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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180125T142100
DTEND;TZID=America/New_York:20180125T142100
DTSTAMP:20240213T103415Z
CREATED:20240213T103415Z
LAST-MODIFIED:20240213T103415Z
UID:10002441-1516890060-1516890060@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Quantum Cohomology\, Nakajima Varieties and Quantum groups
DESCRIPTION:During the Spring 2018 Semester Artan Sheshmani (QGM/CMSA) will be teaching a CMSA special lecture series on Quantum Cohomology\, Nakajima Vareties and Quantum groups. The lectures will be held Tuesdays and Thursdays beginning January 25th\, from 1:00 to 3:00pm in room G10\, CMSA Building. \nYou can watch Prof. Sheshmani describe the series here. \nThe Syllabus is as follows: \n\n\n\nDate………..\nTopic\nVideo/Audio\n\n\n1-25-2018\nGromov-Witten invariants  \nDefinition\, examples via algebraic geometry I\nVideo / Audio / Combined  \n\n*due to technical difficulties the audio and video are split for this lecture.\n\n\n 2-01-2018\nGromov-Witten invariants  \nVirtual Fundamental Class I (definition)\nVideo / Audio / Combined  \n\n*due to technical difficulties the audio and video are split for this lecture\n\n\n2-13-2018\nGromov-Witten invariants  \nVirtual Fundamental Class II (computation in some cases)\n\n\n\n 2-15-2018\nComputing GW invariants  \nThree level GW classes \nGenus zero invariants of the projective plane\n\n\n\n 2-20-2018\nQuantum Cohomology  \nSmall Quantum Cohomology (Definition and Properties) I\n\n\n\n2-22-2018\nQuantum Cohomology  \nSmall Quantum Cohomology (Definition and Properties) II\n\n\n\n2-27-2018\nQuantum Cohomology  \nBig Quantum Cohomology I\n\n\n\n 3-1-2018\nQuantum Cohomology  \nBig Quantum Cohomology II \nGW potential \nWDVV equation\n\n\n\n3-6-2018\nGW invariants via Quantum Cohomology  \nThe Quintic threefold case \nThe P^2 case\n\n\n\n\nGW invariants via Quantum Cohomology  \nDubrovin (quantum) connection\n\n\n\n\nNakajima varieties  \n-Algebraic and symplectic reduction\n\n\n\n\nNakajima varieties  \nQuasi maps to Nakajima varieties\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nSmall Quantum Cohomology of Hilb^n (C2) I\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nSmall Quantum Cohomology of Hilb^n (C2) II\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nSmall Quantum Cohomology of Hilb^n (C2) III\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nBig Quantum Cohomology of Hilb^n (C2) I\n \n\n\n\nQuantum cohomology of Nakajima varieties  \nBig Quantum Cohomology of Hilb^n (C2) II\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nBig Quantum Cohomology of Hilb^n (C2) III\n\n\n\n\nQuantum cohomology of Nakajima varieties  \nBig Quantum Cohomology of Hilb^n (C2) IV\n 
URL:https://live-hu-cmsa-222.pantheonsite.io/event/quantum-cohomology-nakajima-varieties-and-quantum-groups/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180126T143700
DTEND;TZID=America/New_York:20180126T143700
DTSTAMP:20240213T102934Z
CREATED:20240213T102934Z
LAST-MODIFIED:20240213T102934Z
UID:10002431-1516977420-1516977420@live-hu-cmsa-222.pantheonsite.io
SUMMARY:01-26-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/01-26-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180202T144400
DTEND;TZID=America/New_York:20180202T144400
DTSTAMP:20240213T102555Z
CREATED:20240213T102555Z
LAST-MODIFIED:20240213T102555Z
UID:10002423-1517582640-1517582640@live-hu-cmsa-222.pantheonsite.io
SUMMARY:2-2-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-2-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180208T170000
DTEND;TZID=America/New_York:20180208T180000
DTSTAMP:20240515T181311Z
CREATED:20240213T062806Z
LAST-MODIFIED:20240515T181311Z
UID:10002110-1518109200-1518112800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Sequences: random\, structured or something in between
DESCRIPTION:Speaker: Fan Chung (University of California\, San Diego) \nTitle: Sequences: random\, structured or something in between \nAbstract: There are many fundamental problems concerning sequences that arise in many areas of mathematics and computation. Typical problems include finding or avoiding patterns; testing or validating various ‘random-like’ behavior; analyzing or comparing different statistics\, etc. In this talk\, we will examine various notions of regularity or irregularity for sequences and mention numerous open problems. \n 
URL:https://live-hu-cmsa-222.pantheonsite.io/event/02-08-2018-colloquium/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-020818-e1518025233926.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180209T110000
DTEND;TZID=America/New_York:20180209T110000
DTSTAMP:20240213T102158Z
CREATED:20240213T102158Z
LAST-MODIFIED:20240213T102158Z
UID:10002416-1518174000-1518174000@live-hu-cmsa-222.pantheonsite.io
SUMMARY:02-09-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/02-09-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180214T163000
DTEND;TZID=America/New_York:20180214T173000
DTSTAMP:20240515T180124Z
CREATED:20240213T063118Z
LAST-MODIFIED:20240515T180124Z
UID:10002113-1518625800-1518629400@live-hu-cmsa-222.pantheonsite.io
SUMMARY:A new program on quantum subgroups
DESCRIPTION:Speaker: Zhengwei Liu (Harvard Physics) \nTitle: A new program on quantum subgroups \nAbstract: Quantum subgroups have been studied since the 1980s. The A\, D\, E classification of subgroups of quantum SU(2) is a quantum analogue of the McKay correspondence. It turns out to be related to various areas in mathematics and physics. Inspired by the quantum McKay correspondence\, we introduce a new program that our group at Harvard is developing. \n 
URL:https://live-hu-cmsa-222.pantheonsite.io/event/02-14-2018-colloqium/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-021418-e1518126484875.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180216T110000
DTEND;TZID=America/New_York:20180216T110000
DTSTAMP:20240213T101018Z
CREATED:20240213T101018Z
LAST-MODIFIED:20240213T101018Z
UID:10002397-1518778800-1518778800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:2-16-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-16-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180221T163000
DTEND;TZID=America/New_York:20180221T173000
DTSTAMP:20240515T175648Z
CREATED:20240213T063335Z
LAST-MODIFIED:20240515T175648Z
UID:10002115-1519230600-1519234200@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Essential concepts of Causal inference—a remarkable history
DESCRIPTION:Speaker: Don Rubin (Harvard Statistics) \nTitle: Essential concepts of Causal inference—a remarkable history \nAbstract: I believe that a deep understanding of cause and effect\, and how to estimate causal effects from data\, complete with the associated mathematical notation and expressions\, only evolved in the twentieth century.  The crucial idea of randomized experiments was apparently first proposed in 1925 in the context of agricultural field trails but quickly moved to be applied also in studies of animal breeding and then in industrial manufacturing.  The conceptual understanding seemed to be tied to ideas that were developing in quantum mechanics.  The key ideas of randomized experiments evidently were not applied to studies of human beings until the 1950s\, when such experiments began to be used in controlled medical trials\, and then in social science — in education and economics.  Humans are more complex than plants and animals\, however\, and with such trials came the attendant complexities of non-compliance with assigned treatment and the occurrence of “hawthorne” and placebo effects.  The formal application of the insights from earlier simpler experimental settings to more complex ones dealing with people\, started in the 1970s and continue to this day\, and include the bridging of classical mathematical ideas of experimentation\, including fractional replication and geometrical formulations from the early twentieth century\, with modern ideas that rely on powerful computing to implement aspects of design and analysis. \n 
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-21-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-022118-e1518810758992.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180223T100000
DTEND;TZID=America/New_York:20180223T110000
DTSTAMP:20240213T100016Z
CREATED:20240213T100016Z
LAST-MODIFIED:20240213T100016Z
UID:10002377-1519380000-1519383600@live-hu-cmsa-222.pantheonsite.io
SUMMARY:2-23-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-23-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180226T163000
DTEND;TZID=America/New_York:20180226T173000
DTSTAMP:20240515T175404Z
CREATED:20240213T063608Z
LAST-MODIFIED:20240515T175404Z
UID:10002119-1519662600-1519666200@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Computer-assisted analysis of singularity formation of a regularized 3D Euler equation
DESCRIPTION:Speaker: Tom Hou\, Caltech \nTitle: Computer-assisted analysis of singularity formation of a regularized 3D Euler equation \n 
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-26-2018-colloquium/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-022618-e1519319166314.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180227T150000
DTEND;TZID=America/New_York:20180227T160000
DTSTAMP:20240213T100343Z
CREATED:20240213T100343Z
LAST-MODIFIED:20240213T100343Z
UID:10002386-1519743600-1519747200@live-hu-cmsa-222.pantheonsite.io
SUMMARY:2-27-2018 HMS Lecture
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-27-2018-hms-lecture/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180302T110000
DTEND;TZID=America/New_York:20180302T120000
DTSTAMP:20240213T095700Z
CREATED:20240213T095700Z
LAST-MODIFIED:20240213T095700Z
UID:10002372-1519988400-1519992000@live-hu-cmsa-222.pantheonsite.io
SUMMARY:3-2-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/3-2-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180307T163000
DTEND;TZID=America/New_York:20180307T173000
DTSTAMP:20240515T175119Z
CREATED:20240213T063843Z
LAST-MODIFIED:20240515T175119Z
UID:10002121-1520440200-1520443800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Harmonic functions and the chromatic polynomial
DESCRIPTION:Speaker: Richard Kenyon\, Brown \nTitle: Harmonic functions and the chromatic polynomial
URL:https://live-hu-cmsa-222.pantheonsite.io/event/2-7-2018-colloquium/
LOCATION:MA
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-030718-e1520356183643.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180315T150000
DTEND;TZID=America/New_York:20180315T160000
DTSTAMP:20240213T100209Z
CREATED:20240213T100139Z
LAST-MODIFIED:20240213T100209Z
UID:10002381-1521126000-1521129600@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Dmytro Shklyrov HMS Focused Lecture Series
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/dmytro-shklyrov-hms-focused-lecture-series/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180328T163000
DTEND;TZID=America/New_York:20180328T173000
DTSTAMP:20240515T174531Z
CREATED:20240213T064501Z
LAST-MODIFIED:20240515T174531Z
UID:10002125-1522254600-1522258200@live-hu-cmsa-222.pantheonsite.io
SUMMARY:A Mean Field View of the Landscape of Two-Layers Neural Networks
DESCRIPTION:Speaker: Andrea Montanari (Stanford) \nTitle: A Mean Field View of the Landscape of Two-Layers Neural Networks \nAbstract: Multi-layer neural networks are among the most powerful models in machine learning and yet\, the fundamental reasons for this success defy mathematical understanding. Learning a neural network requires to optimize a highly non-convex and high-dimensional objective (risk function)\, a problem which is usually attacked using stochastic gradient descent (SGD). Does SGD converge to a global optimum of the risk or only to a local optimum? In the first case\, does this happen because local minima are absent\, or because SGD somehow avoids them? In the second\, why do local minima reached by SGD have good generalization properties? We consider a simple case\, namely two-layers neural networks\, and prove that –in a suitable scaling limit– the SGD dynamics is captured by a certain non-linear partial differential equation. We then consider several specific examples\, and show how the asymptotic description can be used to prove convergence of SGD to network with nearly-ideal generalization error. This description allows to ‘average-out’ some of the complexities of the landscape of neural networks\, and can be used to capture some important variants of SGD as well. [Based on joint work with Song Mei and Phan-Minh Nguyen]
URL:https://live-hu-cmsa-222.pantheonsite.io/event/3-28-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-032818-e1521831836462-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180404T163000
DTEND;TZID=America/New_York:20180404T163000
DTSTAMP:20240515T174223Z
CREATED:20240213T064751Z
LAST-MODIFIED:20240515T174223Z
UID:10002129-1522859400-1522859400@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Black Holes and Naked Singularities
DESCRIPTION:Speaker: Ramesh Narayan\, Department of Astronomy\, Harvard University \nTitle: Black Holes and Naked Singularities \nAbstract: Black Hole solutions in General Relativity contain Event Horizons and Singularities. Astrophysicists have discovered two populations of black hole candidates in the Universe: stellar-mass objects with masses in the range 5 to 30 solar masses\, and supermassive objects with masses in the range million to several billion solar masses. There is considerable evidence that these objects have Event Horizons. It thus appears that astronomical black hole candidates are true Black Holes. Direct evidence for Singularities is much harder to obtain since\, at least in the case of Black Holes\, the Singularities are hidden inside the Event Horizon. However\, General Relativity also permits Naked Singularities which are visible to external observers. Toy Naked Singularity models have been constructed\, and some observational features of accretion flows in these spacetimes have been worked out.
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-4-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/CMSA-Colloquium-040418-e1522340269661.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180411T163000
DTEND;TZID=America/New_York:20180411T173000
DTSTAMP:20240515T144439Z
CREATED:20240213T065052Z
LAST-MODIFIED:20240515T144439Z
UID:10002134-1523464200-1523467800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Graph Structure in Polynomial Systems: Chordal Networks
DESCRIPTION:Speaker: Pablo Parillo (MIT) \nTitle: Graph Structure in Polynomial Systems: Chordal Networks \nAbstract: The sparsity structure of a system of polynomial equations or an optimization problem can be naturally described by a graph summarizing the interactions among the decision variables. It is natural to wonder whether the structure of this graph might help in computational algebraic geometry tasks (e.g.\, in solving the system). In this lecture we will provide a gentle introduction to this area\, focused on the key notions of chordality and treewidth\, which are of great importance in related areas such as numerical linear algebra\, database theory\, constraint satisfaction\, and graphical models. In particular\, we will discuss “chordal networks”\, a novel representation of structured polynomial systems that provides a computationally convenient decomposition of a polynomial ideal into simpler (triangular) polynomial sets\, while maintaining its underlying graphical structure. As we will illustrate through examples from different application domains\, algorithms based on chordal networks can significantly outperform existing techniques. Based on joint work with Diego Cifuentes (MIT).
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-11-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/2018_04_10_09_58_15-e1523369654177.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180413T110000
DTEND;TZID=America/New_York:20180413T120000
DTSTAMP:20240213T101255Z
CREATED:20240213T101255Z
LAST-MODIFIED:20240213T101255Z
UID:10002403-1523617200-1523620800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:4-13-2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-13-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180413T163000
DTEND;TZID=America/New_York:20180413T173000
DTSTAMP:20240514T185400Z
CREATED:20240213T065558Z
LAST-MODIFIED:20240514T185400Z
UID:10002143-1523637000-1523640600@live-hu-cmsa-222.pantheonsite.io
SUMMARY:On the fibration structure of known Calabi-Yau threefolds
DESCRIPTION:Speaker: Washington Tayor (MIT) \nTitle: On the fibration structure of known Calabi-Yau threefolds \nAbstract: In recent years\, there is increasing evidence from a variety of directions\, including the physics of F-theory and new generalized CICY constructions\, that a large fraction of known Calabi-Yau manifolds have a genus one or elliptic fibration. In this talk I will describe recent work with Yu-Chien Huang on a systematic analysis of the fibration structure of known toric hypersurface Calabi-Yau threefolds. Among other results\, this analysis shows that every known Calabi-Yau threefold with either Hodge number exceeding 150 is genus one or elliptically fibered\, and suggests that the fraction of Calabi-Yau threefolds that are not genus one or elliptically fibered decreases roughly exponentially with h_{11}. I will also make some comments on the connection with the structure of triple intersection numbers in Calabi-Yau threefolds.
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-18-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://live-hu-cmsa-222.pantheonsite.io/media/2018_04_13_11_01_32-e1523633302205.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180416T171600
DTEND;TZID=America/New_York:20180416T171600
DTSTAMP:20240213T101737Z
CREATED:20240213T101737Z
LAST-MODIFIED:20240213T101737Z
UID:10002409-1523898960-1523898960@live-hu-cmsa-222.pantheonsite.io
SUMMARY:4-16-2018 Social Science Applications Forum
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-16-2018-social-science-applications-forum/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180417T120000
DTEND;TZID=America/New_York:20180417T133000
DTSTAMP:20240213T100938Z
CREATED:20240213T100552Z
LAST-MODIFIED:20240213T100938Z
UID:10002389-1523966400-1523971800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:4-17-2018 Special Algebraic Geometry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-17-2018-special-algebraic-geometry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180420T171800
DTEND;TZID=America/New_York:20180420T171800
DTSTAMP:20240213T101921Z
CREATED:20240213T101921Z
LAST-MODIFIED:20240213T101921Z
UID:10002412-1524244680-1524244680@live-hu-cmsa-222.pantheonsite.io
SUMMARY:4-20-2018 Social Science Applications Forum
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/4-20-2018-social-science-applications-forum/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180829T173600
DTEND;TZID=America/New_York:20180829T173600
DTSTAMP:20240213T102633Z
CREATED:20240213T102633Z
LAST-MODIFIED:20240213T102633Z
UID:10002424-1535564160-1535564160@live-hu-cmsa-222.pantheonsite.io
SUMMARY:Topological Aspects of Condensed Matter Seminar
DESCRIPTION:As part of the Program on Topological Aspects of Condensed Matter\, a weekly seminar will be held on Mondays from 10:00-11:30pm in CMSA room G10. \n\n\n\nDate\nSpeaker\nTitle/Abstract\n\n\n8/29/2018\nZeng-Cheng Gu\nTitle: Towards a complete classification of symmetry protected topological phases for interacting fermions in three dimensions and a general group supercohomology theory \nAbstract: Classification and construction of symmetry protected topological (SPT) phases in interacting boson and fermion systems have become a fascinating theoretical direction in recent years. It has been shown that the (generalized) group cohomology theory or cobordism theory can give rise to a complete classification of SPT phases in interacting boson/spin systems. Nevertheless\, the construction and classification of SPT phases in interacting fermion systems are much more complicated\, especially in 3D. In this talk\, I will revisit this problem based on the equivalent class of fermionic symmetric local unitary (FSLU) transformations. I will show how to construct very general fixed point SPT wavefunctions for interacting fermion systems. I will also discuss the procedure of deriving a general group super-cohomology theory in arbitrary dimensions.\n\n\n9/10/2018\nDominic Else\, MIT \nVideo\nTitle: Phases and topology in periodically driven (Floquet) systems \nAbstract: I will give a pedagogical overview of new topological phenomena that occur in systems that are driven periodically in time (Floquet systems). As a warm-up\, I will review new topological invariants in free-fermion Floquet systems. Then\, I will discuss the richer physics that occurs in interacting Floquet phases\, stabilized in systems with strong quenched disorder by many-body-localization (MBL). Finally\, time permitting\, I will explain how to realize interacting topological phenomena in a metastable (“pre-thermal”) regime of a clean system.\n\n\n9/17/2018\nAdrian Po\, MIT \nVideo\nTitle: A modern solution to the old problem of symmetries in band theory \nAbstract: There are 230 space groups and 1\,651 magnetic space groups in three dimensions. Thankfully\, these are finite numbers\, and one might go about solving all the possible ways free electrons represent them. This is a central question in the nine-decade-old band theory\, which is long-thought to be solvable if only one had the time and patience to crank through all the cases. In this talk\, I would describe how this problem can be solved efficiently from the modern perspective of band topology. As a by-product\, we will describe a simple method to detect topologically nontrivial band insulators using only symmetry eigenvalues\, which offers great computational advantage compared to the traditional\, wave-function-based definitions of topological band invariants.\n\n\n9/24/2018\nMaxim Metlitski\nTitle: Surface Topological Order and a new ‘t Hooft Anomaly of Interaction Enabled 3+1D Fermion SPTs \nAbstract: Symmetry protected topological (SPT) phases have attracted a lot of attention in recent years. A key property of SPTs is the presence of non-trivial surface states. While for 1+1D and 2+1D SPTs the boundary must be either symmetry broken or gapless\, some 3+1D SPTs admit symmetric gapped surface states that support anyon excitation (intrinsic topological order). In all cases\, the boundary of an SPT is anomalous – it cannot be recreated without the bulk; furthermore\, the anomaly must “match” the bulk. I will review this bulk-boundary correspondence for 3d SPT phases of bosons with topologically ordered boundaries where it is fairly well understood. I will then proceed to describe recent advances in the understanding of strongly interacting 3+1D SPT phases of fermions and their topologically ordered surface states.\n\n\n10/1/2018\nCancelled\n\n\n\n10/9/2018 \nTuesday \n3:00-4:30pm\nSagar Vijay\nTitle: Fracton Phases of Matter \nAbstract:  Fracton phases are new kinds of highly-entangled quantum matter in three spatial dimensions that are characterized by gapped\, point-like excitations (“fractons”) that are strictly immobile at zero temperature\, and by degenerate ground-states that are locally indistinguishable.  Fracton excitations provide an alternative to Fermi or Bose statistics in three spatial dimensions\, and these states of matter are a gateway for exploring mechanisms for quantum information storage\, and for studying “slow” dynamical behavior in the absence of disorder. I will review exactly solvable models for these phases\, constructions of these states using well-studied two-dimensional topological phases\, and a model in which the fracton excitations carry a protected internal degeneracy\, which provides a natural generalization of non-Abelian anyons to three spatial dimensions.  I will then describe recent advances in categorizing these states of matter using finite-depth unitary transformations.\n\n\n10/15/2018\nEthan Lake\nTitle: A primer on higher symmetries \nAbstract: The notion of a higher symmetry\, namely a symmetry whose charged objects have a dimension greater than zero\, is proving to be very useful for organizing our understanding of gauge theories and topological phases of matter. Just like regular symmetries\, higher symmetries can be gauged\, spontaneously broken\, and can have anomalies. I will review these aspects of higher symmetries and motivate why beyond their conceptual utility\, they are often an indispensable tool for making statements about dualities and phase diagrams of theories with gauge fields.\n\n\n10/22/2018 \nRoom G02\nYin-Chen He\, Perimeter\nTitle: Emergent QED3 and QCD3 in condensed matter system \nAbstract: QED3-Chern-Simons and QCD3-Chern-Simons theories are interesting critical theories in the 2+1 dimension. These theories are described by gapless Dirac fermions interacting with dynamical gauge fields (U(1)\, SU(N)\, U(N)\, etc.) with a possible Chern-Simon term. These theories have fundamental importance as it will flow to the 3D conformal field theories and have interesting dualities in the infrared. Various of condensed matter system are described by these critical theories. I will introduce several examples including the Dirac spin liquid in the frustrated magnets (kagome\, triangular lattice)\, quantum phase transitions in the fractional quantum Hall systems and Kitaev materials.\n\n\n10/29/2018\nDominic Williamson\, Yale \nVideo\nTitle: Symmetry and topological order in tensor networks \nAbstract: I will present an overview of how topological states of matter with global symmetries can be described using tensor networks. First reviewing the classification of 1D symmetry-protected topological phases with matrix product states\, before moving on to the description of 2D symmetry-enriched topological phases with projected-entangled pair states.\n\n\n11/13/2018 \nTuesday \n3:00-4:30pm\nJason Alicea\, Caltech\nTitle: Time-crystalline topological superconductors\n\n\n11/19/2018\nX. G. Wen\, MIT \nVideo\nTitle: A classification of 3+1D topological orders \nAbstract: I will discuss a classification of 3+1D topological orders in terms of fusion 2 category. The 3+1D topological orders can be divided into two classes: the ones without emergent fermions and the ones with emergent fermions. The 3+1D topological orders with emergent fermions can be further divided into two classes: the ones without emergent Majorana zero mode and the ones with emergent Majorana zero mode. I will present pictures to understand those 3+1D topological orders.\n\n\n12/3/2018 \n*Room G02*\nClaudio Chamon\, Boston University\nTitle: Many-body scar states with topological properties in 1D\, 2D\, and 3D. \nAbstract: We construct (some) exact excited states of a class of non-integrable quantum many-body Hamiltonians in 1D\, 2D and 3D. These high energy many-body “scar” states have area law entanglement entropy\, and display properties usually associated to gapped ground states of symmetry protected topological phases or topologically ordered phases of matter\, including topological degeneracies.\n\n\n12/10/2018 \nRoom G02\nAnders Sandvik\, Boston University and Institute of Physics\, CAS\, Beijing\nTitle: Quantum Monte Carlo simulations of exotic states in 2D quantum magnets \nAbstract: Some exotic ground states of 2D quantum magnets can be accessed through sign-free quantum Monte Carlo simulations of certain “designer Hamiltonians”. I will discuss recent examples within the J-Q family of models\, where the standard Heisenberg exchange J on the square lattice is supplemented by multi-spin terms Q projecting correlated singlets\, such that dimer (columnar valence-bond) order is favored. In addition to a possible deconfined quantum critical point separating the Neel and dimer phases\, I will discuss recent work on a modified model where a rather strongly first-order transition between the Neel state and a plaquette-singlet-solid is associated with emergent O(4) symmetry up to length scales of at least 100 lattice spacings. This type of transition may be realized in SrCu2(BO3)2 under pressure. I will also discuss a random-singlet state obtained when randomness is introduced in a system with dimerized ground state. This type of state may be realized in some frustrated disordered quantum magnets.\n\n\n1/8/2019\nLukasz Fidkowski\, Univ. of Washington \nVideo\nTitle: Non-trivial quantum cellular automata in 3 dimensions \nAbstract: Motivated by studying the entanglement structure of certain symmetry protected topological phases\, we construct a non-trivial quantum cellular automaton in a Hilbert space for a 3d lattice of spin 1/2 degrees of freedom.  This is an operator which takes local operators to nearby local operators\, but is not locally generated. We discuss implications for the classification of SPT phases in equilibrium and Floquet settings.\n\n\n3/18/2019\nAri Turner\, Technion \nVideo\nTitle:  Trapping Excitations at Phantasmagoric Wave Vectors \nAbstract:  This talk will explain some properties of the fracton state devised by Jeongwan Haah. A fracton state has excitations that are extremely localized–it is impossible for them to move (unlike Anderson localization\, e.g.–Anderson localized excitations can move if there is an external field to provide energy). One can understand why in a simple way using “mod 2” Fourier analysis. I will explain this\, and also introduce “finite fields”\, which are the number systems one needs to define exponentials mod. 2.\n\n\n4/1/2019\nYi-Zhuang You (UCSD)\nTitle: Emergent Symmetry and Conserved Currents at Deconfined Quantum Critical Points \nAbstract: Noether’s theorem is one of the fundamental laws of physics\, relating continuous symmetries and conserved currents. Here we explore the role of Noether’s  theorem at the deconfined quantum critical point (DQCP)\, which is an exotic quantum phase transition beyond the Landau-Ginzburg-Wilson paradigm. It was expected that a larger continuous symmetry could emerge at the DQCP\, which\, if true\, should lead to conserved current at low energy. By identifying the emergent current fluctuation in the spin excitation spectrum\, we can quantitatively study the current-current correlation in large-scale quantum Monte Carlo simulations. Our results reveal the conservation of the emergent current\, as signified by the vanishing anomalous dimension of the current operator\, and hence provide supporting evidence for the emergent symmetry at the DQCP. We also extend our discussion of emergent conserved current to the recently proposed one-dimensional analog of DQCP and confirm the emergent O(2)xO(2) symmetry in that case. Finally\, I will briefly discuss the significance of our findings in a potential realization of DQCP in the Shastry-Sutherland lattice material SrCu2(BO3)2.\n\n\n4/8/2019\nAdam Nahum (Oxford)\nTitle: Emergent statistical mechanics of entanglement in random unitary circuits \nAbstract: I will talk about quantum-classical mappings for real-time observables in some simple many-body systems (random unitary circuits). Specifically I will discuss how (1) entanglement entropy growth and (2) two-point correlation functions in these systems can be related to partition functions for interacting random walks. If time permits I will mention a phase transition in the entanglement structure of a repeatedly measured quantum state.\n\n\n4/16/2019 \nLyman 425 \n1:30pm\nXie Chen (Calthech)\nTitle: Foliated Fracton Order \nAbstract: The quantum information study of quantum codes and quantum memory has led to the discovery of a new class of exactly solvable lattice models called the fracton models. The fracton models are similar to the better understood topological models in that they also support fractional excitations and have stable ground state degeneracy. But it is also clear that the fracton models exist beyond the realm of conventional topological order due to their extensive ground state degeneracy and the restricted motion of their fractional excitations. In this talk\, I will present a new framework\, which we call the “foliated fracton order”\, to capture the nontrivial nature of the order in a large class of fracton models. Such a framework not only clarifies the connection between various different models\, but also points to the direction of search for interesting new features.\n\n\n4/24/2019 \n10:30am\nMichael Freedman (Microsoft Station Q) \nVideo\nTitle: Quantum cellular automata in higher dimensions \nAbstract: I’ll discuss Joint work with Matt Hastings on local endomorphisms of the operator algebra. We found these have a cohomological invariant similar to that of an incompressible flow.\n\n\n4/26/2019 \n10:30am\nMaissam Barkeshli (University of Maryland) \nVideo\nTitle: Relative anomalies in (2+1)D symmetry enriched topological states \nAbstract: It has recently been understood that some patterns of symmetry fractionalization in topologically ordered phases of matter are anomalous\, in the sense that they can only occur at the surface of a higher dimensional symmetry-protected topological (SPT) state. In this talk I will explain some recent advances in our understanding of how to compute relative anomalies between different symmetry fractionalization classes in (2+1)D topological states. The theory applies to general types of symmetries\, including symmetries that permute anyon types and space-time reflection symmetries. This allows us to compute anomalies for more general types of space-time reflection symmetries than previously known methods.\n\n\n5/3/2019\nYuan-Ming Lu (Ohio State)\nTitle: Spontaneous symmetry breaking from anyon condensation \nAbstract: In the context of quantum spin liquids\, it is long known that the condensation of fractionalized excitations can inevitably break certain physical symmetries. For example\, condensing spinons will usually break spin rotation and time reversal symmetries. We generalize these phenomena to the context of a generic continuous quantum phase transition between symmetry enriched topological orders\, driven by anyon condensation. We provide two rules to determine whether a symmetry is enforced to break across an anyon condensation transition or not. Using a dimensional reduction scheme\, we establish a mapping between these symmetry-breaking anyon-condensation transitions in two spatial dimensions\, and deconfined quantum criticality in one spatial dimension.\n\n\n5/9/2019 \n10:30am\nMichael Zaletel (UC Berkeley)\nTitle: Three-partite entanglement in CFTs and chiral topological orders \nAbstract: While the entanglement entropy provides an essentially complete description of two-partite entanglement\, multi-partite entanglement is far richer\, with a concomitant zoo of possible measures. This talk will focus on applications of one such measure\, the “entanglement of purification\,” in many-body systems. I will first present a holographic prescription for calculating it which we can compare with numerical calculations. Interestingly\, we find that a 1+1D CFT on a ring contains a universal number of GHZ states for any tri-partition of the ring. Using this result I’ll conjecture a bulk entanglement diagnostic for 2+1D chiral orders\, and solicit the audience’s help in proving or disproving it.\n\n\n5/28/2019 \n10:30am\nMasaki Oshikawa (U Tokyo)\nTitle: Gauge invariance\, polarization\, and conductivity \n  \nAbstract: The large gauge transformation on a quantum many-body system under a periodic boundary condition has had numerous applications including generalizations of Lieb-Schultz-Mattis theorem. It is also deeply related to the electric polarization in insulators. I will discuss an application to a scaling of the fluctuation of the polarization in conductors\, and also to general constraints on the electric conductivity.\n\n\n7/18/2019\nEslam Khalaf (Harvard)\n\n\nTitle: Dynamical correlations in anomalous disordered wires \n\nAbstract: In a (multichannel) disordered wire\, classical diffusion at short times (large frequencies) gives way to Anderson localization at long times (small frequencies). I study what happens in a disordered wire with topologically protected channels\, e.g. a wire with unequal number of left and right movers which is realizable at the edge of a Quantum Hall system. In this case\, the classical dynamics are described by diffusion + drift\, but it is unclear what the effect of quantum corrections in the long time (small frequency) limit is.\n\nThe problem is described by a 0+1-dimensional supersymmetric (graded) non-linear sigma model with a topological WZW term and a scalar potential. The computation of the local dynamical correlations of this model is equivalent to finding the ground state (zero mode) of the Laplace-Beltrami operator on a symmetric superspace with specific scalar and vector potentials. Surprisingly\, I find that this zero mode has a relatively simple explicit integral representation in the Wigner-Dyson symmetry classes which has no counterpart in the absence of supersymmetry. This leads to an exact mapping between the local correlation functions in this 0+1D theory and observables in a 0+0D chiral random matrix problem.\n\nThe mapping is used to explicitly compute two simple dynamical observables: the diffusion probability of return and the correlation of local density of states. In the former\, we find that the interference effects change the exponential decay expected from drift-diffusion to a power law decay. In the latter\, we find that the local density of states exhibits statistical level attraction in contrast to the level repulsion expected in a a standard Anderson insulator. At the end\, I discuss possible relationship to the recently developed framework of non-Hermitian topological systems.
URL:https://live-hu-cmsa-222.pantheonsite.io/event/topological-aspects-of-condensed-matter-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180910T103000
DTEND;TZID=America/New_York:20180910T120000
DTSTAMP:20240213T103024Z
CREATED:20240213T103024Z
LAST-MODIFIED:20240213T103024Z
UID:10002433-1536575400-1536580800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:9/10/18 Topology Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/9-10-18-topology-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180924T175600
DTEND;TZID=America/New_York:20180924T175600
DTSTAMP:20240213T102402Z
CREATED:20240213T102402Z
LAST-MODIFIED:20240213T102402Z
UID:10002417-1537811760-1537811760@live-hu-cmsa-222.pantheonsite.io
SUMMARY:9/24/2018 Topological Aspects of Condensed Matter Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/9-24-2018-topological-aspects-of-condensed-matter-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181009T180500
DTEND;TZID=America/New_York:20181009T180500
DTSTAMP:20240213T104106Z
CREATED:20240213T104106Z
LAST-MODIFIED:20240213T104106Z
UID:10002451-1539108300-1539108300@live-hu-cmsa-222.pantheonsite.io
SUMMARY:10/09/2018 Topological Aspects of Condensed Matter Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/10-09-2018-topological-aspects-of-condensed-matter-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181015T181400
DTEND;TZID=America/New_York:20181015T181400
DTSTAMP:20240213T105335Z
CREATED:20240213T105335Z
LAST-MODIFIED:20240213T105335Z
UID:10002465-1539627240-1539627240@live-hu-cmsa-222.pantheonsite.io
SUMMARY:10/15/2018 Topology Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/10-15-2018-topology-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181019T110000
DTEND;TZID=America/New_York:20181019T230000
DTSTAMP:20240213T105229Z
CREATED:20240213T105229Z
LAST-MODIFIED:20240213T105229Z
UID:10002464-1539946800-1539990000@live-hu-cmsa-222.pantheonsite.io
SUMMARY:10/19/2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/10-19-2018-mirror-symmetry-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181022T100000
DTEND;TZID=America/New_York:20181022T113000
DTSTAMP:20240213T104846Z
CREATED:20240213T104846Z
LAST-MODIFIED:20240213T104846Z
UID:10002459-1540202400-1540207800@live-hu-cmsa-222.pantheonsite.io
SUMMARY:10/22/2018 Topology Seminar
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/10-22-2018-topology-seminar/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181026T182000
DTEND;TZID=America/New_York:20181026T182000
DTSTAMP:20240213T110858Z
CREATED:20240213T110858Z
LAST-MODIFIED:20240213T110858Z
UID:10002478-1540578000-1540578000@live-hu-cmsa-222.pantheonsite.io
SUMMARY:10/26/2018 Social Science Applications Forum
DESCRIPTION:
URL:https://live-hu-cmsa-222.pantheonsite.io/event/10-26-2018-social-science-applications-forum/
LOCATION:MA
CATEGORIES:Seminars
END:VEVENT
END:VCALENDAR