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DTSTART;TZID=America/New_York:20220730T090000
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DTSTAMP:20260406T120004
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SUMMARY:Advances in Mathematical Physics
DESCRIPTION:A Conference in Honor of Elliott H. Lieb on his 90th Birthday\nOn July 30 – Aug 1\, 2022 the Harvard Mathematics Department and the CMSA co-hosted a birthday conference in honor of Elliott Lieb. \nThis 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.). \nVenue:\nJuly 30–31\, 2022: Hall B\, Science Center\, 1 Oxford Street\, Cambridge\, MA\, 02138\nAugust 1\, 2022: Hall C\, Science Center\, 1 Oxford Street\, Cambridge\, MA\, 02138 \nSchedule (pdf) \nOrganizers:\nMichael Aizenman\, Princeton University\nJoel Lebowitz\, Rutgers University\nRuedi Seiler\, Technische Universität Berlin\nHerbert Spohn\, Technical University of Munich\nHorng-Tzer Yau\, Harvard University\nShing-Tung Yau\, Harvard University\nJakob Yngvason\, University of Vienna \nSPEAKERS:\nRafael Benguria\, Pontificia Universidad Catolica de Chile\nEric Carlen\, Rutgers University\nPhilippe Di Francesco\, University of Illinois\nHugo Duminil-Copin\, IHES\nLászló Erdös\, Institute of Science and Technology Austria\nRupert Frank\, Ludwig Maximilian University of Munich\nJürg Fröhlich\, ETH Zurich\nAlessandro Giuliani\, Università degli Studi Roma Tre\nBertrand Halperin\, Harvard University\nKlaus Hepp\, Institute for Theoretical Physics\, ETH Zurich\nSabine Jansen\, Ludwig Maximilian University of Munich\nMathieu Lewin\, Université Paris-Dauphine\nBruno Nachtergaele\, The University of California\, Davis\nYoshiko Ogata\, University of Tokyo\nRon Peled\, Tel Aviv University\nBenjamin Schlein\, University of Zurich\nRobert Seiringer\, Institute of Science and Technology Austria\nJan Philip Solovej\, University of Copenhagen\nHal Tasaki\, Gakushuin University\nSimone Warzel\, Technical University of Munich\nJun Yin\, The University of California\, Los Angeles \n 
URL:https://cmsa.fas.harvard.edu/event/advances-in-mathematical-physics/
LOCATION:Harvard Science Center\, 1 Oxford Street\, Cambridge\, MA\, 02138
CATEGORIES:Conference,Event
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/Elliott-Lieb-conference-2022_banner-2-1536x734-1.png
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DTSTART;TZID=America/New_York:20220802T090000
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SUMMARY:Phase Transitions and Topological Defects in the Early Universe
DESCRIPTION:On August 2–5\, the CMSA hosted a workshop on Phase Transitions and Topological Defects in the Early Universe. \nThe workshop was held in room G10 of the CMSA\, located at 20 Garden Street\, Cambridge\, MA and online via Zoom webinar. \nThe 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. \nThe 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. \nScientific Advisory: Julian B. Muñoz\, Lisa Randall\, Matthew Reece\, Tracy Slatyer\, Shing-Tung Yau \nOrganizers:\nHarvard: Nick DePorzio\, Katie Fraser\, Sam Homiller\, Rashmish Mishra\, & Aditya Parikh\nMIT: Pouya Asadi\, Marianne Moore\, & Yitian Sun \nSchedule/Format\nThere will be 20+ 10 minute talks\, ample discussion time\, and lightning chalkboard talks. \nSpeakers: \n\nNancy Aggarwal (Northwestern)\nJae Hyeok Chang (UMD – JHU)\nYanou Cui (UC Riverside)\nDavid Dunsky (UC Berkeley)\nIsabel Garcia-Garcia (KITP – UCSB)\nOliver Gould (Nottingham)\nYann Gouttenoire (Tel Aviv)\nEleanor Hall (UC Berkeley)\nSungwoo Hong (Chicago)\nAnson Hook (UMD)\nJessica Howard (UC Irvine)\nSeth Koren (Chicago)\nMrunal Korwar (Wisconsin)\nSoubhik Kumar (UC Berkeley)\nVuk Mandic (Minnesota)\nYuto Minami (Osaka)\nMichael Nee (Oxford)\nKai Schmitz (CERN)\nStephen R. Taylor (Vanderbilt)\nOfri Telem (UC Berkeley)\nJuven Wang (Harvard)\nYikun Wang (Caltech)\n\n\nParticipants: \n\nManuel Buen Abad (UMD)\nPouya Asadi (MIT)\nSean Benevedes (MIT)\nSandipan Bhattacherjee (Birla Institute of Technology Mesra Ranchi India)\nXingang Chen (Harvard University)\nNicholas DePorzio (Harvard University)\nPeizhi Du (Stony Brook University)\nNicolas Fernandez (University of Illinois Urbana-Champaign)\nJoshua Foster (MIT)\nKatherine Fraser (Harvard University)\nSarah Geller (MIT)\nAurora Ireland (University of Chicago)\nMarius Kongsore (New York University)\nHo Tat Lam (Massachusetts Institute of Technology)\nLingfeng Li (Brown University)\nYingying Li (Fermilab)\nGustavo Marques-Tavares (UMD)\nRashmish Mishra (Harvard University)\nSiddharth Mishra-Sharma (MIT/Harvard University)\nToby Opferkuch (UC Berkeley)\nTong Ou (University of Chicago)\nAditya Parikh (Harvard University)\nYitian Sun (MIT)\nJuan Sebastian Valbuena-Bermudez (Ludwig Maximilian University of Munich and Max Planck Institute for Physics)\nIsaac Wang (Rutgers)\nWei Xue (University of Florida)\nWinston Yin (UC Berkeley)\nQuratulain Zahoor (The Islamia University of Bahwalpur Punjab (Pakistan)\n\nSchedule \nTuesday\, August 2\, 2022 \n\n\n\n\n9:00–9:20 am\nBreakfast\n\n\n\n9:20–9:30 am\nRashmish Mishra\nOpening Remarks\n\n\n9:30–10:00 am\nVuk Mandic\nTitle: Searching for the Stochastic Gravitational Wave Background with LISA \nAbstract: 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. \n\n\n\n10:00–10:30 am\nNancy Aggarwal\nTitle: Gravitational waves at frequencies above 10 kHz \nAbstract: 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. \n\n\n\n10:30–11:00 am\nYuto Minami\nTitle: New measurements of the cosmic birefringence \nAbstract: 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. \n\n\n\n11:00–1:30 pm\nBreak\n\n\n\n1:30–3:00 pm\nLighting Talks 1\nLingfeng Li\nWinston Yin\nMarius Kongsore\nNick DePorzio\n\n\n3:00–3:30 pm\nJae Hyeok Chang\nTitle: Correlating gravitational wave and gamma-ray signals from primordial black holes \nAbstract: 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. \n\n\n\n3:30–4:00 pm\nAnson Hook\n(Virtual via Zoom)\nTitle: Early Universe Cosmology from Stochastic Gravitational Waves \nAbstract:  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. \n\n\n\n\n\n  \nWednesday\, August 3\, 2022 \n\n\n\n\n9:00–9:30 am\nBreakfast\n\n\n\n9:30–10:00 am\nKai Schmitz\n(Virtual via Zoom)\nTitle: Gravitational waves from metastable cosmic strings \nAbstract: 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. \n\n\n\n10:00–10:30 am\nOliver Gould\n(Virtual via Zoom)\nTitle: Effective field theory for cosmological phase transitions \nAbstract: 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. \n\n\n\n10:30–11:00 am\nIsabel Garcia-Garcia\nTitle: The Rocket Science of Expanding Bubbles \n\n\n\n11:00–1:30 pm\nBreak\n\n\n\n1:30–3:00 pm\nLightning Talks 2\nSarah Geller\nPeizhi Du\nTong Ou\nIsaac Wang\nKatie Fraser\n\n\n3:00–3:30 pm\nDavid Dunsky\n(Virtual via Zoom)\nTitle: Gravitational Wave Gastronomy \nAbstract: 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. \n\n\n\n3:30–4:00 pm\nYanou Cui\n(Virtual via Zoom)\nTitle: Cosmic Archaeology with gravitational waves from (axion) cosmic strings \nAbstract: 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. \n\n\n\n4:00–4:30 pm\nMichael Nee\nTitle: The Boring Monopole \nAbstract: 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. \n\n\n\n\n\n  \nThursday\, August 4\, 2022 \n\n\n\n\n9:00–9:30 am\nBreakfast\n\n\n\n9:30–10:00 am\nYikun Wang\nTitle: A New Approach to Electroweak Symmetry Non-Restoration \nAbstract: 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. \n\n\n\n10:00–10:30 am\nSoubhik Kumar\nTitle: Probing primordial fluctuations through stochastic gravitational wave background anisotropies \nAbstract: 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. \n\n\n\n10:30–11:00 am\nJessica Howard\n(Virtual via Zoom)\nTitle: Dark Matter Freeze-out during SU(2)_L Confinement \nAbstract: 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. \n\n\n\n11:00–11:30 am\nJuven Wang\nTitle: Quantum Matter Adventure to Beyond the Standard Model Prediction \nAbstract: 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]. \n\n\n\n11:30–1:30 pm\nBreak\n\n\n\n1:30–4:00 pm\nStephen R. Taylor\nTitle: Pulsar Timing Arrays: The Next Window onto the Low-frequency Gravitational-wave Universe \nAbstract: 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. \n\n\n\n\n\n  \nFriday\, August 5\, 2022 \n\n\n\n\n9:00–9:30 am\nBreakfast\n\n\n\n9:30–10:00 am\nOfri Telem\nTitle: Charge-Monopole Pairwise Phases from Dressed Quantum States \n\n\n\n10:00–10:30 am\nSungwoo Hong\nTitle: Coupling a Cosmic String to a TQFT \nAbstract: 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. \n\n\n\n10:30–11:00 am\nEleanor Hall\n(Virtual via Zoom)\nTitle: Non-perturbative methods for false vacuum decay \nAbstract: 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. \n\n\n\n11:00–1:30 pm\nBreak\n\n\n\n1:30–2:00 pm\nMrunal Korwar\nTitle: Electroweak Symmetric Balls \nAbstract: 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. \n\n\n\n2:00–2:30 pm\nSeth Koren\nTitle: Discrete Gauged Baryon Minus Lepton Number and the Cosmological Lithium Problem \nAbstract: 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.\nThe 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. \n\n\n\n2:30–3:00 pm\nYann Gouttenoire\nTitle: Supercool Composite Dark Matter beyond 100 TeV \n\n\n\n\n\n 
URL:https://cmsa.fas.harvard.edu/event/phase-transitions/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Event,Workshop
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/Phase-Transitions_Poster.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220810T090000
DTEND;TZID=America/New_York:20220810T100000
DTSTAMP:20260406T120005
CREATED:20240215T095253Z
LAST-MODIFIED:20240229T090234Z
UID:10002731-1660122000-1660125600@cmsa.fas.harvard.edu
SUMMARY:Recent Advances on Maximum Flows and Minimum-Cost Flows
DESCRIPTION:Interdisciplinary Science Seminar\n\n\n\n\n\n\nSpeaker: Yang P. Liu\n\n\nTitle: Recent Advances on Maximum Flows and Minimum-Cost Flows\n\nAbstract: We survey recent advances on computing flows in graphs\, culminating in an almost linear time algorithm for solving minimum-cost flow and several other problems to high accuracy on directed graphs. Along the way\, we will discuss intuitions from linear programming\, graph theory\, and data structures that influence these works\, and the resulting natural open problems. \nBio: Yang P. Liu is a final-year graduate student at Stanford University. He is broadly interested in the efficient design of algorithms\, particularly flows\, convex optimization\, and online algorithms. For his work\, he has been awarded STOC and ITCS best student papers.
URL:https://cmsa.fas.harvard.edu/event/iss_81022/
LOCATION:Virtual
CATEGORIES:Interdisciplinary Science Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220811T090000
DTEND;TZID=America/New_York:20220811T100000
DTSTAMP:20260406T120005
CREATED:20240215T095012Z
LAST-MODIFIED:20240229T085717Z
UID:10002730-1660208400-1660212000@cmsa.fas.harvard.edu
SUMMARY:Exploring and Exploiting the Universality Phenomena in High-Dimensional Estimation and Learning
DESCRIPTION:Interdisciplinary Science Seminar \nSpeaker: Yue M. Lu\, Harvard University \nTitle: Exploring and Exploiting the Universality Phenomena in High-Dimensional Estimation and Learning \nAbstract: Universality is a fascinating high-dimensional phenomenon. It points to the existence of universal laws that govern the macroscopic behavior of wide classes of large and complex systems\, despite their differences in microscopic details. The notion of universality originated in statistical mechanics\, especially in the study of phase transitions. Similar phenomena have been observed in probability theory\, dynamical systems\, random matrix theory\, and number theory.\nIn this talk\, I will present some recent progresses in rigorously understanding and exploiting the universality phenomena in the context of statistical estimation and learning on high-dimensional data. Examples include spectral methods for high-dimensional projection pursuit\, statistical learning based on kernel and random feature models\, and approximate message passing algorithms on highly structured\, strongly correlated\, and even (nearly) deterministic data matrices. Together\, they demonstrate the robustness and wide applicability of the universality phenomena. \nBio: Yue M. Lu attended the University of Illinois at Urbana-Champaign\, where he received the M.Sc. degree in mathematics and the Ph.D. degree in electrical engineering\, both in 2007.  He is currently Gordon McKay Professor of Electrical Engineering and of Applied Mathematics at Harvard University. He is also fortunate to have held visiting appointments at Duke University in 2016 and at the École Normale Supérieure (ENS) in 2019. His research interests include the mathematical foundations of statistical signal processing and machine learning in high dimensions.
URL:https://cmsa.fas.harvard.edu/event/iss_81122/
LOCATION:Hybrid
CATEGORIES:Interdisciplinary Science Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220816T100000
DTEND;TZID=America/New_York:20220816T113000
DTSTAMP:20260406T120005
CREATED:20240215T100758Z
LAST-MODIFIED:20240229T092227Z
UID:10002738-1660644000-1660649400@cmsa.fas.harvard.edu
SUMMARY:Transport in large-N critical Fermi surface
DESCRIPTION:Speaker: Haoyu Guo (Harvard) \nTitle: Transport in large-N critical Fermi surface\n\nAbstract: A Fermi surface coupled to a scalar field can be described in a 1/N expansion by choosing the fermion-scalar Yukawa coupling to be random in the N-dimensional flavor space\, but invariant under translations. We compute the conductivity of such a theory in two spatial dimensions for a critical scalar. We find a Drude contribution\, and show that a previously proposed \omega^{-2/3} contribution to the optical conductivity at frequency \omega has vanishing co-efficient. We also describe the influence of impurity scattering of the fermions\, and find that while the self energy resembles a marginal Fermi liquid\, the resistivity behaves like a Fermi liquid. Arxiv references: 2203.04990\, 2207.08841
URL:https://cmsa.fas.harvard.edu/event/qm_81622/
LOCATION:Virtual
CATEGORIES:Quantum Matter
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220818T100000
DTEND;TZID=America/New_York:20220818T103000
DTSTAMP:20260406T120005
CREATED:20240215T094804Z
LAST-MODIFIED:20240229T085424Z
UID:10002728-1660816800-1660818600@cmsa.fas.harvard.edu
SUMMARY:Scalable Dynamic Graph Algorithms
DESCRIPTION:CMSA Interdisciplinary Science Seminar \nSpeaker: Quanquan Liu\, Northwestern University \nTitle: Scalable Dynamic Graph Algorithms \nAbstract: The field of dynamic graph algorithms seeks to understand and compute statistics on real-world networks that undergo changes with time. Some of these networks could have up to millions of edge insertions and deletions per second. In light of these highly dynamic networks\, we propose various scalable and accurate graph algorithms for a variety of problems. In this talk\, I will discuss new algorithms for various graph problems in the batch-dynamic model in shared-memory architectures where updates to the graph arrive in multiple batches of one or more updates. I’ll also briefly discuss my work in other dynamic models such as distributed dynamic models where the communication topology of the network also changes with time (ITCS 2022). In these models\, I will present efficient algorithms for graph problems including k-core decomposition\, low out-degree orientation\, matching\, triangle counting\, and coloring. \nSpecifically\, in the batch-dynamic model where we are given a batch of B updates\, I’ll discuss an efficient O(B log^2 n) amortized work and O(log^2 n log log n) depth algorithm that gives a (2+\epsilon)-approximation on the k-core decomposition after each batch of updates (SPAA 2022). We also obtain new batch-dynamic algorithms for matching\, triangle counting\, and coloring using techniques and data structures developed in our k-core decomposition algorithm. In addition to our theoretical results\, we implemented and experimentally evaluated our k-core decomposition algorithm on a 30-core machine with two-way hyper-threading on 11 graphs of varying densities and sizes. Our experiments show improvements over state-of-the-art algorithms even on machines with only 4 cores (your standard laptop). I’ll conclude with a discussion of some open questions and potential future work that these lines of research inspire. \nBio: Quanquan C. Liu is a postdoctoral scholar at Northwestern University under the mentorship of Prof. Samir Khuller. She completed her PhD in Computer Science at MIT where she was advised by Prof. Erik Demaine and Prof. Julian Shun. Before that\, she obtained her dual bachelor’s degree in computer science and math also at MIT. She has worked on a number of problems in algorithms and the intersection between theory and practice. Her most recent work focuses on scalable dynamic and static graph algorithms as well as differentially private graph algorithms for problems including k-core decomposition\, densest subgraphs\, subgraph counting\, matching\, maximal independent set and coloring. She has earned the Best Paper Award at SPAA 2022\, a NSF Graduate Research Fellowship\, and participated in the 2021 EECS Rising Stars workshop. Outside of research\, she is extensively involved in programming outreach as a coach for the USA Computing Olympiad (USACO) and as a trainer for the North America Programming Camp (NAPC).
URL:https://cmsa.fas.harvard.edu/event/iss_81822/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Interdisciplinary Science Seminar
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220826T090000
DTEND;TZID=America/New_York:20220826T130000
DTSTAMP:20260406T120005
CREATED:20230705T044827Z
LAST-MODIFIED:20250328T145239Z
UID:10000058-1661504400-1661518800@cmsa.fas.harvard.edu
SUMMARY:Big Data Conference 2022
DESCRIPTION: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. \nThe 2022 Big Data Conference took place virtually on Zoom. \nOrganizers: \n\nScott Duke Kominers\, MBA Class of 1960 Associate Professor\, Harvard Business\nHorng-Tzer Yau\, Professor of Mathematics\, Harvard University\nSergiy Verstyuk\, CMSA\, Harvard University\n\nSpeakers: \n\nXiaohong Chen\, Yale\nMiles Cranmer\, Princeton\nJessica Jeffers\, University of Chicago\nDan Roberts\, MIT\n\nSchedule \n\n\n\n\n9:00 am\nConference Organizers\nIntroduction and Welcome\n\n\n9:10 am – 9:55 am\nXiaohong Chen\nTitle: On ANN optimal estimation and inference for policy functionals of nonparametric conditional moment restrictions \nAbstract:  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.\nSome of the results are applied to efficient estimation and optimal inference for average price elasticity in consumer demand and BLP type demand. \nThe talk is based on two co-authored papers:\n(1) Efficient Estimation of Average Derivatives in NPIV Models: Simulation Comparisons of Neural Network Estimators\n(Authors: Jiafeng Chen\, Xiaohong Chen and Elie Tamer)\nhttps://arxiv.org/abs/2110.06763 \n(2) Neural network Inference on Nonparametric conditional moment restrictions with weakly dependent data\n(Authors: Xiaohong Chen\, Yuan Liao and Weichen Wang). \nView/Download Lecture Slides (pdf)\n\n\n10:00 am – 10:45 am\nJessica Jeffers\nTitle: Labor Reactions to Credit Deterioration: Evidence from LinkedIn Activity \nAbstract: 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.\n\n\n10:50 am – 11:35 am\nMiles Cranmer\nTitle: Interpretable Machine Learning for Physics \nAbstract: 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. \nView/Download Lecture Slides (pdf) \n\n\n11:40 am – 12:25 pm\nDan Roberts\nTitle: A Statistical Model of Neural Scaling Laws \nAbstract: 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. \nView/Download Lecture Slides (pdf) \n \n\n\n12:30 pm\nConference Organizers\nClosing Remarks\n\n\n\n\n  \nInformation about last year’s conference can be found here.
URL:https://cmsa.fas.harvard.edu/event/big-data-conference-2022/
LOCATION:Virtual
CATEGORIES:Big Data Conference,Conference,Event
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/Big-Data-2022_web.png
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