyond the Standard Model physics and Dark Gauge sector occur as neighbor phases [arXiv:2106.16248, arXiv:2112.14765, arXiv:2204.08393]. Third, the Strong CP problem can be solved by a new solution involving Symmetric Mass Generation [arXiv:2204.14271].

    11:30–1:30 pmBreak
    1:30–4:00 pmStephen R. TaylorTitle: Pulsar Timing Arrays: The Next Window onto the Low-frequency Gravitational-wave Universe

    Abstract: The nanohertz-frequency band of gravitational waves should be awash with signals from supermassive black-hole binaries, as well as cosmological signatures of phase transitions, cosmic strings, and other relics of the early Universe. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav) and the International Pulsar Timing Array are poised to chart this new frontier of gravitational wave discovery within the next several years. I will present exciting new results from recent cutting-edge searches, discuss some milestones on the road to the next decade of PTA discovery, and take workshop attendees through a guided tutorial of how the broader community can use our production-level analysis pipeline to extract new science with ease.

     

    Friday, August 5, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amOfri TelemTitle: Charge-Monopole Pairwise Phases from Dressed Quantum States
    10:00–10:30 amSungwoo HongTitle: Coupling a Cosmic String to a TQFT

    Abstract: In the last few years, the notion of symmetry has been enlarged to “generalized symmetry” or “higher-form symmetry” and these more generalized symmetries have played a critical role in deepening our understanding of QFT, notably IR phases of QFT. In this talk, I will discuss a various ways of coupling the axion-Maxwell theory to a topological field theory (TQFT). Contrary to a common wisdom, I will show that such topological modifications can lead to direct changes in the local physics with possible observable consequences. This surprise can be realized by a dimensional reduction, namely, a coupling to a TQFT in 4d leads to a non-trivial and local impact on the 2d string world-sheet QFT. There also exists a topological modification of the theory, i.e. gauging a discrete subgroup of 0-form shift symmetry, and this time it results in a alteration of spectrum of cosmic strings. If time permits, I will also discuss generalized symmetries and associated higher-groups of these theories.

    10:30–11:00 amEleanor Hall
    (Virtual via Zoom)
    Title: Non-perturbative methods for false vacuum decay

    Abstract: Gravitational waves from phase transitions in the early universe are one of our most promising signal channels of BSM physics; however, existing methods for predicting these signals are limited to weakly-coupled theories. In this talk, I present the quasi-stationary effective action, a new non-perturbative formalism for false vacuum decay that integrates over local fluctuations in field space using the functional renormalization group. This method opens the door to reliable calculation of gravitational wave signals and false vacuum decay rates for strongly-interacting theories. I will also discuss recent developments and ongoing extensions of the QSEA.

    11:00–1:30 pmBreak
    1:30–2:00 pmMrunal KorwarTitle: Electroweak Symmetric Balls

    Abstract: Electroweak symmetric balls are macroscopic objects with electroweak symmetry restored inside. Such an object can arise in models where dark sectors contain monopole or non-topological soliton with a Higgs portal interaction to the Standard Model. It could be produced in the early universe via phase transition or parametric resonance, accounting for all dark matter. In a scenario where the balls are allowed to evaporate, the observed baryon asymmetry in our universe could be explained by a mechanism of “catalyzed baryogenesis.” In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions via electroweak Sphaleron. Because of electroweak symmetric cores, such objects have a large geometric cross-section off a nucleus, generating a multi-hit signature in large volume detectors. These objects could radiatively capture a nucleus and release GeV-scale energy for each interaction. The IceCube detector can probe dark matter balls with masses up to a gram.

    2:00–2:30 pmSeth KorenTitle: Discrete Gauged Baryon Minus Lepton Number and the Cosmological Lithium Problem

    Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.
    The cosmological lithium problem—that theory predicts a primordial abundance thrice as high as that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

    2:30–3:00 pmYann GouttenoireTitle: Supercool Composite Dark Matter beyond 100 TeV

     

    Phase-Transitions_Poster

4
  • Phase Transitions and Topological Defects in the Early Universe
    09:00 -17:00
    2022-08-04-2022-08-05
    CMSA, 20 Garden Street, Cambridge, MA 02138 USA
    Phase-Transitions_banner-1536x407-1

    On August 2–5, the CMSA hosted a workshop on Phase Transitions and Topological Defects in the Early Universe.

    The workshop was held in room G10 of the CMSA, located at 20 Garden Street, Cambridge, MA and online via Zoom webinar.

    The next decade will see a wealth of new cosmological data, which can lead to new insights into fundamental physics. Upcoming facilities (such as LISA) will be able to probe signals of fascinating phenomena in the early universe. These include signals from “Phase Transitions and Topological Defects,” which are ubiquitously given rise to in well-motivated UV models. In-depth studies of such signals requires cross-talks between experts from a wide spectrum of fields.

    The workshop aims to provide a platform for efficient exchange of new ideas related to these topics. It will start with an overview of some of the past and future experimental efforts. Next, there will be a substantial number of talks probing different aspects of phenomenology of phase transitions and topological defects in the early universe. It will finally close with discussions on recent formal development in the field.

    Scientific Advisory: Julian B. Muñoz, Lisa Randall, Matthew Reece, Tracy Slatyer, Shing-Tung Yau

    Organizers:
    Harvard: Nick DePorzio, Katie Fraser, Sam Homiller, Rashmish Mishra, & Aditya Parikh
    MIT: Pouya Asadi, Marianne Moore, & Yitian Sun

    Schedule/Format
    There will be 20+ 10 minute talks, ample discussion time, and lightning chalkboard talks.

    Speakers:

    • Nancy Aggarwal (Northwestern)
    • Jae Hyeok Chang (UMD – JHU)
    • Yanou Cui (UC Riverside)
    • David Dunsky (UC Berkeley)
    • Isabel Garcia-Garcia (KITP – UCSB)
    • Oliver Gould (Nottingham)
    • Yann Gouttenoire (Tel Aviv)
    • Eleanor Hall (UC Berkeley)
    • Sungwoo Hong (Chicago)
    • Anson Hook (UMD)
    • Jessica Howard (UC Irvine)
    • Seth Koren (Chicago)
    • Mrunal Korwar (Wisconsin)
    • Soubhik Kumar (UC Berkeley)
    • Vuk Mandic (Minnesota)
    • Yuto Minami (Osaka)
    • Michael Nee (Oxford)
    • Kai Schmitz (CERN)
    • Stephen R. Taylor (Vanderbilt)
    • Ofri Telem (UC Berkeley)
    • Juven Wang (Harvard)
    • Yikun Wang (Caltech)

    Participants:

    • Manuel Buen Abad (UMD)
    • Pouya Asadi (MIT)
    • Sean Benevedes (MIT)
    • Sandipan Bhattacherjee (Birla Institute of Technology Mesra Ranchi India)
    • Xingang Chen (Harvard University)
    • Nicholas DePorzio (Harvard University)
    • Peizhi Du (Stony Brook University)
    • Nicolas Fernandez (University of Illinois Urbana-Champaign)
    • Joshua Foster (MIT)
    • Katherine Fraser (Harvard University)
    • Sarah Geller (MIT)
    • Aurora Ireland (University of Chicago)
    • Marius Kongsore (New York University)
    • Ho Tat Lam (Massachusetts Institute of Technology)
    • Lingfeng Li (Brown University)
    • Yingying Li (Fermilab)
    • Gustavo Marques-Tavares (UMD)
    • Rashmish Mishra (Harvard University)
    • Siddharth Mishra-Sharma (MIT/Harvard University)
    • Toby Opferkuch (UC Berkeley)
    • Tong Ou (University of Chicago)
    • Aditya Parikh (Harvard University)
    • Yitian Sun (MIT)
    • Juan Sebastian Valbuena-Bermudez (Ludwig Maximilian University of Munich and Max Planck Institute for Physics)
    • Isaac Wang (Rutgers)
    • Wei Xue (University of Florida)
    • Winston Yin (UC Berkeley)
    • Quratulain Zahoor (The Islamia University of Bahwalpur Punjab (Pakistan)

    Schedule

    Tuesday, August 2, 2022

    9:00–9:20 amBreakfast
    9:20–9:30 amRashmish MishraOpening Remarks
    9:30–10:00 amVuk MandicTitle: Searching for the Stochastic Gravitational Wave Background with LISA

    Abstract: The upcoming space-borne gravitational wave detector Laser Interferometer Space Antenna (LISA) will open a window into the milliHertz band of the gravitational wave spectrum. Among the many sources in this band is the stochastic gravitational wave background (SGWB), arising as an incoherent superposition of many uncorrelated gravitational wave sources. The SGWB could be of cosmological origin, carrying unique information about the physical processes that took place within the first minute after the big bang, including possible phase transitions and topological defects. LISA therefore has the potential to illuminate particle physics at very high energy scales that may be inaccessible in laboratories. I will discuss how LISA can be used to search for the SGWB, highlighting a new pipeline developed for this purpose as well as several challenges and limitations that such a search will encounter.

    10:00–10:30 amNancy AggarwalTitle: Gravitational waves at frequencies above 10 kHz

    Abstract: Gravitational waves (GWs) at frequencies higher than the LIGO band can bring us completely new information about the universe. Besides being the most-interesting frequency region for looking at cosmological phenomena, they can also convey signatures of ultralight bosons through blackhole superradiance and light primordial blackholes (PBHs). I will introduce a new global initiative to study GW sources and detectors at ultra-high-frequencies (MHz-GHz), as well as a new experiment at Northwestern University to look for GWs in the frequency band of 10 kHz to 300 kHz using levitated optomechanical sensors. I will summarize the design, the current experimental progress, as well as a path forward for future improvements.

    10:30–11:00 amYuto MinamiTitle: New measurements of the cosmic birefringence

    Abstract: Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation I report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite released in 2018. The statistical significance of the measured signal is 2.4 sigma. Recently, we found a signal with 3.3 sigma statistical significance when we use the latest Planck data and consider an effect of polarised foreground emission. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

    11:00–1:30 pmBreak
    1:30–3:00 pmLighting Talks 1Lingfeng Li
    Winston Yin
    Marius Kongsore
    Nick DePorzio
    3:00–3:30 pmJae Hyeok ChangTitle: Correlating gravitational wave and gamma-ray signals from primordial black holes

    Abstract: Asteroid-mass primordial black holes (PBHs) can explain the observed dark matter abundance while being consistent with the current indirect detection constraints. These PBHs can produce gamma-ray signals from Hawking radiation that are within the sensitivity of future measurements by the AMEGO and e-ASTROGAM experiments. PBHs which give rise to such observable gamma-ray signals have a cosmic origin from large primordial curvature fluctuations. There must then be a companion, stochastic gravitational wave (GW) background produced by the same curvature fluctuations. I will demonstrate that the resulting GW signals will be well within the sensitivity of future detectors such as LISA, DECIGO, BBO, and the Einstein Telescope. The multimessenger signal from the observed gamma-rays and GWs will allow a precise measurement of the primordial curvature perturbation that produces the PBH. I will also argue that the resulting correlation between the two types of observations can provide a smoking-gun signal of PBHs.

    3:30–4:00 pmAnson Hook
    (Virtual via Zoom)
    Title: Early Universe Cosmology from Stochastic Gravitational Waves

    Abstract:  The causal tail of stochastic gravitational waves can be used to probe the energy density in free streaming relativistic species as well as measure gstar and beta functions as a function of temperature. In the event of the discovery of loud stochastic gravitational waves, we demonstrate that LISA can measure the free streaming fraction of the universe down to the 10^-3 level, 100 times more sensitive than current constraints. Additionally, it would be sensitive to O(1) deviations of gstar and the QCD beta function from their Standard Model value at temperatures ~ 10^5 GeV. In this case, many motivated models such as split SUSY and other solutions to the Electroweak Hierarchy problem would be tested. Future detectors, such as DECIGO, would be 100 times more sensitive than LISA to these effects and be capable of testing other motivated scenarios such as WIMPs and axions. The amazing prospect of using precision gravitational wave measurements to test such well motivated theories provides a benchmark to aim for when developing a precise understanding of the gravitational wave spectrum both experimentally and theoretically.

     

    Wednesday, August 3, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amKai Schmitz
    (Virtual via Zoom)
    Title: Gravitational waves from metastable cosmic strings

    Abstract: Cosmic strings are predicted by many Standard Model extensions involving the cosmological breaking of an Abelian symmetry and represent a potential source of primordial gravitational waves (GWs). In many Grand Unified Theories (GUTs), cosmic strings especially turn out to be metastable, as the nucleation of GUT monopoles along strings after a finite lifetime eventually leads to the collapse of the entire string network. In this talk, I will discuss the theoretical description of such a network and its individual components as well as the consequences for the emitted GW spectrum. Remarkably, the GW signal from metastable strings may well explain the common-spectrum process recently observed in pulsar timing data, while at the same time and in contrast to stable cosmic strings predicting a signal at higher frequencies that is still within the reach of current-generation ground-based interferometers. On their way to design sensitivity, existing GW experiments will thus have a realistic chance to probe particle physics processes at energies close to the GUT scale via the observation of GWs from metastable strings. This talk is based on 2107.04578 in collaboration with Wilfried Buchmüller and Valerie Domcke.

    10:00–10:30 amOliver Gould
    (Virtual via Zoom)
    Title: Effective field theory for cosmological phase transitions

    Abstract: Phase transitions are driven by thermal loop fluctuations, which modify background fields at leading order. This breaks the loop expansion and leads to large theoretical uncertainties in typical calculations, especially for gravitational wave predictions. I will give an overview of our present understanding of these uncertainties, and of the tools that have been developed to overcome them. Effective field theory has been at the forefront of this development, and I will outline how it can be used to solve a number of decades-long-standing theoretical problems.

    10:30–11:00 amIsabel Garcia-GarciaTitle: The Rocket Science of Expanding Bubbles
    11:00–1:30 pmBreak
    1:30–3:00 pmLightning Talks 2Sarah Geller
    Peizhi Du
    Tong Ou
    Isaac Wang
    Katie Fraser
    3:00–3:30 pmDavid Dunsky
    (Virtual via Zoom)
    Title: Gravitational Wave Gastronomy

    Abstract: The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational wave fingerprints. In this talk, I will discuss the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and “eat” the strings, 2) the collapse and decay of a monopole-string network by strings that “eat” the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and “eat” the wall, and 4) the collapse and decay of a string-bounded wall network by walls that “eat” the strings. We call the gravitational wave signals produced from the “eating” of one topological defect by another “gravitational wave gastronomy”. The gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO(10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects.

    3:30–4:00 pmYanou Cui
    (Virtual via Zoom)
    Title: Cosmic Archaeology with gravitational waves from (axion) cosmic strings

    Abstract: In this talk I will discuss important aspects of cosmology and particle physics that can be probed with GW signals from cosmic strings: probing the pre-BBN primordial dark age and axion physics.  Gravitational waves (GWs) originating from the dynamics of a cosmic string network have the ability to probe many otherwise inaccessible properties of the early universe. In particular, I will discuss how the frequency spectrum of a stochastic GW background (SGWB) from a cosmic string network can be used to probe Hubble expansion rate of the early universe prior to Big Bang Nucleosynthesis (BBN), during the “primordial dark age”. Furthermore I will show that in contrast to the standard expectation, cosmic strings formed before inflation could regrow back into the horizon and leave imprints, with GW bursts potentially being the leading signal. In relation to axion physics I will also demonstrate the detection prospect for SGWB from global/axion strings which may provide a new probe for axion-like dark matter models, considering various scenarios of cosmic history.

    4:00–4:30 pmMichael NeeTitle: The Boring Monopole

    Abstract: First order phase transitions play an important role in the cosmology of many theories of BSM physics. In this talk I will discuss how a population of magnetic monopoles present in the early universe can seed first order phase transitions, causing them to proceed much more rapidly than in the usual case. The field profiles describing the decay do not have the typically assumed O(3)/O(4) symmetry, thus requiring an extension of the usual decay rate calculation. To numerically determine the saddle point solutions which describe the decay we use a new algorithm based on the mountain pass theorem. Our results show that monopole-catalysed tunnelling can dominate over the homogeneous decay for a wide range of parameters.

     

    Thursday, August 4, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amYikun WangTitle: A New Approach to Electroweak Symmetry Non-Restoration

    Abstract: Electroweak symmetry non-restoration up to high temperatures well above the electroweak scale has intriguing implications for (electroweak) baryogenesis and early universe thermal histories. In this talk, I will discuss such a possible fate of the electroweak symmetry in the early universe and a new approach to realize it, via an inert Higgs sector that couples to the Standard Model Higgs as well as an extended scalar singlet sector. Examples of benchmark scenarios that allow for electroweak symmetry non-restoration all the way up to hundreds of TeV temperatures, at the same time featuring suppressed sphaleron washout factors down to the electroweak scale, will be presented. Renormalization group improvements and thermal resummation, necessary to evaluate the effective potential spanning over a broad range of energy scales and temperatures, have been implemented calculating the thermal history. This method for transmitting the Standard Model broken electroweak symmetry to an inert Higgs sector can be scrutinized through Higgs physics phenomenology and electroweak precision measurements at the HL-LHC.

    10:00–10:30 amSoubhik KumarTitle: Probing primordial fluctuations through stochastic gravitational wave background anisotropies

    Abstract: Stochastic gravitational wave backgrounds are expected to be anisotropic. While such anisotropies can be of astrophysical origin, a cosmological component of such anisotropies can carry rich information about primordial perturbations. Focusing on the case of a cosmological phase transition, I will talk about how such anisotropies can give us a powerful probe of primordial non-Gaussianities, complementary to current and future CMB and LSS searches. In the scenario where astrophysical foregrounds are also present, I will then discuss some strategies using which we can extract the cosmological signal, focusing on the case of LISA, Taiji and BBO, in particular.

    10:30–11:00 amJessica Howard
    (Virtual via Zoom)
    Title: Dark Matter Freeze-out during SU(2)_L Confinement

    Abstract: We explore the possibility that dark matter is a pair of SU(2)_L doublets and propose a novel mechanism of dark matter production that proceeds through the confinement of the weak sector of the Standard Model. This phase of confinement causes the Standard Model doublets and dark matter to confine into pion-like objects. Before the weak sector deconfines, the dark pions freezeout and generate a relic abundance of dark matter. We solve the Boltzmann equations for this scenario to determine the scale of confinement and constituent dark matter mass required to produce the observed relic density. We determine which regions of this parameter space evade direct detection and collider bounds.

    11:00–11:30 amJuven WangTitle: Quantum Matter Adventure to Beyond the Standard Model Prediction

    Abstract: Ideas developed from the quantum matter and quantum field theory frontier may guide us to explore new physics beyond the 4d Standard Model. I propose a few such ideas. First, new physics for neutrinos: right-handed neutrinos carry a Z_{16} class mixed gauge-gravitational global anomaly index, which could be replaced by 4d or 5d topological quantum field theory, or 4d interacting conformal field theory. These theories provide possible new neutrino mass mechanisms [arXiv:2012.15860]. Second, deconfined quantum criticality between Grand Unified Theories: dictated by a Z_2 class global anomaly, a gapless quantum critical region can happen between Georgi-Glashow and Pati-Salam models as deformation of the Standard Model, where Beyond the Standard Model physics and Dark Gauge sector occur as neighbor phases [arXiv:2106.16248, arXiv:2112.14765, arXiv:2204.08393]. Third, the Strong CP problem can be solved by a new solution involving Symmetric Mass Generation [arXiv:2204.14271].

    11:30–1:30 pmBreak
    1:30–4:00 pmStephen R. TaylorTitle: Pulsar Timing Arrays: The Next Window onto the Low-frequency Gravitational-wave Universe

    Abstract: The nanohertz-frequency band of gravitational waves should be awash with signals from supermassive black-hole binaries, as well as cosmological signatures of phase transitions, cosmic strings, and other relics of the early Universe. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav) and the International Pulsar Timing Array are poised to chart this new frontier of gravitational wave discovery within the next several years. I will present exciting new results from recent cutting-edge searches, discuss some milestones on the road to the next decade of PTA discovery, and take workshop attendees through a guided tutorial of how the broader community can use our production-level analysis pipeline to extract new science with ease.

     

    Friday, August 5, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amOfri TelemTitle: Charge-Monopole Pairwise Phases from Dressed Quantum States
    10:00–10:30 amSungwoo HongTitle: Coupling a Cosmic String to a TQFT

    Abstract: In the last few years, the notion of symmetry has been enlarged to “generalized symmetry” or “higher-form symmetry” and these more generalized symmetries have played a critical role in deepening our understanding of QFT, notably IR phases of QFT. In this talk, I will discuss a various ways of coupling the axion-Maxwell theory to a topological field theory (TQFT). Contrary to a common wisdom, I will show that such topological modifications can lead to direct changes in the local physics with possible observable consequences. This surprise can be realized by a dimensional reduction, namely, a coupling to a TQFT in 4d leads to a non-trivial and local impact on the 2d string world-sheet QFT. There also exists a topological modification of the theory, i.e. gauging a discrete subgroup of 0-form shift symmetry, and this time it results in a alteration of spectrum of cosmic strings. If time permits, I will also discuss generalized symmetries and associated higher-groups of these theories.

    10:30–11:00 amEleanor Hall
    (Virtual via Zoom)
    Title: Non-perturbative methods for false vacuum decay

    Abstract: Gravitational waves from phase transitions in the early universe are one of our most promising signal channels of BSM physics; however, existing methods for predicting these signals are limited to weakly-coupled theories. In this talk, I present the quasi-stationary effective action, a new non-perturbative formalism for false vacuum decay that integrates over local fluctuations in field space using the functional renormalization group. This method opens the door to reliable calculation of gravitational wave signals and false vacuum decay rates for strongly-interacting theories. I will also discuss recent developments and ongoing extensions of the QSEA.

    11:00–1:30 pmBreak
    1:30–2:00 pmMrunal KorwarTitle: Electroweak Symmetric Balls

    Abstract: Electroweak symmetric balls are macroscopic objects with electroweak symmetry restored inside. Such an object can arise in models where dark sectors contain monopole or non-topological soliton with a Higgs portal interaction to the Standard Model. It could be produced in the early universe via phase transition or parametric resonance, accounting for all dark matter. In a scenario where the balls are allowed to evaporate, the observed baryon asymmetry in our universe could be explained by a mechanism of “catalyzed baryogenesis.” In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions via electroweak Sphaleron. Because of electroweak symmetric cores, such objects have a large geometric cross-section off a nucleus, generating a multi-hit signature in large volume detectors. These objects could radiatively capture a nucleus and release GeV-scale energy for each interaction. The IceCube detector can probe dark matter balls with masses up to a gram.

    2:00–2:30 pmSeth KorenTitle: Discrete Gauged Baryon Minus Lepton Number and the Cosmological Lithium Problem

    Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.
    The cosmological lithium problem—that theory predicts a primordial abundance thrice as high as that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

    2:30–3:00 pmYann GouttenoireTitle: Supercool Composite Dark Matter beyond 100 TeV

     

    Phase-Transitions_Poster

5
  • Phase Transitions and Topological Defects in the Early Universe
    09:00 -17:00
    2022-08-05-2022-08-05
    CMSA, 20 Garden Street, Cambridge, MA 02138 USA
    Phase-Transitions_banner-1536x407-1

    On August 2–5, the CMSA hosted a workshop on Phase Transitions and Topological Defects in the Early Universe.

    The workshop was held in room G10 of the CMSA, located at 20 Garden Street, Cambridge, MA and online via Zoom webinar.

    The next decade will see a wealth of new cosmological data, which can lead to new insights into fundamental physics. Upcoming facilities (such as LISA) will be able to probe signals of fascinating phenomena in the early universe. These include signals from “Phase Transitions and Topological Defects,” which are ubiquitously given rise to in well-motivated UV models. In-depth studies of such signals requires cross-talks between experts from a wide spectrum of fields.

    The workshop aims to provide a platform for efficient exchange of new ideas related to these topics. It will start with an overview of some of the past and future experimental efforts. Next, there will be a substantial number of talks probing different aspects of phenomenology of phase transitions and topological defects in the early universe. It will finally close with discussions on recent formal development in the field.

    Scientific Advisory: Julian B. Muñoz, Lisa Randall, Matthew Reece, Tracy Slatyer, Shing-Tung Yau

    Organizers:
    Harvard: Nick DePorzio, Katie Fraser, Sam Homiller, Rashmish Mishra, & Aditya Parikh
    MIT: Pouya Asadi, Marianne Moore, & Yitian Sun

    Schedule/Format
    There will be 20+ 10 minute talks, ample discussion time, and lightning chalkboard talks.

    Speakers:

    • Nancy Aggarwal (Northwestern)
    • Jae Hyeok Chang (UMD – JHU)
    • Yanou Cui (UC Riverside)
    • David Dunsky (UC Berkeley)
    • Isabel Garcia-Garcia (KITP – UCSB)
    • Oliver Gould (Nottingham)
    • Yann Gouttenoire (Tel Aviv)
    • Eleanor Hall (UC Berkeley)
    • Sungwoo Hong (Chicago)
    • Anson Hook (UMD)
    • Jessica Howard (UC Irvine)
    • Seth Koren (Chicago)
    • Mrunal Korwar (Wisconsin)
    • Soubhik Kumar (UC Berkeley)
    • Vuk Mandic (Minnesota)
    • Yuto Minami (Osaka)
    • Michael Nee (Oxford)
    • Kai Schmitz (CERN)
    • Stephen R. Taylor (Vanderbilt)
    • Ofri Telem (UC Berkeley)
    • Juven Wang (Harvard)
    • Yikun Wang (Caltech)

    Participants:

    • Manuel Buen Abad (UMD)
    • Pouya Asadi (MIT)
    • Sean Benevedes (MIT)
    • Sandipan Bhattacherjee (Birla Institute of Technology Mesra Ranchi India)
    • Xingang Chen (Harvard University)
    • Nicholas DePorzio (Harvard University)
    • Peizhi Du (Stony Brook University)
    • Nicolas Fernandez (University of Illinois Urbana-Champaign)
    • Joshua Foster (MIT)
    • Katherine Fraser (Harvard University)
    • Sarah Geller (MIT)
    • Aurora Ireland (University of Chicago)
    • Marius Kongsore (New York University)
    • Ho Tat Lam (Massachusetts Institute of Technology)
    • Lingfeng Li (Brown University)
    • Yingying Li (Fermilab)
    • Gustavo Marques-Tavares (UMD)
    • Rashmish Mishra (Harvard University)
    • Siddharth Mishra-Sharma (MIT/Harvard University)
    • Toby Opferkuch (UC Berkeley)
    • Tong Ou (University of Chicago)
    • Aditya Parikh (Harvard University)
    • Yitian Sun (MIT)
    • Juan Sebastian Valbuena-Bermudez (Ludwig Maximilian University of Munich and Max Planck Institute for Physics)
    • Isaac Wang (Rutgers)
    • Wei Xue (University of Florida)
    • Winston Yin (UC Berkeley)
    • Quratulain Zahoor (The Islamia University of Bahwalpur Punjab (Pakistan)

    Schedule

    Tuesday, August 2, 2022

    9:00–9:20 amBreakfast
    9:20–9:30 amRashmish MishraOpening Remarks
    9:30–10:00 amVuk MandicTitle: Searching for the Stochastic Gravitational Wave Background with LISA

    Abstract: The upcoming space-borne gravitational wave detector Laser Interferometer Space Antenna (LISA) will open a window into the milliHertz band of the gravitational wave spectrum. Among the many sources in this band is the stochastic gravitational wave background (SGWB), arising as an incoherent superposition of many uncorrelated gravitational wave sources. The SGWB could be of cosmological origin, carrying unique information about the physical processes that took place within the first minute after the big bang, including possible phase transitions and topological defects. LISA therefore has the potential to illuminate particle physics at very high energy scales that may be inaccessible in laboratories. I will discuss how LISA can be used to search for the SGWB, highlighting a new pipeline developed for this purpose as well as several challenges and limitations that such a search will encounter.

    10:00–10:30 amNancy AggarwalTitle: Gravitational waves at frequencies above 10 kHz

    Abstract: Gravitational waves (GWs) at frequencies higher than the LIGO band can bring us completely new information about the universe. Besides being the most-interesting frequency region for looking at cosmological phenomena, they can also convey signatures of ultralight bosons through blackhole superradiance and light primordial blackholes (PBHs). I will introduce a new global initiative to study GW sources and detectors at ultra-high-frequencies (MHz-GHz), as well as a new experiment at Northwestern University to look for GWs in the frequency band of 10 kHz to 300 kHz using levitated optomechanical sensors. I will summarize the design, the current experimental progress, as well as a path forward for future improvements.

    10:30–11:00 amYuto MinamiTitle: New measurements of the cosmic birefringence

    Abstract: Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation I report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite released in 2018. The statistical significance of the measured signal is 2.4 sigma. Recently, we found a signal with 3.3 sigma statistical significance when we use the latest Planck data and consider an effect of polarised foreground emission. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

    11:00–1:30 pmBreak
    1:30–3:00 pmLighting Talks 1Lingfeng Li
    Winston Yin
    Marius Kongsore
    Nick DePorzio
    3:00–3:30 pmJae Hyeok ChangTitle: Correlating gravitational wave and gamma-ray signals from primordial black holes

    Abstract: Asteroid-mass primordial black holes (PBHs) can explain the observed dark matter abundance while being consistent with the current indirect detection constraints. These PBHs can produce gamma-ray signals from Hawking radiation that are within the sensitivity of future measurements by the AMEGO and e-ASTROGAM experiments. PBHs which give rise to such observable gamma-ray signals have a cosmic origin from large primordial curvature fluctuations. There must then be a companion, stochastic gravitational wave (GW) background produced by the same curvature fluctuations. I will demonstrate that the resulting GW signals will be well within the sensitivity of future detectors such as LISA, DECIGO, BBO, and the Einstein Telescope. The multimessenger signal from the observed gamma-rays and GWs will allow a precise measurement of the primordial curvature perturbation that produces the PBH. I will also argue that the resulting correlation between the two types of observations can provide a smoking-gun signal of PBHs.

    3:30–4:00 pmAnson Hook
    (Virtual via Zoom)
    Title: Early Universe Cosmology from Stochastic Gravitational Waves

    Abstract:  The causal tail of stochastic gravitational waves can be used to probe the energy density in free streaming relativistic species as well as measure gstar and beta functions as a function of temperature. In the event of the discovery of loud stochastic gravitational waves, we demonstrate that LISA can measure the free streaming fraction of the universe down to the 10^-3 level, 100 times more sensitive than current constraints. Additionally, it would be sensitive to O(1) deviations of gstar and the QCD beta function from their Standard Model value at temperatures ~ 10^5 GeV. In this case, many motivated models such as split SUSY and other solutions to the Electroweak Hierarchy problem would be tested. Future detectors, such as DECIGO, would be 100 times more sensitive than LISA to these effects and be capable of testing other motivated scenarios such as WIMPs and axions. The amazing prospect of using precision gravitational wave measurements to test such well motivated theories provides a benchmark to aim for when developing a precise understanding of the gravitational wave spectrum both experimentally and theoretically.

     

    Wednesday, August 3, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amKai Schmitz
    (Virtual via Zoom)
    Title: Gravitational waves from metastable cosmic strings

    Abstract: Cosmic strings are predicted by many Standard Model extensions involving the cosmological breaking of an Abelian symmetry and represent a potential source of primordial gravitational waves (GWs). In many Grand Unified Theories (GUTs), cosmic strings especially turn out to be metastable, as the nucleation of GUT monopoles along strings after a finite lifetime eventually leads to the collapse of the entire string network. In this talk, I will discuss the theoretical description of such a network and its individual components as well as the consequences for the emitted GW spectrum. Remarkably, the GW signal from metastable strings may well explain the common-spectrum process recently observed in pulsar timing data, while at the same time and in contrast to stable cosmic strings predicting a signal at higher frequencies that is still within the reach of current-generation ground-based interferometers. On their way to design sensitivity, existing GW experiments will thus have a realistic chance to probe particle physics processes at energies close to the GUT scale via the observation of GWs from metastable strings. This talk is based on 2107.04578 in collaboration with Wilfried Buchmüller and Valerie Domcke.

    10:00–10:30 amOliver Gould
    (Virtual via Zoom)
    Title: Effective field theory for cosmological phase transitions

    Abstract: Phase transitions are driven by thermal loop fluctuations, which modify background fields at leading order. This breaks the loop expansion and leads to large theoretical uncertainties in typical calculations, especially for gravitational wave predictions. I will give an overview of our present understanding of these uncertainties, and of the tools that have been developed to overcome them. Effective field theory has been at the forefront of this development, and I will outline how it can be used to solve a number of decades-long-standing theoretical problems.

    10:30–11:00 amIsabel Garcia-GarciaTitle: The Rocket Science of Expanding Bubbles
    11:00–1:30 pmBreak
    1:30–3:00 pmLightning Talks 2Sarah Geller
    Peizhi Du
    Tong Ou
    Isaac Wang
    Katie Fraser
    3:00–3:30 pmDavid Dunsky
    (Virtual via Zoom)
    Title: Gravitational Wave Gastronomy

    Abstract: The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational wave fingerprints. In this talk, I will discuss the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and “eat” the strings, 2) the collapse and decay of a monopole-string network by strings that “eat” the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and “eat” the wall, and 4) the collapse and decay of a string-bounded wall network by walls that “eat” the strings. We call the gravitational wave signals produced from the “eating” of one topological defect by another “gravitational wave gastronomy”. The gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO(10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects.

    3:30–4:00 pmYanou Cui
    (Virtual via Zoom)
    Title: Cosmic Archaeology with gravitational waves from (axion) cosmic strings

    Abstract: In this talk I will discuss important aspects of cosmology and particle physics that can be probed with GW signals from cosmic strings: probing the pre-BBN primordial dark age and axion physics.  Gravitational waves (GWs) originating from the dynamics of a cosmic string network have the ability to probe many otherwise inaccessible properties of the early universe. In particular, I will discuss how the frequency spectrum of a stochastic GW background (SGWB) from a cosmic string network can be used to probe Hubble expansion rate of the early universe prior to Big Bang Nucleosynthesis (BBN), during the “primordial dark age”. Furthermore I will show that in contrast to the standard expectation, cosmic strings formed before inflation could regrow back into the horizon and leave imprints, with GW bursts potentially being the leading signal. In relation to axion physics I will also demonstrate the detection prospect for SGWB from global/axion strings which may provide a new probe for axion-like dark matter models, considering various scenarios of cosmic history.

    4:00–4:30 pmMichael NeeTitle: The Boring Monopole

    Abstract: First order phase transitions play an important role in the cosmology of many theories of BSM physics. In this talk I will discuss how a population of magnetic monopoles present in the early universe can seed first order phase transitions, causing them to proceed much more rapidly than in the usual case. The field profiles describing the decay do not have the typically assumed O(3)/O(4) symmetry, thus requiring an extension of the usual decay rate calculation. To numerically determine the saddle point solutions which describe the decay we use a new algorithm based on the mountain pass theorem. Our results show that monopole-catalysed tunnelling can dominate over the homogeneous decay for a wide range of parameters.

     

    Thursday, August 4, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amYikun WangTitle: A New Approach to Electroweak Symmetry Non-Restoration

    Abstract: Electroweak symmetry non-restoration up to high temperatures well above the electroweak scale has intriguing implications for (electroweak) baryogenesis and early universe thermal histories. In this talk, I will discuss such a possible fate of the electroweak symmetry in the early universe and a new approach to realize it, via an inert Higgs sector that couples to the Standard Model Higgs as well as an extended scalar singlet sector. Examples of benchmark scenarios that allow for electroweak symmetry non-restoration all the way up to hundreds of TeV temperatures, at the same time featuring suppressed sphaleron washout factors down to the electroweak scale, will be presented. Renormalization group improvements and thermal resummation, necessary to evaluate the effective potential spanning over a broad range of energy scales and temperatures, have been implemented calculating the thermal history. This method for transmitting the Standard Model broken electroweak symmetry to an inert Higgs sector can be scrutinized through Higgs physics phenomenology and electroweak precision measurements at the HL-LHC.

    10:00–10:30 amSoubhik KumarTitle: Probing primordial fluctuations through stochastic gravitational wave background anisotropies

    Abstract: Stochastic gravitational wave backgrounds are expected to be anisotropic. While such anisotropies can be of astrophysical origin, a cosmological component of such anisotropies can carry rich information about primordial perturbations. Focusing on the case of a cosmological phase transition, I will talk about how such anisotropies can give us a powerful probe of primordial non-Gaussianities, complementary to current and future CMB and LSS searches. In the scenario where astrophysical foregrounds are also present, I will then discuss some strategies using which we can extract the cosmological signal, focusing on the case of LISA, Taiji and BBO, in particular.

    10:30–11:00 amJessica Howard
    (Virtual via Zoom)
    Title: Dark Matter Freeze-out during SU(2)_L Confinement

    Abstract: We explore the possibility that dark matter is a pair of SU(2)_L doublets and propose a novel mechanism of dark matter production that proceeds through the confinement of the weak sector of the Standard Model. This phase of confinement causes the Standard Model doublets and dark matter to confine into pion-like objects. Before the weak sector deconfines, the dark pions freezeout and generate a relic abundance of dark matter. We solve the Boltzmann equations for this scenario to determine the scale of confinement and constituent dark matter mass required to produce the observed relic density. We determine which regions of this parameter space evade direct detection and collider bounds.

    11:00–11:30 amJuven WangTitle: Quantum Matter Adventure to Beyond the Standard Model Prediction

    Abstract: Ideas developed from the quantum matter and quantum field theory frontier may guide us to explore new physics beyond the 4d Standard Model. I propose a few such ideas. First, new physics for neutrinos: right-handed neutrinos carry a Z_{16} class mixed gauge-gravitational global anomaly index, which could be replaced by 4d or 5d topological quantum field theory, or 4d interacting conformal field theory. These theories provide possible new neutrino mass mechanisms [arXiv:2012.15860]. Second, deconfined quantum criticality between Grand Unified Theories: dictated by a Z_2 class global anomaly, a gapless quantum critical region can happen between Georgi-Glashow and Pati-Salam models as deformation of the Standard Model, where Beyond the Standard Model physics and Dark Gauge sector occur as neighbor phases [arXiv:2106.16248, arXiv:2112.14765, arXiv:2204.08393]. Third, the Strong CP problem can be solved by a new solution involving Symmetric Mass Generation [arXiv:2204.14271].

    11:30–1:30 pmBreak
    1:30–4:00 pmStephen R. TaylorTitle: Pulsar Timing Arrays: The Next Window onto the Low-frequency Gravitational-wave Universe

    Abstract: The nanohertz-frequency band of gravitational waves should be awash with signals from supermassive black-hole binaries, as well as cosmological signatures of phase transitions, cosmic strings, and other relics of the early Universe. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav) and the International Pulsar Timing Array are poised to chart this new frontier of gravitational wave discovery within the next several years. I will present exciting new results from recent cutting-edge searches, discuss some milestones on the road to the next decade of PTA discovery, and take workshop attendees through a guided tutorial of how the broader community can use our production-level analysis pipeline to extract new science with ease.

     

    Friday, August 5, 2022

    9:00–9:30 amBreakfast
    9:30–10:00 amOfri TelemTitle: Charge-Monopole Pairwise Phases from Dressed Quantum States
    10:00–10:30 amSungwoo HongTitle: Coupling a Cosmic String to a TQFT

    Abstract: In the last few years, the notion of symmetry has been enlarged to “generalized symmetry” or “higher-form symmetry” and these more generalized symmetries have played a critical role in deepening our understanding of QFT, notably IR phases of QFT. In this talk, I will discuss a various ways of coupling the axion-Maxwell theory to a topological field theory (TQFT). Contrary to a common wisdom, I will show that such topological modifications can lead to direct changes in the local physics with possible observable consequences. This surprise can be realized by a dimensional reduction, namely, a coupling to a TQFT in 4d leads to a non-trivial and local impact on the 2d string world-sheet QFT. There also exists a topological modification of the theory, i.e. gauging a discrete subgroup of 0-form shift symmetry, and this time it results in a alteration of spectrum of cosmic strings. If time permits, I will also discuss generalized symmetries and associated higher-groups of these theories.

    10:30–11:00 amEleanor Hall
    (Virtual via Zoom)
    Title: Non-perturbative methods for false vacuum decay

    Abstract: Gravitational waves from phase transitions in the early universe are one of our most promising signal channels of BSM physics; however, existing methods for predicting these signals are limited to weakly-coupled theories. In this talk, I present the quasi-stationary effective action, a new non-perturbative formalism for false vacuum decay that integrates over local fluctuations in field space using the functional renormalization group. This method opens the door to reliable calculation of gravitational wave signals and false vacuum decay rates for strongly-interacting theories. I will also discuss recent developments and ongoing extensions of the QSEA.

    11:00–1:30 pmBreak
    1:30–2:00 pmMrunal KorwarTitle: Electroweak Symmetric Balls

    Abstract: Electroweak symmetric balls are macroscopic objects with electroweak symmetry restored inside. Such an object can arise in models where dark sectors contain monopole or non-topological soliton with a Higgs portal interaction to the Standard Model. It could be produced in the early universe via phase transition or parametric resonance, accounting for all dark matter. In a scenario where the balls are allowed to evaporate, the observed baryon asymmetry in our universe could be explained by a mechanism of “catalyzed baryogenesis.” In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions via electroweak Sphaleron. Because of electroweak symmetric cores, such objects have a large geometric cross-section off a nucleus, generating a multi-hit signature in large volume detectors. These objects could radiatively capture a nucleus and release GeV-scale energy for each interaction. The IceCube detector can probe dark matter balls with masses up to a gram.

    2:00–2:30 pmSeth KorenTitle: Discrete Gauged Baryon Minus Lepton Number and the Cosmological Lithium Problem

    Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.
    The cosmological lithium problem—that theory predicts a primordial abundance thrice as high as that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

    2:30–3:00 pmYann GouttenoireTitle: Supercool Composite Dark Matter beyond 100 TeV

     

    Phase-Transitions_Poster

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  • Big Data Conference 2022
    09:00 -13:00
    2022-08-26
    Big-Data-2022_cmsa-web

    On August 26, 2022 the CMSA hosted our eighth annual Conference on Big Data. The Big Data Conference features speakers from the Harvard community as well as scholars from across the globe, with talks focusing on computer science, statistics, math and physics, and economics.

    The 2022 Big Data Conference took place virtually on Zoom.

    Organizers:

    • Scott Duke Kominers, MBA Class of 1960 Associate Professor, Harvard Business
    • Horng-Tzer Yau, Professor of Mathematics, Harvard University
    • Sergiy Verstyuk, CMSA, Harvard University

    Speakers:

    Schedule

    9:00 amConference OrganizersIntroduction and Welcome
    9:10 am – 9:55 amXiaohong ChenTitle: On ANN optimal estimation and inference for policy functionals of nonparametric conditional moment restrictions

    Abstract:  Many causal/policy parameters of interest are expectation functionals of unknown infinite-dimensional structural functions identified via conditional moment restrictions. Artificial Neural Networks (ANNs) can be viewed as nonlinear sieves that can approximate complex functions of high dimensional covariates more effectively than linear sieves. In this talk we present ANN optimal estimation and inference on  policy functionals, such as average elasticities or value functions, of unknown structural functions of endogenous covariates. We provide ANN efficient estimation and optimal t based confidence interval for regular policy functionals such as average derivatives in nonparametric instrumental variables regressions. We also present ANN quasi likelihood ratio based inference for possibly irregular policy functionals of general nonparametric conditional moment restrictions (such as quantile instrumental variables models or Bellman equations) for time series data. We conduct intensive Monte Carlo studies to investigate computational issues with ANN based optimal estimation and inference in economic structural models with endogeneity. For economic data sets that do not have very high signal to noise ratios, there are current gaps between theoretical advantage of ANN approximation theory vs inferential performance in finite samples.
    Some of the results are applied to efficient estimation and optimal inference for average price elasticity in consumer demand and BLP type demand.

    The talk is based on two co-authored papers:
    (1) Efficient Estimation of Average Derivatives in NPIV Models: Simulation Comparisons of Neural Network Estimators
    (Authors: Jiafeng Chen, Xiaohong Chen and Elie Tamer)
    https://arxiv.org/abs/2110.06763

    (2) Neural network Inference on Nonparametric conditional moment restrictions with weakly dependent data
    (Authors: Xiaohong Chen, Yuan Liao and Weichen Wang).

    View/Download Lecture Slides (pdf)

    10:00 am – 10:45 amJessica JeffersTitle: Labor Reactions to Credit Deterioration: Evidence from LinkedIn Activity

    Abstract: We analyze worker reactions to their firms’ credit deterioration. Using weekly networking activity on LinkedIn, we show workers initiate more connections immediately following a negative credit event, even at firms far from bankruptcy. Our results suggest that workers are driven by concerns about both unemployment and future prospects at their firm. Heightened networking activity is associated with contemporaneous and future departures, especially at financially healthy firms. Other negative events like missed earnings and equity downgrades do not trigger similar reactions. Overall, our results indicate that the build-up of connections triggered by credit deterioration represents a source of fragility for firms.

    10:50 am – 11:35 amMiles CranmerTitle: Interpretable Machine Learning for Physics

    Abstract: Would Kepler have discovered his laws if machine learning had been around in 1609? Or would he have been satisfied with the accuracy of some black box regression model, leaving Newton without the inspiration to discover the law of gravitation? In this talk I will explore the compatibility of industry-oriented machine learning algorithms with discovery in the natural sciences. I will describe recent approaches developed with collaborators for addressing this, based on a strategy of “translating” neural networks into symbolic models via evolutionary algorithms. I will discuss the inner workings of the open-source symbolic regression library PySR (github.com/MilesCranmer/PySR), which forms a central part of this interpretable learning toolkit. Finally, I will present examples of how these methods have been used in the past two years in scientific discovery, and outline some current efforts.

    View/Download Lecture Slides (pdf) 

    11:40 am – 12:25 pmDan RobertsTitle: A Statistical Model of Neural Scaling Laws

    Abstract: Large language models of a huge number of parameters and trained on near internet-sized number of tokens have been empirically shown to obey “neural scaling laws” for which their performance behaves predictably as a power law in either parameters or dataset size until bottlenecked by the other resource. To understand this better, we first identify the necessary properties allowing such scaling laws to arise and then propose a statistical model — a joint generative data model and random feature model — that captures this neural scaling phenomenology. By solving this model using tools from random matrix theory, we gain insight into (i) the statistical structure of datasets and tasks that lead to scaling laws (ii) how nonlinear feature maps, i.e the role played by the deep neural network, enable scaling laws when trained on these datasets, and (iii) how such scaling laws can break down, and what their behavior is when they do. A key feature is the manner in which the power laws that occur in the statistics of natural datasets are translated into power law scalings of the test loss, and how the finite extent of such power laws leads to both bottlenecks and breakdowns.

    View/Download Lecture Slides (pdf)

     

    12:30 pmConference OrganizersClosing Remarks

     

    Information about last year’s conference can be found here.

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