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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190207T150000
DTEND;TZID=America/New_York:20190207T160000
DTSTAMP:20260517T064754
CREATED:20240212T112515Z
LAST-MODIFIED:20240212T112515Z
UID:10002074-1549551600-1549555200@cmsa.fas.harvard.edu
SUMMARY:2/7/2019 General Relativity Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/2-7-2019-general-relativity-seminar/
CATEGORIES:Colloquia & Seminar,Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190206T131000
DTEND;TZID=America/New_York:20190206T150000
DTSTAMP:20260517T064754
CREATED:20240212T111317Z
LAST-MODIFIED:20240212T111317Z
UID:10002046-1549458600-1549465200@cmsa.fas.harvard.edu
SUMMARY:2/6/2019 Hodge and Noether-Lefschetz Loci Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/2-6-2019-hodge-and-noether-lefschetz-loci-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190204T120000
DTEND;TZID=America/New_York:20190204T140000
DTSTAMP:20260517T064754
CREATED:20240212T111544Z
LAST-MODIFIED:20240212T111544Z
UID:10002051-1549281600-1549288800@cmsa.fas.harvard.edu
SUMMARY:2/4/2019 Math Physics Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/2-4-2019-math-physics-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190131T150000
DTEND;TZID=America/New_York:20190131T160000
DTSTAMP:20260517T064754
CREATED:20240212T095419Z
LAST-MODIFIED:20240212T095419Z
UID:10001941-1548946800-1548950400@cmsa.fas.harvard.edu
SUMMARY:1/31/2019 General Relativity Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-31-2019-general-relativity-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190130T133000
DTEND;TZID=America/New_York:20190130T150000
DTSTAMP:20260517T064754
CREATED:20240212T100318Z
LAST-MODIFIED:20240212T100318Z
UID:10001951-1548855000-1548860400@cmsa.fas.harvard.edu
SUMMARY:1/30/2019 Hodge and Noether-Lefschetz Loci Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-30-2019-hodge-and-noether-lefschetz-loci-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190128T000000
DTEND;TZID=America/New_York:20190128T000000
DTSTAMP:20260517T064754
CREATED:20240212T094919Z
LAST-MODIFIED:20240212T094919Z
UID:10001933-1548633600-1548633600@cmsa.fas.harvard.edu
SUMMARY:1/28/2018 Mathematical Physics Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-28-2018-mathematical-physics-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190126T000000
DTEND;TZID=America/New_York:20190127T130000
DTSTAMP:20260517T064754
CREATED:20240212T090434Z
LAST-MODIFIED:20240212T090434Z
UID:10001900-1548460800-1548594000@cmsa.fas.harvard.edu
SUMMARY:1/27/2020 Math Physics Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-27-2020-math-physics-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190123T133000
DTEND;TZID=America/New_York:20190123T150000
DTSTAMP:20260517T064754
CREATED:20240212T101950Z
LAST-MODIFIED:20240212T101950Z
UID:10001971-1548250200-1548255600@cmsa.fas.harvard.edu
SUMMARY:1/23/2019 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-23-2019-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190116T204600
DTEND;TZID=America/New_York:20190116T204600
DTSTAMP:20260517T064754
CREATED:20240213T110531Z
LAST-MODIFIED:20240213T110531Z
UID:10002474-1547671560-1547671560@cmsa.fas.harvard.edu
SUMMARY:1/16/2019 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-16-2019-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190108T140000
DTEND;TZID=America/New_York:20190108T140000
DTSTAMP:20260517T064754
CREATED:20240213T110236Z
LAST-MODIFIED:20240213T110236Z
UID:10002471-1546956000-1546956000@cmsa.fas.harvard.edu
SUMMARY:1/8/2019 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/1-8-2019-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181212T204300
DTEND;TZID=America/New_York:20181212T204300
DTSTAMP:20260517T064754
CREATED:20240213T110834Z
LAST-MODIFIED:20240213T110834Z
UID:10002476-1544647380-1544647380@cmsa.fas.harvard.edu
SUMMARY:12/12/2018 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/12-12-2018-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181210T204300
DTEND;TZID=America/New_York:20181210T204300
DTSTAMP:20260517T064754
CREATED:20240213T111028Z
LAST-MODIFIED:20240213T111028Z
UID:10002479-1544474580-1544474580@cmsa.fas.harvard.edu
SUMMARY:12/10/2018 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/12-10-2018-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181205T133000
DTEND;TZID=America/New_York:20181205T133000
DTSTAMP:20260517T064754
CREATED:20240213T111357Z
LAST-MODIFIED:20240213T111357Z
UID:10002483-1544016600-1544016600@cmsa.fas.harvard.edu
SUMMARY:12/5/2018 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/12-5-2018-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181203T100000
DTEND;TZID=America/New_York:20181203T113000
DTSTAMP:20260517T064754
CREATED:20240213T112258Z
LAST-MODIFIED:20240213T112258Z
UID:10002494-1543831200-1543836600@cmsa.fas.harvard.edu
SUMMARY:13/3/2018 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/13-3-2018-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181128T133000
DTEND;TZID=America/New_York:20181128T133000
DTSTAMP:20260517T064754
CREATED:20240213T100650Z
LAST-MODIFIED:20240213T100650Z
UID:10002392-1543411800-1543411800@cmsa.fas.harvard.edu
SUMMARY:11/28/2018 Hodge Lecture
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/11-28-2018-hodge-lecture/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181121T133000
DTEND;TZID=America/New_York:20181121T133000
DTSTAMP:20260517T064754
CREATED:20240213T101558Z
LAST-MODIFIED:20240213T101558Z
UID:10002408-1542807000-1542807000@cmsa.fas.harvard.edu
SUMMARY:11/21/2018 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/11-21-2018-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181114T133000
DTEND;TZID=America/New_York:20181114T133000
DTSTAMP:20260517T064754
CREATED:20240213T102050Z
LAST-MODIFIED:20240213T102050Z
UID:10002415-1542202200-1542202200@cmsa.fas.harvard.edu
SUMMARY:11/14/2018 Hodge Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/11-14-2018-hodge-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181107T150600
DTEND;TZID=America/New_York:20181107T150600
DTSTAMP:20260517T064754
CREATED:20240213T101931Z
LAST-MODIFIED:20240213T101931Z
UID:10002413-1541603160-1541603160@cmsa.fas.harvard.edu
SUMMARY:Hodge and Noether-Lefschetz Loci Seminar
DESCRIPTION:In the Fall 2018 Semester the CMSA will be hosting a seminar on Hodge and Noether-Lefschetz loci\, with lectures given by Hossein Movasati (IMPA). The seminar will occur weekly on Wednesday at 1:30 in room G10 of the CMSA. \n \nThe schedule below will be updated as talks are confirmed. \n\n\n\nDate\nTitle/Abstract\n\n\n11/7/2018 \nVideo\nTitle: Hodge and Noether-Lefschetz loci \nAbstract: Hodge cycles are topological cycles which are conjecturally (the millennium Hodge conjecture) supported in algebraic cycles of a given smooth projective complex manifold. Their study in families leads to the notion of Hodge locus\, which is also known as Noether-Lefschetz locus in the case of surfaces. The main aim of this mini course is to introduce a computational approach to the study of Hodge loci for hypersurfaces and near the Fermat hypersurface. This will ultimately lead to the verification of the variational Hodge conjecture for explicit examples of algebraic cycles inside hypersurfaces and also the verification of integral Hodge conjecture for examples of Fermat hypersurfaces. Both applications highly depend on computer calculations of rank of huge matrices. We also aim to review some classical results on this topic\, such as Cattani-Deligne-Kaplan theorem on the algebraicity of the components of the hodge loci\, Deligne’s absolute Hodge cycle theorem for abelian varieties etc. \nIn the theoretical side another aim is to use the available tools in algebraic geometry and construct the moduli space of projective varieties enhanced with elements in their algebraic de Rham cohomology ring. These kind of moduli spaces have been useful in mathematical physics in order to describe the generating function of higher genus Gromov-Witten invariants\, and it turns out that the Hodge loci in such moduli spaces are well-behaved\, for instance\, they are algebraic leaves of certain holomorphic foliations. Such foliations are constructed from the underlying Gauss-Manin connection. This lectures series involves many reading activities on related topics\, and contributions by participants are most welcome.\n\n\n11/14/2018 \nVideo\nTitle:  Integral Hodge conjecture for Fermat varieties \nAbstract: We describe an algorithm which verifies whether  linear algebraic cycles of the Fermat variety generate the lattice of Hodge cycles. A computer implementation of this  confirms the integral Hodge conjecture for quartic and quintic Fermat fourfolds. Our algorithm is based on computation of the list of elementary divisors of both the lattice of linear algebraic cycles\, and the lattice of Hodge cycles written in terms of  vanishing cycles\, and observing that these two lists are the same. This is a joint work with E. Aljovin and R. Villaflor.\n\n\n11/21/2018 \nVideo\nTitle:  Periods of algebraic cycles \nAbstract: The tangent space of the Hodge locus at a point can be described by the so called infinitesimal variation of Hodge structures and the cohomology class of Hodge cycles. For hypersurfaces of dimension $n$ and degree $d$ it turns out that one can describe it without any knowledge of cohomology theories and in a fashion which E. Picard in 1900’s wanted to study integrals/periods. The data of cohomology class is replaced with periods of Hodge cycles\, and explicit computations of these periods\, will give us a computer implementable description of the tangent space.  As an application of this we show that for examples of $n$ and $d$\, the locus of hypersurfaces containing two linear cycles whose intersection is of low dimension\, is a reduced component of the Hodge locus in the underlying parameter space.\n\n\n11/28/2018 \nVideo\nTitle: Periods of Complete Intersection Algebraic Cycles \nSpeaker: Roberto Villaflor \nAbstract: In order to compute periods of algebraic cycles inside even dimensional smooth degree d hypersurfaces of the projective space\, we restrict ourselves to cycles supported in a complete intersection subvariety. When the description of the complete intersection is explicit\, we can compute its periods\, and furthermore its cohomological class. As an application\, we can use this data to describe the Zariski tangent space of the corresponding Hodge locus\, as the degree d part of some Artinian Gorenstein ideal of the homogeneous coordinate ring of the projective space. Using this description\, we can show that for d>5\, the locus of hypersurfaces containing two linear cycles\, is a reduced component of the Hodge locus in the underlying parameter space.\n\n\n12/05/2018 \nRoom G02\nTitle: Some explicit Hodge cycles \nAbstract: Explicit examples of Hodge cycles are due to D. Mumford and A. Weil in the case of CM abelian varieties. In this talk\, I will describe few other examples for the Fermat variety. Effective verification of the Hodge conjecture for these cycles is not known.\n\n\n12/12/2018 \nVideo\nTitle: A conjectural Hodge locus for cubic tenfold \nAbstract: In this talk we will consider the difference  of two linear algebraic cycles of dimension 5 inside a smooth cubic tenfold and such that the dimension of their intersection is 3. We will show some computer assisted evidences to the fact that the corresponding Hodge locus is bigger than the expected locus of algebraic deformations of the cubic tenfold together with its linear cycles. A similar discussion will be also presented for cubic six and eightfold\,  for which we will prove that the corresponding second and third order infinitesimal Hodge loci are smooth. The main ingredient is a computer implementation of power series of periods of hypersurfaces.\n\n\n1/16/2019\nTitle: Algebraic BCOV anomaly equation \nAbstract: We introduce the moduli space T of  non-rigid compact Calabi-Yau threefolds enhanced with differential forms and a Lie algebra of vector fields in T. This will be used in order to give a purely algebraic interpretation of topological string partition functions and the Bershadsky-Cecotti-Ooguri-Vafa holomorphic anomaly equation (joint work with M. Alim\, E. Scheidegger\, S.-T. Yau).  We will also define similar moduli spaces for even dimensional Calabi-Yau varieties\, where we have the notion of Hodge locus.\n\n\n1/23/2019 \nVideo\nTitle: A new model for modular curves \nAbstract: One of the non-trivial examples of a Hodge locus is the modular curve X_0(N)\, which is due to isogeny of elliptic curves (a Hodge/algebraic cycle in the product of two elliptic curves). After introducing the notion of enhanced moduli of elliptic curves\, I will describe a new model for X_0(N) in the weighted projective space of dimension 4 and with weights (2\,3\,2\,3\,1). I will also introduce some elements in the defining ideal of such a model. \nThe talk is based on the article arXiv:1808.01689.\n\n\n1/30/2019 \nVideo\nTitle: Constant Yukawa couplings \nAbstract: In this talk I will first introduce algebraic Yukawa couplings for any moduli of enhanced Calabi-Yau n-folds. Then I will list many examples in support of the following conjecture. A moduli of Calabi-Yau n-folds is a quotient of a Hermitian symmetric domain (constructed from periods) by an arithmetic group if and only if the corresponding Yukawa couplings are constants.\n\n\n2/6/2019 \nVideo\nTitle: Integrality properties of CY modular forms \nAbstract: The integrality of the coefficients of the mirror map is a central problem in the arithmetic of Calabi-Yau varieties and it has been investigated  by Lian-Yau (1996\, 1998)\, Hosono-Lian-Yau (1996)\, Zudilin (2002)\, Kontsevich-Schwarz-Vologodsky (2006) Krattenthaler-Rivoal (2010). The central tool in most of these works has been the so called Dwork method.  In this talk we use this method and classify all hypergeometric differential equations with a maximal unipotent monodromy whose mirror map has integral coefficients. \nWe also  give a computable condition on the parameters of a hypergeometric function which conjecturally computes all the primes which appear in the denominators of the coefficients of the mirror map. This is a joint work with Kh. Shokri.\n\n\n2/13/2019\nTitle: Foliations and Hodge loci \nAbstract: In this talk I will introduce a holomorphic foliation in a larger parameter space attached to families of enhanced projective varieties. Irreducible components of the Hodge locus with constant periods are algebraic leaves of such a foliation. Under the hypothesis that these are all the algebraic leaves\,  we get the fact that such algebraic leaves are defined over the algebraic closure of the base field and that Hodge classes are weak absolute in the sense of C. Voisin.\n\n\n\n  \nReferences: \n\n\n\n\n\nM. Alim\, H. Movasati\, E. Scheidegger\, S.-T. Yau. Gauss-Manin connection in disguise: Calabi-Yau threefolds\, Comm. Math. Phys. 344\, (2016)\, no. 3\, 889-914.\nE. H. Cattani\, P. Deligne\, and A. G. Kaplan. On the locus of Hodge classes. Amer. Math. Soc.\, 8(2):483–506\, 1995.\nB. Haghighat H. Movasati\, S.-T. Yau. Calabi-Yau modular forms in limit: Elliptic fibrations\, Communications in Number Theory and Physics\, Vol. 11\, Number 4\, 879-912\, 2017.\nH. Movasati\, Modular and automorphic forms & beyond\, Book under preparation\, 2019.  \nH. Movasati. A Course in Hodge Theory: with Emphasis on Multiple Integrals.Book submitted\,2018.\nH. Movasati\, On elliptic modular foliation\, II\, 2018\nH. Movasati\, R. Villaflor Loyola\, Periods of linear algebraic cycles\,\, 2018. \nH. Movasati\, Gauss-Manin connection in disguise: Calabi-Yau modular forms\, Surveys in Modern Mathematics\, Vol 13\, International Press\, Boston.\nH. Movasati\, Gauss-Manin connection in disguise: Noether-Lefschetz and Hodge loci\, Asian Journal of Mathematics\, Vol.21\, No. 3\, pp. 463-482\, 2017. \nC. Voisin. Hodge loci and absolute Hodge classes. Compos. Math.\, 143(4):945–958\, 2007.\nC. Voisin. Hodge loci. Handbook of moduli. Vol. III\, volume 26 of Adv. Lect. Math. (ALM)}\, pages 507–546. Int. Press\, Somerville\, MA\, 2013.
URL:https://cmsa.fas.harvard.edu/event/hodge-and-noether-lefschetz-loci-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181029T103000
DTEND;TZID=America/New_York:20181029T103000
DTSTAMP:20260517T064754
CREATED:20240213T103526Z
LAST-MODIFIED:20240213T103526Z
UID:10002442-1540809000-1540809000@cmsa.fas.harvard.edu
SUMMARY:10/29/2018 Topological Aspects of Condensed Matter Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-29-2018-topological-aspects-of-condensed-matter-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181026T182000
DTEND;TZID=America/New_York:20181026T182000
DTSTAMP:20260517T064754
CREATED:20240213T110858Z
LAST-MODIFIED:20240213T110858Z
UID:10002478-1540578000-1540578000@cmsa.fas.harvard.edu
SUMMARY:10/26/2018 Social Science Applications Forum
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-26-2018-social-science-applications-forum/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181022T100000
DTEND;TZID=America/New_York:20181022T113000
DTSTAMP:20260517T064754
CREATED:20240213T104846Z
LAST-MODIFIED:20240213T104846Z
UID:10002459-1540202400-1540207800@cmsa.fas.harvard.edu
SUMMARY:10/22/2018 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-22-2018-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181019T110000
DTEND;TZID=America/New_York:20181019T230000
DTSTAMP:20260517T064754
CREATED:20240213T105229Z
LAST-MODIFIED:20240213T105229Z
UID:10002464-1539946800-1539990000@cmsa.fas.harvard.edu
SUMMARY:10/19/2018 Mirror Symmetry Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-19-2018-mirror-symmetry-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181015T181400
DTEND;TZID=America/New_York:20181015T181400
DTSTAMP:20260517T064754
CREATED:20240213T105335Z
LAST-MODIFIED:20240213T105335Z
UID:10002465-1539627240-1539627240@cmsa.fas.harvard.edu
SUMMARY:10/15/2018 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-15-2018-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181009T180500
DTEND;TZID=America/New_York:20181009T180500
DTSTAMP:20260517T064754
CREATED:20240213T104106Z
LAST-MODIFIED:20240213T104106Z
UID:10002451-1539108300-1539108300@cmsa.fas.harvard.edu
SUMMARY:10/09/2018 Topological Aspects of Condensed Matter Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/10-09-2018-topological-aspects-of-condensed-matter-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180924T175600
DTEND;TZID=America/New_York:20180924T175600
DTSTAMP:20260517T064754
CREATED:20240213T102402Z
LAST-MODIFIED:20240213T102402Z
UID:10002417-1537811760-1537811760@cmsa.fas.harvard.edu
SUMMARY:9/24/2018 Topological Aspects of Condensed Matter Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/9-24-2018-topological-aspects-of-condensed-matter-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180910T103000
DTEND;TZID=America/New_York:20180910T120000
DTSTAMP:20260517T064754
CREATED:20240213T103024Z
LAST-MODIFIED:20240213T103024Z
UID:10002433-1536575400-1536580800@cmsa.fas.harvard.edu
SUMMARY:9/10/18 Topology Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/9-10-18-topology-seminar/
CATEGORIES:Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180829T173600
DTEND;TZID=America/New_York:20180829T173600
DTSTAMP:20260517T064754
CREATED:20240213T102633Z
LAST-MODIFIED:20240213T102633Z
UID:10002424-1535564160-1535564160@cmsa.fas.harvard.edu
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://cmsa.fas.harvard.edu/event/topological-aspects-of-condensed-matter-seminar/
CATEGORIES:Seminars
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DTSTART;TZID=America/New_York:20180420T171800
DTEND;TZID=America/New_York:20180420T171800
DTSTAMP:20260517T064754
CREATED:20240213T101921Z
LAST-MODIFIED:20240213T101921Z
UID:10002412-1524244680-1524244680@cmsa.fas.harvard.edu
SUMMARY:4-20-2018 Social Science Applications Forum
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/4-20-2018-social-science-applications-forum/
CATEGORIES:Seminars
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180417T120000
DTEND;TZID=America/New_York:20180417T133000
DTSTAMP:20260517T064754
CREATED:20240213T100552Z
LAST-MODIFIED:20240213T100938Z
UID:10002389-1523966400-1523971800@cmsa.fas.harvard.edu
SUMMARY:4-17-2018 Special Algebraic Geometry Seminar
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/4-17-2018-special-algebraic-geometry-seminar/
CATEGORIES:Seminars
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180416T171600
DTEND;TZID=America/New_York:20180416T171600
DTSTAMP:20260517T064754
CREATED:20240213T101737Z
LAST-MODIFIED:20240213T101737Z
UID:10002409-1523898960-1523898960@cmsa.fas.harvard.edu
SUMMARY:4-16-2018 Social Science Applications Forum
DESCRIPTION:
URL:https://cmsa.fas.harvard.edu/event/4-16-2018-social-science-applications-forum/
CATEGORIES:Seminars
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