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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211202T103000
DTEND;TZID=America/New_York:20211202T120000
DTSTAMP:20260514T162549
CREATED:20240213T070448Z
LAST-MODIFIED:20240213T070448Z
UID:10002156-1638441000-1638446400@cmsa.fas.harvard.edu
SUMMARY:12/2/21 Quantum Matter in Mathematics and Physics
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/12-2-21-quantum-matter-in-mathematics-and-physics/
LOCATION:MA
CATEGORIES:Quantum Matter
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211202T103000
DTEND;TZID=America/New_York:20211202T120000
DTSTAMP:20260514T162549
CREATED:20240301T083755Z
LAST-MODIFIED:20240301T083839Z
UID:10002887-1638441000-1638446400@cmsa.fas.harvard.edu
SUMMARY:Symmetry in quantum field theory and quantum gravity 2
DESCRIPTION:Speaker: Daniel Harlow (MIT) \nTitle: Symmetry in quantum field theory and quantum gravity 2 \nAbstract: In this talk I will give an overview of semi-recent work with Hirosi Ooguri arguing that three old conjectures about symmetry in quantum gravity are true in the AdS/CFT correspondence.  These conjectures are 1) that there are no global symmetries in quantum gravity\, 2) that dynamical objects transforming in all irreducible representations of any gauge symmetry must exist\, and 3) all internal gauge symmetries must be compact.  Along the way I will need to carefully define what we mean by gauge and global symmetries in quantum field theory and quantum gravity\, which leads to interesting applications in various related fields.  These definitions will be the focus of the first talk\, while the second will apply them to AdS/CFT to prove conjectures 1-3).
URL:https://cmsa.fas.harvard.edu/event/12-2-2021-quantum-matter-in-mathematics-and-physics/
LOCATION:MA
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-12.02.21-1544x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211202T130000
DTEND;TZID=America/New_York:20211202T140000
DTSTAMP:20260514T162549
CREATED:20240214T075408Z
LAST-MODIFIED:20240304T053731Z
UID:10002571-1638450000-1638453600@cmsa.fas.harvard.edu
SUMMARY:Kerr Geodesics and Self-consistent match between Inspiral and Transition-to-merger
DESCRIPTION:Abstract: The two-body motion in General Relativity can be solved perturbatively in the small mass ratio expansion. Kerr geodesics describe the leading order motion. After a short summary of the classification of polar and radial Kerr geodesic motion\, I will consider the inspiral motion of a point particle around the Kerr black hole subjected to the self-force. I will describe its quasi-circular inspiral motion in the radiation timescale expansion. I will describe in parallel the transition-to-merger motion around the last stable circular orbit and prove that it is controlled by the Painlevé transcendental equation of the first kind. I will then prove that one can consistently match the two motions using the method of asymptotically matched expansions.
URL:https://cmsa.fas.harvard.edu/event/12-2-2021-general-relativity-seminar/
LOCATION:MA
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211202T131500
DTEND;TZID=America/New_York:20211202T143000
DTSTAMP:20260514T162549
CREATED:20240213T113157Z
LAST-MODIFIED:20240304T084850Z
UID:10002504-1638450900-1638455400@cmsa.fas.harvard.edu
SUMMARY:Hydrodynamics and multi-scale order in confluent epithelia
DESCRIPTION:Abstract: In this talk I will review our ongoing theoretical and experimental efforts toward deciphering the hydrodynamic behavior of confluent epithelia. The ability of epithelial cells to collectively flow lies at the heart of a myriad of processes that are instrumental for life\, such as embryonic morphogenesis and wound healing\, but also of life-threatening conditions\, such as metastatic cancer. Understanding the physical origin of these mechanisms requires going beyond the current hydrodynamic theories of complex fluids and introducing a new theoretical framework\, able to account for biomechanical activity as well as for scale-dependent liquid crystalline order.
URL:https://cmsa.fas.harvard.edu/event/hydrodynamics-and-multi-scale-order-in-confluent-epithelia/
LOCATION:MA
CATEGORIES:Active Matter Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211202T142800
DTEND;TZID=America/New_York:20211202T152800
DTSTAMP:20260514T162549
CREATED:20240215T094151Z
LAST-MODIFIED:20240301T110349Z
UID:10002725-1638455280-1638458880@cmsa.fas.harvard.edu
SUMMARY:12/2/2021 Interdisciplinary Science Seminar
DESCRIPTION:Title: Polyhomogeneous expansions and Z/2-harmonic spinors branching along graphs \nAbstract: In this talk\, we will first reformulate the linearization of the moduli space of Z/2-harmonic spinorsv branching along a knot. This formula tells us that the kernel and cokernel of the linearization are isomorphic to the kernel and cokernel of the Dirac equation with a polyhomogeneous boundary condition. In the second part of this talk\, I will describe the polyhomogenous expansions for the Z/2-harmonic spinors branching along graphs and formulate the Dirac equation with a suitable boundary condition that can describe the perturbation of graphs with some restrictions. This is joint work with Andriy Haydys and Rafe Mazzeo.
URL:https://cmsa.fas.harvard.edu/event/12-2-2021-interdisciplinary-science-seminar/
LOCATION:MA
CATEGORIES:Interdisciplinary Science Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211203T093000
DTEND;TZID=America/New_York:20211203T103000
DTSTAMP:20260514T162549
CREATED:20240214T072504Z
LAST-MODIFIED:20240301T110847Z
UID:10002558-1638523800-1638527400@cmsa.fas.harvard.edu
SUMMARY:Black Holes\, 2D Gravity\, and Random Matrices
DESCRIPTION:Member Seminar \nSpeaker: Dan Kapec \nTitle: Black Holes\, 2D Gravity\, and Random Matrices \nAbstract: I will discuss old and new connections between black hole physics\, 2D quantum gravity\, and random matrix theory. Black holes are believed to be very complicated\, strongly interacting quantum mechanical systems\, and certain aspects of their Hamiltonians should be well approximated by random matrix theory. The near-horizon effective dynamics of near-extremal black holes is two-dimensional\, and many theories of 2D quantum gravity are known to have random matrix descriptions. All of these expectations were recently borne out in surprising detail with the solution of the Jackiw-Teitelboim (JT) model\, but this result raises more questions than it answers. If time permits\, I will discuss some extensions of these results and possible future directions.
URL:https://cmsa.fas.harvard.edu/event/12-3-2021-member-seminar/
LOCATION:MA
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211206T130000
DTEND;TZID=America/New_York:20211206T140000
DTSTAMP:20260514T162549
CREATED:20240214T112042Z
LAST-MODIFIED:20240301T074922Z
UID:10002695-1638795600-1638799200@cmsa.fas.harvard.edu
SUMMARY:Extremal Black Hole Corrections from Iyer-Wald
DESCRIPTION:Abstract: Extremal black holes play a key role in our understanding of various swampland conjectures and in particular the WGC. The mild form of the WGC states that higher-derivative corrections should decrease the mass of extremal black holes at fixed charge. Whether or not this conjecture is satisfied depends on the sign of the combination of Wilson coefficients that control corrections to extremality. Typically\, corrections to extremality need to be computed on a case-by-case basis\, but in this talk I will present a universal derivation of extremal black hole corrections using the Iyer-Wald formalism. This leads to a formula that expresses general corrections to the extremality bound in terms of the stress tensor of the perturbations under consideration\, clarifying the relation between the WGC and energy conditions. This shows that a necessary condition for the mild form of the WGC to be satisfied is a violation of the Dominant Energy Condition. This talk is based on 2111.04201.
URL:https://cmsa.fas.harvard.edu/event/12-6-2021-swampland-seminar/
LOCATION:MA
CATEGORIES:Swampland Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211207T093000
DTEND;TZID=America/New_York:20211207T103000
DTSTAMP:20260514T162549
CREATED:20230818T050741Z
LAST-MODIFIED:20240122T054102Z
UID:10001286-1638869400-1638873000@cmsa.fas.harvard.edu
SUMMARY:2d N=(0\,1) gauge theories\, Spin(7) orientifolds and triality
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/12-7-21-algebraic-geometry-in-string-theory/
LOCATION:Virtual
CATEGORIES:Algebraic Geometry in String Theory Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211207T093000
DTEND;TZID=America/New_York:20211207T103000
DTSTAMP:20260514T162549
CREATED:20240213T070713Z
LAST-MODIFIED:20240213T070713Z
UID:10002160-1638869400-1638873000@cmsa.fas.harvard.edu
SUMMARY:The singularity probability of random symmetric matrices
DESCRIPTION:Abstract: Let M_n be drawn uniformly from all n by n symmetric matrices with entries in {-1\,1}. In this talk I’ll consider the following basic question: what is the probability that M_n is singular? I’ll discuss recent joint work with Marcelo Campos\, Marcus Michelen and Julian Sahasrabudhe where we show that this probability is exponentially small. I hope to make the talk accessible to a fairly general audience.
URL:https://cmsa.fas.harvard.edu/event/the-singularity-probability-of-random-symmetric-matrices/
LOCATION:MA
CATEGORIES:Combinatorics Physics and Probability
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Combinatorics-Physics-and-Probability-Seminar-12.07.2021.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211208T093000
DTEND;TZID=America/New_York:20211208T103000
DTSTAMP:20260514T162549
CREATED:20240214T042604Z
LAST-MODIFIED:20240502T154649Z
UID:10002528-1638955800-1638959400@cmsa.fas.harvard.edu
SUMMARY:Induced subgraphs and tree decompositions
DESCRIPTION:Speaker: Maria Chudnovsky\, Princeton \nTitle: Induced subgraphs and tree decompositions \nAbstract: Tree decompositions are a powerful tool in both structural\ngraph theory and graph algorithms. Many hard problems become tractable if the input graph is known to have a tree decomposition of bounded “width”. Exhibiting a particular kind of a tree decomposition is also a useful way to describe the structure of a graph. \nTree decompositions have traditionally been used in the context of forbidden graph minors; bringing them into the realm of forbidden induced subgraphs has until recently remained out of reach. Over the last couple of years we have made significant progress in this direction\, exploring both the classical notion of bounded tree-width\, and concepts of more structural flavor. This talk will survey some of these ideas and results.
URL:https://cmsa.fas.harvard.edu/event/induced-subgraphs-and-tree-decompositions/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Colloquium-12.08.21-791x1024-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211208T103000
DTEND;TZID=America/New_York:20211208T120000
DTSTAMP:20260514T162549
CREATED:20240214T094451Z
LAST-MODIFIED:20240301T083428Z
UID:10002644-1638959400-1638964800@cmsa.fas.harvard.edu
SUMMARY:Defects\, link invariants and exact WKB
DESCRIPTION:Speaker: Fei Yan (Rutgers) \nTitle: Defects\, link invariants and exact WKB \nAbstract: I will describe some of my recent work on defects in supersymmetric field theories. The first part of my talk is focused on line defects in certain large classes of 4d N=2 theories and 3d N=2 theories. I will describe geometric methods to compute the ground states spectrum of the bulk-defect system\, as well as implications on the construction of link invariants. In the second part I will talk about some perspectives of surface defects in 4d N=2 theories and related applications on the exact WKB method for ordinary differential equations. This talk is based on past joint work with A. Neitzke\, various work in progress with D. Gaiotto\, S. Jeong\, A. Khan\, G. Moore\, as well as work by myself.
URL:https://cmsa.fas.harvard.edu/event/12-8-2021-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-12.08.21-1544x2048-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211208T140000
DTEND;TZID=America/New_York:20211208T150000
DTSTAMP:20260514T162549
CREATED:20230808T175752Z
LAST-MODIFIED:20240515T203917Z
UID:10001201-1638972000-1638975600@cmsa.fas.harvard.edu
SUMMARY:Hierarchical Transformers are More Efficient Language Models
DESCRIPTION:Speaker: Piotr Nawrot\, University of Warsaw \nTitle: Hierarchical Transformers are More Efficient Language Models \nAbstract: Transformer models yield impressive results on many NLP and sequence modeling tasks. Remarkably\, Transformers can handle long sequences which allows them to produce long coherent outputs: full paragraphs produced by GPT-3 or well-structured images produced by DALL-E. These large language models are impressive but also very inefficient and costly\, which limits their applications and accessibility. We postulate that having an explicit hierarchical architecture is the key to Transformers that efficiently handle long sequences. To verify this claim\, we first study different ways to upsample and downsample activations in Transformers so as to make them hierarchical. We use the best performing upsampling and downsampling layers to create Hourglass – a hierarchical Transformer language model. Hourglass improves upon the Transformer baseline given the same amount of computation and can yield the same results as Transformers more efficiently. In particular\, Hourglass sets new state-of-the-art for Transformer models on the ImageNet32 generation task and improves language modeling efficiency on the widely studied enwik8 benchmark.
URL:https://cmsa.fas.harvard.edu/event/12-8-21-new-technologies-in-mathematics/
LOCATION:Virtual
CATEGORIES:New Technologies in Mathematics Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-NTM-Seminar-12.08.21.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211209T093000
DTEND;TZID=America/New_York:20211209T143000
DTSTAMP:20260514T162549
CREATED:20230705T082223Z
LAST-MODIFIED:20250328T200233Z
UID:10000072-1639042200-1639060200@cmsa.fas.harvard.edu
SUMMARY:CMSA Math-Science Literature Lecture - Karen Uhlenbeck
DESCRIPTION:Karen Uhlenbeck (Institute for Advanced Study) \nTitle: The Noether Theorems in Geometry: Then and Now \nAbstract: The 1918 Noether theorems were a product of the general search for energy and momentum conservation in Einstein’s newly formulated theory of general relativity. Although widely referred to as the connection between symmetry and conservation laws\, the theorems themselves are often not understood properly and hence have not been as widely used as they might be. In the first part of the talk\, I outline a brief history of the theorems\, explain a bit of the language\, translate the first theorem into coordinate invariant language and give a few examples. I will mention only briefly their importance in physics and integrable systems. In the second part of the talk\, I describe why they are still relevant in geometric analysis: how they underlie standard techniques and why George Daskalopoulos and I came to be interested in them for our investigation into the best Lipschitz maps of Bill Thurston. Some applications to integrals on a domain a hyperbolic surface leave open possibilities for applications to integrals on domains which are locally symmetric spaces of higher dimension. The talk finishes with an example or two from the literature. \nTalk Chair: Laura DeMarco \nVIDEO
URL:https://cmsa.fas.harvard.edu/event/12-9-21-math-science-literature-lecture-karen-uhlenbeck/
LOCATION:Virtual
CATEGORIES:Event,Math Science Literature Lecture Series,Public Lecture,Special Lectures
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/Lecture_Uhlenbeck_12921.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211209T142900
DTEND;TZID=America/New_York:20211209T152900
DTSTAMP:20260514T162549
CREATED:20240215T093828Z
LAST-MODIFIED:20240215T093828Z
UID:10002723-1639060140-1639063740@cmsa.fas.harvard.edu
SUMMARY:12/9/21 Interdisciplinary Science Seminar
DESCRIPTION:Title: Numerical Higher Dimensional Geometry \nAbstract: In 1977\, Yau proved that a Kahler manifold with zero first Chern class admits a Ricci flat metric\, which is uniquely determined by certain “moduli” data. These metrics have been very important in mathematics and in theoretical physics\, but despite much subsequent work we have no analytical expressions for them. But significant progress has been made on computing numerical approximations. We give an introduction (not assuming knowledge of complex geometry) to these problems and describe these methods.
URL:https://cmsa.fas.harvard.edu/event/12-9-21-interdisciplinary-science-seminar/
LOCATION:MA
CATEGORIES:Interdisciplinary Science Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Interdisciplinary-Science-Seminar-12.09.21-1583x2048-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211210T093000
DTEND;TZID=America/New_York:20211210T103000
DTSTAMP:20260514T162549
CREATED:20240214T072023Z
LAST-MODIFIED:20240301T110742Z
UID:10002556-1639128600-1639132200@cmsa.fas.harvard.edu
SUMMARY:On the solution space of the Ising perceptron model
DESCRIPTION:Member Seminar  \nSpeaker: Changji Xu \nTitle: On the solution space of the Ising perceptron model \nAbstract:  Consider the discrete cube $\{-1\,1\}^N$ and a random collection of half spaces which includes each half space $H(x) := \{y \in \{-1\,1\}^N: x \cdot y \geq \kappa \sqrt{N}\}$ for $x \in \{-1\,1\}^N$ independently with probability $p$. The solution space is the intersection of these half spaces. In this talk\, we will talk about its sharp threshold phenomenon\, the frozen structure of the solution space\, and the Gardner formula.
URL:https://cmsa.fas.harvard.edu/event/12-10-2021-member-seminar/
LOCATION:MA
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211210T143000
DTEND;TZID=America/New_York:20211210T160000
DTSTAMP:20260514T162549
CREATED:20240214T094047Z
LAST-MODIFIED:20240301T083259Z
UID:10002642-1639146600-1639152000@cmsa.fas.harvard.edu
SUMMARY:Gravitational anomaly of 3 + 1 dimensional Z2 toric code with fermionic charges and ferionic loop self-statistics
DESCRIPTION:Speaker: Lukasz Fidkowski (U Washington) \nTitle: Gravitational anomaly of 3 + 1 dimensional Z2 toric code with fermionic charges and ferionic loop self-statistics \nAbstract: Quasiparticle excitations in 3 + 1 dimensions can be either bosons or fermions. In this work\, we introduce the notion of fermionic loop excitations in 3 + 1 dimensional topological phases. Specifically\, we construct a new many-body lattice invariant of gapped Hamiltonians\, the loop self-statistics μ = ±1\, that distinguishes two bosonic topological orders that both superficially resemble 3 + 1d Z2 gauge theory coupled to fermionic charged matter. The first has fermionic charges and bosonic Z2 gauge flux loops (FcBl) and is just the ordinary fermionic toric code. The second has fermionic charges and fermionic loops (FcFl) and\, as we argue\, can only exist at the boundary of a non-trivial 4 + 1d invertible phase\, stable without any symmetries i.e.\, it possesses a gravitational anomaly. We substantiate these claims by constructing an explicit exactly solvable 4 + 1d Walker–Wang model and computing the loop self-statistics in the fermionic Z2 gauge theory hosted at its boundary. We also show that the FcFl phase has the same gravitational anomaly as all-fermion quantum electrodynamics. Our results are in agreement with the recent classification of nondegenerate braided fusion 2- categories\, and with the cobordism prediction of a non-trivial Z2-classified 4+1d invertible phase with action S = (1/2) w2 w3.
URL:https://cmsa.fas.harvard.edu/event/12-10-2021-quantum-matter-in-mathematics-and-physics/
LOCATION:MA
CATEGORIES:Quantum Matter
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211214T093000
DTEND;TZID=America/New_York:20211214T103000
DTSTAMP:20260514T162549
CREATED:20240213T112343Z
LAST-MODIFIED:20240304T102729Z
UID:10002495-1639474200-1639477800@cmsa.fas.harvard.edu
SUMMARY:The longest induced path in a sparse random graph
DESCRIPTION:Abstract: A long-standing problem in random graph theory has been to determine asymptotically the length of a longest induced path in sparse random graphs. Independent work of Luczak and Suen from the 90s showed the existence of an induced path of roughly half the optimal size\, which seems to be a barrier for certain natural approaches. Recently\, in joint work with Draganic and Krivelevich\, we solved this problem. In the talk\, I will discuss the history of the problem and give an overview of the proof.
URL:https://cmsa.fas.harvard.edu/event/12-14-21-combinatorics-physics-and-probability-seminar/
LOCATION:MA
CATEGORIES:Combinatorics Physics and Probability
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Combinatorics-Physics-and-Probability-Seminar-12.14.2021.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211215T093000
DTEND;TZID=America/New_York:20211215T103000
DTSTAMP:20260514T162549
CREATED:20240214T042254Z
LAST-MODIFIED:20240502T154858Z
UID:10002527-1639560600-1639564200@cmsa.fas.harvard.edu
SUMMARY:The Kapustin-Rozanski-Saulina "2-category" of a holomorphic integrable system
DESCRIPTION:Speaker: Constantin Teleman (UC Berkeley) \nTitle: The Kapustin-Rozanski-Saulina “2-category” of a holomorphic integrable system \nAbstract: I will present a construction of the object in the title which\, applied to the classical Toda system\, controls the theory of categorical representations of compact Lie groups\, along with applications (some conjectural\, some rigorous) to gauged Gromov-Witten theory. Time permitting\, we will review applications to Coulomb branches and the categorified Weyl character formula.
URL:https://cmsa.fas.harvard.edu/event/the-kapustin-rozanski-saulina-2-category-of-a-holomorphic-integrable-system/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Colloquium-12.15.21-791x1024-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211215T140000
DTEND;TZID=America/New_York:20211215T150000
DTSTAMP:20260514T162549
CREATED:20230808T180208Z
LAST-MODIFIED:20240515T204057Z
UID:10001202-1639576800-1639580400@cmsa.fas.harvard.edu
SUMMARY:Unreasonable effectiveness of the quantum complexity view on quantum many-body physics
DESCRIPTION:Speaker: Anurag Anshu\, Department of EECS & Challenge Institute for Quantum Computation\, UC Berkeley \nTitle: Unreasonable effectiveness of the quantum complexity view on quantum many-body physics \nAbstract: A central challenge in quantum many-body physics is to estimate the properties of natural quantum states\, such as the quantum ground states and Gibbs states. Quantum Hamiltonian complexity offers a computational perspective on this challenge and classifies these natural quantum states using the language of quantum complexity classes. This talk will provide a gentle introduction to the field and highlight its success in pinning down the hardness of a wide variety of quantum states. In particular\, we will consider the gapped ground states and Gibbs states on low dimensional lattices\, which are believed to exhibit ‘low complexity’ due to the widely studied area law behaviour. Here\, we will see the crucial role of complexity-theoretic methods in progress on the ‘area law conjecture’ and in the development of efficient algorithms to classically simulate quantum many-body systems.
URL:https://cmsa.fas.harvard.edu/event/12-15-21-new-technologies-in-mathematics/
LOCATION:Virtual
CATEGORIES:New Technologies in Mathematics Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-NTM-Seminar-12.15.21-2.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211216T130000
DTEND;TZID=America/New_York:20211216T140000
DTSTAMP:20260514T162549
CREATED:20240214T075612Z
LAST-MODIFIED:20240304T052540Z
UID:10002573-1639659600-1639663200@cmsa.fas.harvard.edu
SUMMARY:Low regularity ill-posedness for 3D elastic waves and for 3D ideal compressible MHD driven by shock formation
DESCRIPTION:Abstract: We construct counterexamples to the local existence of low-regularity solutions to elastic wave equations and to the ideal compressible magnetohydrodynamics (MHD) system in three spatial dimensions (3D). Inspired by the recent works of Christodoulou\, we generalize Lindblad’s classic results on the scalar wave equation by showing that the Cauchy problems for 3D elastic waves and for 3D MHD system are ill-posed in $H^3(R^3)$ and $H^2(R^3)$\, respectively. Both elastic waves and MHD are physical systems with multiple wave speeds.  We further prove that the ill-posedness is caused by instantaneous shock formation\, which is characterized by the vanishing of the inverse foliation density. In particular\, when the magnetic field is absent in MHD\, we also provide a desired low-regularity ill-posedness result for the 3D compressible Euler equations\, and it is sharp with respect to the regularity of the fluid velocity.  Our proofs for elastic waves and for MHD are based on a coalition of a carefully designed algebraic approach and a geometric approach. To trace the nonlinear interactions of various waves\, we algebraically decompose the 3D elastic waves and the 3D ideal MHD equations into $6\times 6$ and $7\times 7$ non-strictly hyperbolic systems. Via detailed calculations\, we reveal their hidden subtle structures. With them\, we give a complete description of solutions’ dynamics up to the earliest singular event\, when a shock forms. This talk is based on joint works with Haoyang Chen and Silu Yin.
URL:https://cmsa.fas.harvard.edu/event/12-16-2021-general-relativity-seminar/
LOCATION:MA
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211216T144600
DTEND;TZID=America/New_York:20211216T154600
DTSTAMP:20260514T162549
CREATED:20240215T093643Z
LAST-MODIFIED:20240215T093643Z
UID:10002722-1639665960-1639669560@cmsa.fas.harvard.edu
SUMMARY:12/16/2021 Interdisciplinary Science Seminar
DESCRIPTION:Title: Quadratic reciprocity from a family of adelic conformal field theories \nAbstract: We consider a deformation of the 2d free scalar field action by raising the Laplacian to a positive real power. It turns out that the resulting non-local generalized free action is invariant under two commuting actions of the global conformal symmetry algebra\, although it’s no longer invariant under the local conformal symmetry algebra. Furthermore\, there is an adelic version of this family of global conformal field theories\, parametrized by the choice of a number field\, together with a Hecke character. Tate’s thesis plays an important role here in calculating Green’s functions of these theories\, and in ensuring the adelic compatibility of these theories. In particular\, the local L-factors contribute to prefactors of these Green’s functions. We shall try to see quadratic reciprocity from this context\, as a consequence of an adelic version of holomorphic factorization of these theories. This is work in progress with B. Stoica and X. Zhong.
URL:https://cmsa.fas.harvard.edu/event/12-16-2021-interdisciplinary-science-seminar/
LOCATION:MA
CATEGORIES:Interdisciplinary Science Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211218T090000
DTEND;TZID=America/New_York:20211231T170000
DTSTAMP:20260514T162549
CREATED:20230904T080332Z
LAST-MODIFIED:20250303T193414Z
UID:10000049-1639818000-1640970000@cmsa.fas.harvard.edu
SUMMARY:CONDENSED MATTER PROGRAM
DESCRIPTION:The methods of topology have been applied to condensed matter physics in the study of topological phases of matter. Topological states of matter are new quantum states that can be characterized by their topological properties. For example\, the first topological states of matter discovered were the integer quantum Hall states. The two dimensional integer quantum Hall effect was characterized by an integral number which can be understood as a Chern number of the Berry phase. Chern numbers are topological invariants that play an important role in different areas of mathematics. More recently\, new topological states of matter known as topological insulators and topological superconductors have been realized theoretically and experimentally. The characterization of new phases of matter using topological invariants has allowed for a better understanding and even predictions of new phases of matter. The use of topology could lead to the discovery of new electronic\, photonic\, and ultracold atomic states of matter previously unknown. The concrete problems in the physical phenomena could inspire new developments in the study of topological invariants in mathematics. \nHere is a list of the scholars participating in this program. \n\n\n\n\nName\n\n\n\n\nShing-Tung Yau\n\n\nHai Lin\n\n\nJuven Wang\n\n\nPeng Gao
URL:https://cmsa.fas.harvard.edu/event/condensed-matter-program/
LOCATION:MA
CATEGORIES:Programs
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211221T093000
DTEND;TZID=America/New_York:20211221T103000
DTSTAMP:20260514T162549
CREATED:20240213T113347Z
LAST-MODIFIED:20240304T110811Z
UID:10002505-1640079000-1640082600@cmsa.fas.harvard.edu
SUMMARY:Colloquium 2021–22
DESCRIPTION:During the 2021–22 academic year\, the CMSA will be hosting a Colloquium\, organized by Du Pei\, Changji Xu\, and Michael Simkin. It will take place on Wednesdays at 9:30am – 10:30am (Boston time). The meetings will take place virtually on Zoom. All CMSA postdocs/members are required to attend the weekly CMSA Members’ Seminars\, as well as the weekly CMSA Colloquium series. The schedule below will be updated as talks are confirmed. \nSpring 2022 \n\n\n\nDate\nSpeaker\nTitle/Abstract\n\n\n1/26/2022\nSamir Mathur (Ohio State University)\nTitle: The black hole information paradox \nAbstract: In 1975\, Stephen Hawking showed that black holes radiate away in a manner that violates quantum theory. Starting in 1997\, it was observed that black holes in string theory did not have the form expected from general relativity: in place of “empty space will all the mass at the center\,” one finds a “fuzzball” where the mass is distributed throughout the interior of the horizon. This resolves the paradox\, but opposition to this resolution came from groups who sought to extrapolate some ideas in holography. In 2009 it was shown\, using some theorems from quantum information theory\, that these extrapolations were incorrect\, and the fuzzball structure was essential for resolving the puzzle. Opposition continued along different lines\, with a postulate that information would leak out through wormholes. Recently\, it was shown that this wormhole idea had some basic flaws\, leaving the fuzzball paradigm as the natural resolution of Hawking’s puzzle. \nVideo\n\n\n2/2/2022\nAdam Smith (Boston University)\nTitle: Learning and inference from sensitive data \nAbstract: Consider an agency holding a large database of sensitive personal information—say\,  medical records\, census survey answers\, web searches\, or genetic data. The agency would like to discover and publicly release global characteristics of the data while protecting the privacy of individuals’ records. \nI will discuss recent (and not-so-recent) results on this problem with a focus on the release of statistical models. I will first explain some of the fundamental limitations on the release of machine learning models—specifically\, why such models must sometimes memorize training data points nearly completely. On the more positive side\, I will present differential privacy\, a rigorous definition of privacy in statistical databases that is now widely studied\, and increasingly used to analyze and design deployed systems. I will explain some of the challenges of sound statistical inference based on differentially private statistics\, and lay out directions for future investigation.\n\n\n2/8/2022\nWenbin Yan (Tsinghua University)\n(special time: 9:30 pm ET)\nTitle: Tetrahedron instantons and M-theory indices \nAbstract: We introduce and study tetrahedron instantons. Physically they capture instantons on $\mathbb{C}^{3}$ in the presence of the most general intersecting codimension-two supersymmetric defects. In this talk\, we will review instanton moduli spaces\, explain the construction\, moduli space and partition functions of tetrahedron instantons. We will also point out possible relations with M-theory index which could be a generalization of Gupakuma-Vafa theory. \nVideo\n\n\n2/16/2022\nTakuro Mochizuki (Kyoto University)\nTitle: Kobayashi-Hitchin correspondences for harmonic bundles and monopoles \nAbstract: In 1960’s\, Narasimhan and Seshadri discovered the equivalence\nbetween irreducible unitary flat bundles and stable bundles of degree $0$ on compact Riemann surfaces. In 1980’s\, Donaldson\, Uhlenbeck and Yau generalized it to the equivalence between irreducible Hermitian-Einstein bundles\nand stable bundles on smooth projective varieties. This is a surprising bridge connecting differential geometry and algebraic geometry. Since then\, many interesting generalizations have been studied. \nIn this talk\, we would like to review a stream in the study of such correspondences for Higgs bundles\, integrable connections\, $D$-modules and periodic monopoles.\n\n\n2/23/2022\nBartek Czech (Tsinghua University)\nTitle: Holographic Cone of Average Entropies and Universality of Black Holes \nAbstract:  In the AdS/CFT correspondence\, the holographic entropy cone\, which identifies von Neumann entropies of CFT regions that are consistent with a semiclassical bulk dual\, is currently known only up to n=5 regions. I explain that average\nentropies of p-partite subsystems can be checked for consistency with a semiclassical bulk dual far more easily\, for an arbitrary number of regions n. This analysis defines the “Holographic Cone of Average\nEntropies” (HCAE). I conjecture the exact form of HCAE\, and find that it has the following properties: (1) HCAE is the simplest it could be\, namely it is a simplicial cone. (2) Its extremal rays represent stages of thermalization (black hole formation). (3) In a time-reversed picture\, the extremal rays of HCAE represent stages of unitary black hole evaporation\, as stipulated by the island solution of the black hole information paradox. (4) HCAE is bound by a novel\, infinite family of holographic entropy inequalities. (5) HCAE is the simplest it could be also in its dependence on the number of regions n\, namely its bounding inequalities are n-independent. (6) In a precise sense I describe\, the bounding inequalities of HCAE unify (almost) all previously discovered holographic inequalities and strongly constrain future inequalities yet to be discovered. I also sketch an interpretation of HCAE in terms of error correction and the holographic Renormalization Group. The big lesson that HCAE seems to be teaching us is about the universality of black hole physics.\n\n\n3/2/2022\nRichard Kenyon (Yale University)\nTitle: Dimers and webs \nAbstract: We consider SL_n-local systems on graphs on surfaces and show how the associated Kasteleyn matrix can be used to compute probabilities of various topological events involving the overlay of n independent dimer covers (or “n-webs”). \nThis is joint work with Dan Douglas and Haolin Shi.\n\n\n3/9/2022\nYen-Hsi Richard Tsai (UT Austin)\nTitle: Side-effects of Learning from Low Dimensional Data Embedded in an Euclidean Space \nAbstract: The  low  dimensional  manifold  hypothesis  posits  that  the  data  found  in many applications\, such as those involving natural images\, lie (approximately) on low dimensional manifolds embedded in a high dimensional Euclidean space. In this setting\, a typical neural network defines a function that takes a finite number of vectors in the embedding space as input.  However\, one often needs to  consider  evaluating  the  optimized  network  at  points  outside  the  training distribution.  We analyze the cases where the training data are distributed in a linear subspace of Rd.  We derive estimates on the variation of the learning function\, defined by a neural network\, in the direction transversal to the subspace.  We study the potential regularization effects associated with the network’s depth and noise in the codimension of the data manifold.\n\n\n3/23/2022\nJoel Cohen (University of Maryland)\nTitle: Fluctuation scaling or Taylor’s law of heavy-tailed data\, illustrated by U.S. COVID-19 cases and deaths \nAbstract: Over the last century\, ecologists\, statisticians\, physicists\, financial quants\, and other scientists discovered that\, in many examples\, the sample variance approximates a power of the sample mean of each of a set of samples of nonnegative quantities. This power-law relationship of variance to mean is known as a power variance function in statistics\, as Taylor’s law in ecology\, and as fluctuation scaling in physics and financial mathematics. This survey talk will emphasize ideas\, motivations\, recent theoretical results\, and applications rather than detailed proofs. Many models intended to explain Taylor’s law assume the probability distribution underlying each sample has finite mean and variance. Recently\, colleagues and I generalized Taylor’s law to samples from probability distributions with infinite mean or infinite variance and higher moments. For such heavy-tailed distributions\, we extended Taylor’s law to higher moments than the mean and variance and to upper and lower semivariances (measures of upside and downside portfolio risk). In unpublished work\, we suggest that U.S. COVID-19 cases and deaths illustrate Taylor’s law arising from a distribution with finite mean and infinite variance. This model has practical implications. Collaborators in this work are Mark Brown\, Richard A. Davis\, Victor de la Peña\, Gennady Samorodnitsky\, Chuan-Fa Tang\, and Sheung Chi Phillip Yam.\n\n\n3/30/2022\nRob Leigh (UIUC)\nTitle: Edge Modes and Gravity \nAbstract:  In this talk I first review some of the many appearances of localized degrees of freedom — edge modes —  in a variety of physical systems. Edge modes are implicated for example in quantum entanglement and in various topological and holographic dualities. I then review recent work in which it has been realized that a careful treatment of such modes\, paying attention to relevant symmetries\, is required in order to properly understand such basic physical quantities as Noether charges. From many points of view\, it is conjectured that this physics may be pointing at basic properties of quantum spacetimes and gravity.\n\n\n4/6/2022\nJohannes Kleiner (LMU München)\nTitle: What is Mathematical Consciousness Science? \nAbstract: In the last three decades\, the problem of consciousness – how and why physical systems such as the brain have conscious experiences – has received increasing attention among neuroscientists\, psychologists\, and philosophers. Recently\, a decidedly mathematical perspective has emerged as well\, which is now called Mathematical Consciousness Science. In this talk\, I will give an introduction and overview of Mathematical Consciousness Science for mathematicians\, including a bottom-up introduction to the problem of consciousness and how it is amenable to mathematical tools and methods.\n\n\n4/13/2022\nYuri Manin (Max-Planck-Institut für Mathematik)\nTitle: Quantisation in monoidal categories and quantum operads \nAbstract: The standard definition of symmetries of a structure given on a set S (in the sense of Bourbaki) is the group of bijective maps S to S\, compatible with this structure.  But in fact\, symmetries of various structures related to storing and transmitting information (such as information spaces) are naturally embodied in various classes of loops such as Moufang loops\, – nonassociative analogs of groups. \nThe idea of symmetry as a group is closely related to classical physics\, in a very definite sense\, going back at least to Archimedes. When quantum physics started to replace classical\, it turned out that classical symmetries must also be replaced by their quantum versions\, e.g. quantum groups. \nIn this talk we explain how to define and study quantum versions of symmetries\, relevant to information theory and other contexts\n\n\n4/27/2022\nVenkatesan Guruswami (UC Berkeley)\nTitle: Long common subsequences between bit-strings and the zero-rate threshold of deletion-correcting codes \nAbstract: Suppose we transmit n bits on a noisy channel that deletes some fraction of the bits arbitrarily. What’s the supremum p* of deletion fractions that can be corrected with a binary code of non-vanishing rate? Evidently p* is at most 1/2 as the adversary can delete all occurrences of the minority bit. It was unknown whether this simple upper bound could be improved\, or one could in fact correct deletion fractions approaching 1/2. \nWe show that there exist absolute constants A and delta > 0 such that any subset of n-bit strings of size exp((log n)^A) must contain two strings with a common subsequence of length (1/2+delta)n. This immediately implies that the zero-rate threshold p* of worst-case bit deletions is bounded away from 1/2. \nOur techniques include string regularity arguments and a structural lemma that classifies bit-strings by their oscillation patterns. Leveraging these tools\, we find in any large code two strings with similar oscillation patterns\, which is exploited to find a long common subsequence. \nThis is joint work with Xiaoyu He and Ray Li.\n\n\n5/18/2022\n David Nelson (Harvard)\nTitle: Statistical Mechanics of Mutilated Sheets and Shells \nAbstract:  Understanding deformations of macroscopic thin plates and shells has a long and rich history\, culminating with the Foeppl-von Karman equations in 1904\, a precursor of general relativity characterized by a dimensionless coupling constant (the “Foeppl-von Karman number”) that can easily reach  vK = 10^7 in an ordinary sheet of writing paper.  However\, thermal fluctuations in thin elastic membranes fundamentally alter the long wavelength physics\, as exemplified by experiments that twist and bend individual atomically-thin free-standing graphene sheets (with vK = 10^13!)   A crumpling transition out of the flat phase for thermalized elastic membranes has been predicted when kT is large compared to the microscopic bending stiffness\, which could have interesting consequences for Dirac cones of electrons embedded in graphene.   It may be possible to lower the crumpling temperature for graphene to more readily accessible range by inserting a regular lattice of laser-cut perforations\, an expectation an confirmed by extensive molecular dynamics simulations.    We then move on to analyze the physics of sheets mutilated with puckers and stitches.   Puckers and stitches lead to Ising-like phase transitions riding on a background of flexural phonons\, as well as an anomalous coefficient of thermal expansion.  Finally\, we argue that thin membranes with a background curvature lead to thermalized spherical shells that must collapse beyond a critical size at room temperature\, even in the absence of an external pressure.\n\n\n\nFall 2021 \n\n\n\nDate\nSpeaker\nTitle/Abstract\n\n\n9/15/2021\nTian Yang\, Texas A&M\nTitle: Hyperbolic Geometry and Quantum Invariants \nAbstract: There are two very different approaches to 3-dimensional topology\, the hyperbolic geometry following the work of Thurston and the quantum invariants following the work of Jones and Witten. These two approaches are related by a sequence of problems called the Volume Conjectures. In this talk\, I will explain these conjectures and present some recent joint works with Ka Ho Wong related to or benefited from this relationship.\n\n\n9/29/2021\nDavid Jordan\, University of Edinburgh\nTitle: Langlands duality for 3 manifolds \nAbstract: Langlands duality began as a deep and still mysterious conjecture in number theory\, before branching into a similarly deep and mysterious conjecture of Beilinson and Drinfeld concerning the algebraic geometry of Riemann surfaces. In this guise it was given a physical explanation in the framework of 4-dimensional super symmetric quantum field theory by Kapustin and Witten.  However to this day the Hilbert space attached to 3-manifolds\, and hence the precise form of Langlands duality for them\, remains a mystery. \nIn this talk I will propose that so-called “skein modules” of 3-manifolds give natural candidates for these Hilbert spaces at generic twisting parameter Psi \, and I will explain a Langlands duality in this setting\, which we have conjectured with Ben-Zvi\, Gunningham and Safronov. \nIntriguingly\, the precise formulation of such a conjecture in the classical limit Psi=0 is still an open question\, beyond the scope of the talk.\n\n\n10/06/2021\nPiotr Sulkowski\, U Warsaw\nTitle: Strings\, knots and quivers \nAbstract: I will discuss a recently discovered relation between quivers and knots\, as well as – more generally – toric Calabi-Yau manifolds. In the context of knots this relation is referred to as the knots-quivers correspondence\, and it states that various invariants of a given knot are captured by characteristics of a certain quiver\, which can be associated to this knot. Among others\, this correspondence enables to prove integrality of LMOV invariants of a knot by relating them to motivic Donaldson-Thomas invariants of the corresponding quiver\, it provides a new insight on knot categorification\, etc. This correspondence arises from string theory interpretation and engineering of knots in brane systems in the conifold geometry; replacing the conifold by other toric Calabi-Yau manifolds leads to analogous relations between such manifolds and quivers.\n\n\n10/13/2021\nAlexei Oblomkov\, University of Massachusetts\nTitle: Knot homology and sheaves on the Hilbert scheme of points on the plane. \nAbstract: The knot homology (defined by Khovavov\, Rozansky) provide us with a refinement of the knot polynomial knot invariant defined by Jones. However\, the knot homology are much harder to compute compared to the polynomial invariant of Jones. In my talk I present recent developments that allow us to use tools of algebraic geometry to compute the homology of torus knots and prove long-standing conjecture on the Poincare duality the knot homology. In more details\, using physics ideas of Kapustin-Rozansky-Saulina\, in the joint work with Rozansky\, we provide a mathematical construction that associates to a braid on n strands a complex of sheaves on the Hilbert scheme of n points on the plane.  The knot homology of the closure of the braid is a space of sections of this sheaf. The sheaf is also invariant with respect to the natural symmetry of the plane\, the symmetry is the geometric counter-part of the mentioned Poincare duality.\n\n\n10/20/2021\nPeng Shan\, Tsinghua U\nTitle: Categorification and applications \nAbstract: I will give a survey of the program of categorification for quantum groups\, some of its recent development and applications to representation theory.\n\n\n10/27/2021\nKarim Adiprasito\, Hebrew University and University of Copenhagen\nTitle: Anisotropy\, biased pairing theory and applications \nAbstract: Not so long ago\, the relations between algebraic geometry and combinatorics were strictly governed by the former party\, with results like log-concavity of the coefficients of the characteristic polynomial of matroids shackled by intuitions and techniques from projective algebraic geometry\, specifically Hodge Theory. And so\, while we proved analogues for these results\, combinatorics felt subjugated to inspirations from outside of it.\nIn recent years\, a new powerful technique has emerged: Instead of following the geometric statements of Hodge theory about signature\, we use intuitions from the Hall marriage theorem\, translated to algebra: once there\, they are statements about self-pairings\, the non-degeneracy of pairings on subspaces to understand the global geometry of the pairing. This was used to establish Lefschetz type theorems far beyond the scope of algebraic geometry\, which in turn established solutions to long-standing conjectures in combinatorics. \nI will survey this theory\, called biased pairing theory\, and new developments within it\, as well as new applications to combinatorial problems. Reporting on joint work with Stavros Papadaki\, Vasiliki Petrotou and Johanna Steinmeyer.\n\n\n11/03/2021\nTamas Hausel\, IST Austria\nTitle: Hitchin map as spectrum of equivariant cohomology \nAbstract: We will explain how to model the Hitchin integrable system on a certain Lagrangian upward flow as the spectrum of equivariant cohomology of a Grassmannian.\n\n\n11/10/2021\nPeter Keevash\, Oxford\nTitle: Hypergraph decompositions and their applications\n\nAbstract: Many combinatorial objects can be thought of as a hypergraph decomposition\, i.e. a partition of (the edge set of) one hypergraph into (the edge sets of) copies of some other hypergraphs. For example\, a Steiner Triple System is equivalent to a decomposition of a complete graph into triangles. In general\, Steiner Systems are equivalent to decompositions of complete uniform hypergraphs into other complete uniform hypergraphs (of some specified sizes). The Existence Conjecture for Combinatorial Designs\, which I proved in 2014\, states that\, bar finitely many exceptions\, such decompositions exist whenever the necessary ‘divisibility conditions’ hold. I also obtained a generalisation to the quasirandom setting\, which implies an approximate formula for the number of designs; in particular\, this resolved Wilson’s Conjecture on the number of Steiner Triple Systems. A more general result that I proved in 2018 on decomposing lattice-valued vectors indexed by labelled complexes provides many further existence and counting results for a wide range of combinatorial objects\, such as resolvable designs (the generalised form of Kirkman’s Schoolgirl Problem)\, whist tournaments or generalised Sudoku squares. In this talk\, I plan to review this background and then describe some more recent and ongoing applications of these results and developments of the ideas behind them.\n\n\n11/17/2021\nAndrea Brini\, U Sheffield\nTitle: Curve counting on surfaces and topological strings \nAbstract: Enumerative geometry is a venerable subfield of Mathematics\, with roots dating back to Greek Antiquity and a present inextricably linked with developments in other domains. Since the early 90s\, in particular\, the interaction with String Theory has sent shockwaves through the subject\, giving both unexpected new perspectives and a remarkably powerful\, physics-motivated toolkit to tackle several traditionally hard questions in the field.\nI will survey some recent developments in this vein for the case of enumerative invariants associated to a pair (X\, D)\, with X a complex algebraic surface and D a singular anticanonical divisor in it. I will describe a surprising web of correspondences linking together several a priori distant classes of enumerative invariants associated to (X\, D)\, including the log Gromov-Witten invariants of the pair\, the Gromov-Witten invariants of an associated higher dimensional Calabi-Yau variety\, the open Gromov-Witten invariants of certain special Lagrangians in toric Calabi–Yau threefolds\, the Donaldson–Thomas theory of a class of symmetric quivers\, and certain open and closed Gopakumar-Vafa-type invariants. I will also discuss how these correspondences can be effectively used to provide a complete closed-form solution to the calculation of all these invariants.\n\n\n12/01/2021\nRichard Wentworth\, University of Maryland\nTitle: The Hitchin connection for parabolic G-bundles \nAbstract: For a simple and simply connected complex group G\, I will discuss some elements of the proof of the existence of a flat projective connection on the bundle of nonabelian theta functions on the moduli space of semistable parabolic G-bundles over families of smooth projective curves with marked points. Under the isomorphism with the bundle of conformal blocks\, this connection is equivalent to the one constructed by conformal field theory. This is joint work with Indranil Biswas and Swarnava Mukhopadhyay.\n\n\n12/08/2021\nMaria Chudnovsky\, Princeton\nTitle: Induced subgraphs and tree decompositions \nAbstract: Tree decompositions are a powerful tool in both structural\ngraph theory and graph algorithms. Many hard problems become tractable if the input graph is known to have a tree decomposition of bounded “width”. Exhibiting a particular kind of a tree decomposition is also a useful way to describe the structure of a graph. \nTree decompositions have traditionally been used in the context of forbidden graph minors; bringing them into the realm of forbidden induced subgraphs has until recently remained out of reach. Over the last couple of years we have made significant progress in this direction\, exploring both the classical notion of bounded tree-width\, and concepts of more structural flavor. This talk will survey some of these ideas and results.\n\n\n12/15/21\nConstantin Teleman (UC Berkeley)\nTitle: The Kapustin-Rozanski-Saulina “2-category” of a holomorphic integrable system \nAbstract: I will present a construction of the object in the title which\, applied to the classical Toda system\, controls the theory of categorical representations of compact Lie groups\, along with applications (some conjectural\, some rigorous) to gauged Gromov-Witten theory. Time permitting\, we will review applications to Coulomb branches and the categorified Weyl character formula.
URL:https://cmsa.fas.harvard.edu/event/colloquium-2021-22/
LOCATION:MA
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220106T090000
DTEND;TZID=America/New_York:20220106T100000
DTSTAMP:20260514T162549
CREATED:20240215T093525Z
LAST-MODIFIED:20240529T175141Z
UID:10002721-1641459600-1641463200@cmsa.fas.harvard.edu
SUMMARY:The smooth closing lemma for area-preserving surface diffeomorphisms
DESCRIPTION:Speaker: Boyu Zhang\, Princeton University \nTitle: The smooth closing lemma for area-preserving surface diffeomorphisms \nAbstract: In this talk\, I will introduce the smooth closing lemma for area-preserving diffeomorphisms on surfaces. The proof is based on a Weyl formula for PFH spectral invariants and a non-vanishing result of twisted Seiberg- Witten Floer homology. This is joint work with Dan Cristofaro-Gardiner and Rohil Prasad.
URL:https://cmsa.fas.harvard.edu/event/1-6-2022-interdisciplinary-science-seminar/
LOCATION:Virtual
CATEGORIES:Interdisciplinary Science Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Interdisciplinary-Science-Seminar-01.06.22.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220114T093000
DTEND;TZID=America/New_York:20220114T103000
DTSTAMP:20260514T162549
CREATED:20240214T090947Z
LAST-MODIFIED:20240301T112406Z
UID:10002609-1642152600-1642156200@cmsa.fas.harvard.edu
SUMMARY:Light strings\, strong coupling\, and the Swampland
DESCRIPTION:Member Seminar \nSpeaker: Max Wiesner\n\nTitle: Light strings\, strong coupling\, and the Swampland \nAbstract: In this talk\, I will start by reviewing central ideas of the so-called Swampland Program. The Swampland Program aims to identify criteria that distinguish low-energy effective field theories\, that can be consistently coupled to quantum gravity\, from those theories that become inconsistent in the presence of quantum gravity. \nIn my talk I will specialize to four-dimensional effective field theories with N=2 and N=1 supersymmetry. In weakly-coupled regions of the scalar field space of such theories\, it has been shown that light strings are crucial to realize certain Swampland criteria. Complementary to that\, the focus of this talk will be on the role of such light strings away from these weak-coupling regimes. In this context\, I will first discuss a relation between light perturbative strings and strong coupling singularities in the Kähler moduli space of 4d N=1 compactifications of F-theory. More precisely\, in regions of moduli space\, in which a critical string classically becomes light\, I will show that non-perturbative corrections yield to strong coupling singularities for D7-brane gauge theories which obstruct weak-coupling limits. Moreover\, I will demonstrate that in the vicinity of this strong coupling singularity\, the critical\, light string in fact leaves the spectrum of BPS strings thereby providing an explanation for the obstruction of the weak coupling limit. \nI will then move on and discuss the backreaction of perturbative strings in 4d EFTs. Away from the string core\, the backreaction of such strings necessarily leads to strong coupling regions where naively the energy stored in the backreaction diverges. I will show how the introduction of additional non-critical strings can regulate this backreaction and how this can be used to study the spectrum of BPS strings and their tensions even beyond weak coupling regions. In this context\, I will demonstrate how the requirement\, that the total string tension should not exceed the Planck scale\, constrains the possible BPS string charges.
URL:https://cmsa.fas.harvard.edu/event/1-14-2022-member-seminar/
LOCATION:MA
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220118T143000
DTEND;TZID=America/New_York:20220118T160000
DTSTAMP:20260514T162549
CREATED:20240214T092207Z
LAST-MODIFIED:20240301T075905Z
UID:10002620-1642516200-1642521600@cmsa.fas.harvard.edu
SUMMARY:Metals with strongly correlated electrons: quantum criticality\, disordered interactions\, Planckian dissipation\, and scale invariance
DESCRIPTION:Speaker: Aavishkar Patel (UC Berkeley) \nTitle: Metals with strongly correlated electrons: quantum criticality\, disordered interactions\, Planckian dissipation\, and scale invariance \nAbstract: Metals that do not fit Landau’s famous Fermi liquid paradigm of quasiparticles are plentiful in experiments\, but constructing their theoretical description is a major challenge in modern quantum many-body physics. I will describe new models that can systematically describe such non-Fermi liquid metals at quantum critical points\, and that allow for the accurate computation of a whole host of experimentally measurable static and dynamic quantities despite the presence of both strong correlations and disorder. I will further demonstrate that disorder coupling to interaction operators can lead to the experimentally observed linear-in-temperature (T-linear) resistivity seen at metallic quantum critical points\, and can also generate the observed universal “Planckian” transport scattering rate of kBT/ℏ. Finally\, I will show that “perfect” T-linear resistivity is associated with an energy invariant quantity defined in the many-body microcanonical ensemble\, which motivates the existence of a deep connection between the T-linear resistivity seen at high temperatures and low temperatures with the same slope in many quantum critical materials.
URL:https://cmsa.fas.harvard.edu/event/1-18-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:MA
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-1.18.22-1544x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220120T145200
DTEND;TZID=America/New_York:20220120T165200
DTSTAMP:20260514T162549
CREATED:20240215T093039Z
LAST-MODIFIED:20240215T093039Z
UID:10002719-1642690320-1642697520@cmsa.fas.harvard.edu
SUMMARY:1/20/2022 – Interdisciplinary Science Seminar
DESCRIPTION:Title: Markov chains\, optimal control\, and reinforcement learning \nAbstract: Markov decision processes are a model for several artificial intelligence problems\, such as games (chess\, Go…) or robotics. At each timestep\, an agent has to choose an action\, then receives a reward\, and then the agent’s environment changes (deterministically or stochastically) in response to the agent’s action. The agent’s goal is to adjust its actions to maximize its total reward. In principle\, the optimal behavior can be obtained by dynamic programming or optimal control techniques\, although practice is another story. \nHere we consider a more complex problem: learn all optimal behaviors for all possible reward functions in a given environment. Ideally\, such a “controllable agent” could be given a description of a task (reward function\, such as “you get +10 for reaching here but -1 for going through there”) and immediately perform the optimal behavior for that task. This requires a good understanding of the mapping from a reward function to the associated optimal behavior. \nWe prove that there exists a particular “map” of a Markov decision process\, on which near-optimal behaviors for all reward functions can be read directly by an algebraic formula. Moreover\, this “map” is learnable by standard deep learning techniques from random interactions with the environment. We will present our recent theoretical and empirical results in this direction.
URL:https://cmsa.fas.harvard.edu/event/1-20-2022-interdisciplinary-science-seminar/
LOCATION:MA
CATEGORIES:Interdisciplinary Science Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Interdisciplinary-Science-Seminar-01.20.22-1577x2048-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220121T093000
DTEND;TZID=America/New_York:20220121T103000
DTSTAMP:20260514T162549
CREATED:20240214T090725Z
LAST-MODIFIED:20240301T112306Z
UID:10002607-1642757400-1642761000@cmsa.fas.harvard.edu
SUMMARY:AdS with Scale Separation
DESCRIPTION:Member Seminar \nSpeaker: Daniel Junghans\n\nTitle: AdS with Scale Separation \nAbstract: I will talk about Anti-de Sitter solutions in string theory with a parametric separation between the AdS curvature scale and the Kaluza-Klein scale. In particular\, I will discuss recent progress on computing backreaction corrections in such solutions\, and I will explain how to construct solutions without Romans mass that can be lifted to M-theory.
URL:https://cmsa.fas.harvard.edu/event/1-21-2022-member-seminar/
LOCATION:MA
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220124T090000
DTEND;TZID=America/New_York:20220521T170000
DTSTAMP:20260514T162549
CREATED:20230904T083438Z
LAST-MODIFIED:20240215T103430Z
UID:10000055-1643014800-1653152400@cmsa.fas.harvard.edu
SUMMARY:General Relativity Program
DESCRIPTION:During the Spring 2022 semester\, the CMSA hosted a program on General Relativity. \nThis semester-long program included four minicourses\,  a conference\, and a workshop. \nGeneral Relativity Mincourses: March–May\, 2022 \nGeneral Relativity Conference: April 4–8\, 2022 \nGeneral Relativity Workshop: May 2–5\, 2022 \n  \nProgram Visitors \n\nDan Lee\, CMSA/CUNY\, 1/24/22 – 5/20/22\nStefan Czimek\, Brown\, 2/27/22 – 3/3/22\nLan-Hsuan Huang\, University of Connecticut\, 3/13/22 – 3/19/222\, 3/21/22 – 3/25/22\, 4/17 /22– 4/23/22\nMu-Tao Wang\, Columbia\, 3/21/22 – 3/25/22\, 5/7/22 – 5/9/22\nPo-Ning Chen\, University of California\, Riverside\, 3/21/22 – 3/25/22\,  5/7/22–5/9/22\nMarnie Smith\, Imperial College London\, 3/27/22 – 4/11/22\nChristopher Stith\, University of Michigan\, 3/27/22 – 4/23/22\nMartin Taylor\, Imperial College London\,  3/27/22 – 4/11/22\nMarcelo Disconzi\, Vanderbilt\, 5/9/22 – 5/21/22\nLydia Bieri\, University of Michigan\, 5/5/22 – 5/9/22\n\n 
URL:https://cmsa.fas.harvard.edu/event/general-relativity-program/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Event,Programs
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/GR-Program-Banner_800x450-2.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220125T013000
DTEND;TZID=America/New_York:20220125T150000
DTSTAMP:20260514T162549
CREATED:20240213T102636Z
LAST-MODIFIED:20240213T102636Z
UID:10002425-1643074200-1643122800@cmsa.fas.harvard.edu
SUMMARY:11/7/2018 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/11-7-2018-hodge-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
END:VCALENDAR