During 2022–23, the CMSA will host a seminar on Quantum Matter in Mathematics and Physics, organized by Juven Wang. This seminar will take place on Mondays at 9:30 am–11:00 am (Boston time). To learn how to attend this seminar, please fill out this form. The schedule will be updated as talks are confirmed.

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  • October 04, 2022 09:00 AM
Speaker: Justin Kulp
Title: Holomorphic Twists and Confinement in N= SYM
Venue: virtual

Quantum Matter Seminar Speaker: Justin Kulp (Perimeter Institute) Title: Holomorphic Twists and Confinement in N=1 SYM Abstract: Supersymmetric QFT’s are of long-standing interest for their high degree of solvability, phenomenological implications, and rich connections to mathematics. In my talk, I will describe how the holomorphic twist isolates the protected quantities which give SUSY QFTs their potency by restricting to the cohomology of one supercharge. I will briefly introduce infinite dimensional symmetry algebras, generalizing Virasoro and Kac-Moody symmetries, which emerge. Finally, I will explain a potential novel UV manifestation of confinement, dubbed “holomorphic confinement,” in the example of pure SU(N) super Yang-Mills. Based on arXiv:2207.14321 and 2 forthcoming works with Kasia Budzik, Davide Gaiotto, Brian Williams, Jingxiang Wu, and…

  • September 26, 2022 09:00 AM
Speaker: Avner Karasik
Title: Candidates for Non-Supersymmetric Dualities
Venue: virtual

Quantum Matter in Mathematics and Physics Speaker: Avner Karasik (University of Cambridge, UK) Title: Candidates for Non-Supersymmetric Dualities Abstract: In the talk I will discuss the possibility and the obstructions of finding non-supersymmetric dualities for 4d gauge theories. I will review consistency conditions based on Weingarten inequalities, anomalies and large N, and clarify some subtle points and misconceptions about them. Later I will go over some old and new examples of candidates for non-supersymmetric dualities. The will be based on 2208.07842  

  • September 13, 2022 09:30 AM
Speaker: Yichul Cho
Title: Non-invertible Symmetries in Nature
Venue: Virtual

Quantum Matter in Mathematics and Physics Speaker: Yichul Cho (SUNY Stony Brook) Title: Non-invertible Symmetries in Nature Abstract: In this talk, I will discuss non-invertible symmetries in familiar 3+1d quantum field theories describing our Nature. In massless QED, the classical U(1) axial symmetry is not completely broken by the ABJ anomaly. Instead, it turns into a discrete, non-invertible symmetry. The non-invertible symmetry operator is obtained by dressing the naïve U(1) axial symmetry operator with a fractional quantum Hall state. We also find a similar non-invertible symmetry in the massless limit of QCD, which provides an alternative explanation for the neutral pion decay. In the latter part of the talk, I will discuss non-invertible time-reversal symmetries in 3+1d gauge…

  • September 07, 2022 09:00 AM
Speaker: Zhengyan Darius Shi
Title: Gifts from anomalies: new results on quantum critical transport in non- Fermi liquids
Venue: CMSA Room G10

Quantum Matter in Mathematics and Physics Seminar Speaker: Zhengyan Darius Shi (MIT) Title: Gifts from anomalies: new results on quantum critical transport in non-Fermi liquids Abstract: Non-Fermi liquid phenomena arise naturally near Landau ordering transitions in metallic systems. Here, we leverage quantum anomalies as a powerful nonperturbative tool to calculate optical transport in these models in the infrared limit. While the simplest such models with a single boson flavor (N=1) have zero incoherent conductivity, a recently proposed large N deformation involving flavor-random Yukawa couplings between N flavors of bosons and fermions admits a nontrivial incoherent conductivity  (z is the boson dynamical exponent) when the order parameter is odd under inversion. The presence of incoherent conductivity in the random flavor model…

  • May 18, 2022 03:07 PM
Speaker: John McGreevy (UCSD)
Title: The Generalized Landau Paradigm (a review of generalized symmetries in condensed matter)
Venue: Virtual

Abstract: Recent advances in our understanding of symmetry in quantum many-body systems offer the possibility of a generalized Landau paradigm that encompasses all equilibrium phases of matter. This talk will be an elementary review of some of these developments, based on: https://arxiv.org/abs/2204.03045

  • May 12, 2022 03:05 PM
Speaker: Cari Cesarotti (Harvard)
Title: Oblique Lessons from the W Mass Measurement at CDF II
Venue: Virtual

Abstract: The CDF collaboration recently reported a new precise measurement of the W boson mass MW with a central value significantly larger than the SM prediction. We explore the effects of including this new measurement on a fit of the Standard Model (SM) to electroweak precision data. We characterize the tension of this new measurement with the SM and explore potential beyond the SM phenomena within the electroweak sector in terms of the oblique parameters S, T and U. We show that the large MW value can be accommodated in the fit by a large, nonzero value of U, which is difficult to construct in explicit models. Assuming U = 0, the electroweak fit strongly prefers large, positive values…

  • May 11, 2022 03:03 PM
Speaker: Brian Swingle (Brandeis)
Title: Cosmology from the vacuum
Venue: Virtual

Abstract: We are familiar with the idea that quantum gravity in AdS can holographically emerge from complex patterns of entanglement, but can the physics of big bang cosmology emerge from a quantum many-body system? In this talk I will argue that standard tools of holography can be used to describe fully non-perturbative microscopic models of cosmology in which a period of accelerated expansion may result from the positive potential energy of time-dependent scalar fields evolving towards a region with negative potential. In these models, the fundamental cosmological constant is negative, and the universe eventually recollapses in a time-reversal symmetric way. The microscopic description naturally selects a special state for the cosmology. In this framework, physics in the cosmological spacetime is dual to the vacuum physics in a static planar asymptotically AdS Lorentzian…

  • April 28, 2022 02:44 PM
Speaker: Shlomo S. Razamat (Technion)
Title: Aspects of d supersymmetric dynamics and geometry
Venue: Virtual

Abstract: We will overview the program of geometrically engineering four dimensional supersymmetric QFTs as compactifications of six dimensional SCFTs. In particular we will discuss how strong coupling phenomena in four dimensions, such as duality and emergence of symmetry, can be better understood in such geometric constructions.

  • April 22, 2022 02:43 PM
Speaker: Ruben Verresen (Harvard)
Title: Higgs = SPT
Venue: Virtual

Abstract: The Higgs phase of a gauge theory is important to both fundamental physics (e.g., electroweak theory) as well as condensed matter systems (superconductors and other emergent phenomena). However, such a charge condensate seems subtle and is sometimes described as the spontaneous breaking of gauge symmetry (or a global subgroup). In this talk, I will argue that the Higgs phase is best understood as a symmetry-protected topological (SPT) phase. The concept of SPT phases arose out of the condensed matter community, to describe systems with short-range entanglement and edge modes which cannot be removed in the presence of certain symmetries. The perspective that the Higgs phase is an SPT phase recovers known properties of the Higgs phase and provides…

  • April 14, 2022 02:39 PM
Speaker: Latham Boyle (Perimeter)
Title: Cancellation of the vacuum energy and Weyl anomaly in the standard model, and a two-sheeted, CPT-symmetric universe
Venue: Virtual

Abstract: I will explain a mechanism to cancel the vacuum energy and both terms in the Weyl anomaly in the standard model of particle physics, using conformally-coupled dimension-zero scalar fields.  Remarkably, given the standard model gauge group SU(3)xSU(2)xU(1), the cancellation requires precisely 48 Weyl spinors — i.e. three generations of standard model fermions, including right-handed neutrinos.  Moreover, the scalars possess a scale-invariant power spectrum, suggesting a new explanation for the observed primordial density perturbations in cosmology (without the need for inflation). As context, I will also introduce a related cosmological picture in which this cancellation mechanism plays an essential role.  Our universe seems to be dominated by radiation at early times, and positive vacuum energy at late times.  Taking…

  • April 13, 2022 02:37 PM
Speaker: Yoshio Kikukawa (U Tokyo)
Title: Why is the mission impossible? Decoupling the mirror Ginsparg-Wilson fermions in the lattice models for two-dimensional abelian chiral gauge theories
Venue: Virtual

Abstract: It has been known that the four-dimensional abelian chiral gauge theories of an anomaly-free set of Wely fermions can be formulated on the lattice preserving the exact gauge invariance and the required locality property in the framework of the Ginsparg- Wilson relation. This holds true in two dimensions. However, in the related formulation including the mirror Ginsparg-Wilson fermions, it has been argued that the mirror fermions do not decouple: in the 3450 model with Dirac- and Majorana-Yukawa couplings to XY-spin field, the two- point vertex function of the (external) gauge field in the mirror sector shows a singular non-local behavior in the so-called ParaMagnetic Strong-coupling(PMS) phase. We re-examine why the attempt seems a “Mission: Impossible” in the 3450…

  • April 07, 2022 02:35 PM
Speaker: Jung Hoon Han (Sungkyunkwan University, Suwon, South Korea)
Title: Lattice Gauge Theory View of Toric Codes, X-cube, and More
Venue: Virtual

Abstract: Exactly solvable spin models such as toric codes and X-cube model have heightened our understanding of spin liquids and topological matter in two and three dimensions. Their exact solvability, it turns out, is rooted in the existence of commuting generators in their parent lattice gauge theory (LGT). We can understand the toric codes as Higgsed descendants of the rank-1 U(1) LGT in two and three dimensions, and the X-cube model as that of rank-2 U(1) LGT in three dimensions. Furthermore, the transformation properties of the gauge fields in the respective LGT is responsible for, and nearly determines the structure of the effective field theory (EFT) of the accompanying matter fields. We show how to construct the EFT of…

  • April 06, 2022 02:27 PM
Speaker: Shaokai Jian (Brandeis)
Title: Late time von Neumann entropy and measurement-induced phase transition
Venue: Virtual

Abstract: Characterizing many-body entanglement is one of the most important problems in quantum physics. We present our studies on the steady state von Neumann entropy and its transition in Brownian SYK models. For unitary evolution, we show that the correlations between different replicas account for the Page curve at late time, and a permutation group structure emerges in the large-N calculation. In the presence of measurements, we find a transition of von Neumann entropy from volume-law to area-law by increasing the measurement rate. We show that a proper replica limit can be taken, which shows that the transition occurs at the point of replica symmetry breaking.

  • March 30, 2022 02:23 PM
Speaker: Jordan Cotler (Harvard)
Title: Renormalization group flow as optimal transport
Venue: Virtual

Abstract: We show that Polchinski’s equation for exact renormalization group flow is equivalent to the optimal transport gradient flow of a field-theoretic relative entropy.  This gives a surprising information-theoretic formulation of the exact renormalization group, expressed in the language of optimal transport.  We will provide reviews of both the exact renormalization group, as well as the theory of optimal transportation.  Our results allow us to establish a new, non-perturbative RG monotone, and also reformulate RG flow as a variational problem.  The latter enables new numerical techniques and allows us to establish a systematic connection between neural network methods and RG flows of conventional field theories.  Our techniques generalize to other RG flow equations beyond Polchinski’s.

  • March 24, 2022 02:17 PM
Speaker: Ruochen Ma (Perimeter Institute)
Title: Edge physics at the deconfined transition between a quantum spin Hall insulator and a superconductor
Venue: Virtual

Abstract: I will talk about the edge physics of the deconfined quantum phase transition (DQCP) between a spontaneous quantum spin Hall (QSH) insulator and a spin-singlet superconductor (SC). Although the bulk of this transition is in the same universality class as the paradigmatic deconfined Neel to valence-bond-solid transition, the boundary physics has a richer structure due to proximity to a quantum spin Hall state. We use the parton trick to write down an effective field theory for the QSH-SC transition in the presence of a boundary and calculate various edge properties in a large-N limit. We show that the boundary Luttinger liquid in the QSH state survives at the phase transition, but only as fractional degrees of freedom that…

  • March 23, 2022 02:14 PM
Speaker: Chong Wang (Perimeter Institute)
Title: Non-zero momentum requires long-range entanglement
Venue: Virtual

Abstract: I will show that a quantum state in a lattice spin (boson) system must be long-range entangled if it has non-zero lattice momentum, i.e. if it is an eigenstate of the translation symmetry with eigenvalue not equal to 1. Equivalently, any state that can be connected with a non-zero momentum state through a finite-depth local unitary transformation must also be long-range entangled. The statement can also be generalized to fermion systems. I will then present two applications of this result: (1) several different types of Lieb-Schultz-Mattis (LSM) theorems, including a previously unknown version involving only a discrete Z_n symmetry, can be derived in a simple manner; (2) a gapped topological order (in space dimension d>1) must weakly break…

  • March 17, 2022 02:11 PM
Speaker: Miguel Montero (Harvard University)
Title:  A Hike through the Swampland
Venue: Virtual

Abstract: The Swampland program aims at uncovering the universal implications of quantum gravity at low-energy physics. I will review the basic ideas of the Swampland program, formal and phenomenological implications, and provide a survey of the techniques commonly used in Swampland research including tools from quantum information, holography, supersymmetry, and string theory.

  • March 16, 2022 02:10 PM
Speaker: Gregory Moore (Rutgers)
Title: Summing Over Bordisms In d TQFT
Venue: Virtual

Abstract: Some recent work in the quantum gravity literature has considered what happens when the amplitudes of a TQFT are summed over the bordisms between fixed in-going and out-going boundaries. We will comment on these constructions. The total amplitude, that takes into account all in-going and out-going boundaries can be presented in a curious factorized form. This talk reports on work done with Anindya Banerjee and is based on the paper on the e-print arXiv  2201.00903.

  • March 10, 2022 02:08 PM
Speaker: Haoyu Guo (KITP & Harvard)
Title: Resonant side-jump thermal Hall effect of phonons coupled to dynamical defects
Venue: Virtual

Abstract: We present computations of the thermal Hall coefficient of phonons scattering off defects with multiple energy levels. Using a microscopic formulation based on the Kubo formula, we find that the leading contribution perturbative in the phonon-defect coupling is of the `side-jump’ type, which is proportional to the phonon lifetime. This contribution is at resonance when the phonon energy equals a defect level spacing. Our results are obtained for different defect models, and include models of an impurity quantum spin in the presence of quasi-static magnetic order with an isotropic Zeeman coupling to the applied field. This work is based on arxiv: 2201.11681

  • March 09, 2022 02:04 PM
Speaker: Simon Catterall (Syracuse University)
Title: Anomalies, topological insulators and Kaehler-Dirac fermions
Venue: Virtual

Abstract: Motivated by a puzzle arising from recent work on staggered lattice fermions we introduce Kaehler-Dirac fermions and describe their connection both to Dirac fermions and staggered fermions. We show that they suffer from a gravitational anomaly that breaks a chiral U(1) symmetry specific to Kaehler-Dirac fermions down to Z_4 in any even dimension. In odd dimensions we show that the effective theory that results from integrating out massive Kaehler-Dirac fermions is a topological gravity theory. Such theories generalize Witten’s construction of (2+1) gravity as a Chern Simons theory. In the presence of a domain wall massless modes appear on the wall which can be consistently coupled to gravity due to anomaly inflow from the bulk gravitational theory. Much of this story…