BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//CMSA - ECPv6.15.20//NONSGML v1.0//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-ORIGINAL-URL:https://cmsa.fas.harvard.edu
X-WR-CALDESC:Events for CMSA
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-Robots-Tag:noindex
X-PUBLISHED-TTL:PT1H
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20200308T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20201101T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20210314T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20211107T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20220313T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20221106T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20230312T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20231105T060000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220125T090000
DTEND;TZID=America/New_York:20220125T100000
DTSTAMP:20260505T024601
CREATED:20240213T111559Z
LAST-MODIFIED:20240304T105047Z
UID:10002485-1643101200-1643104800@cmsa.fas.harvard.edu
SUMMARY:Adventures in Perturbation Theory
DESCRIPTION:Abstract: Recent years have seen tremendous advances in our understanding of perturbative quantum field theory—fueled largely by discoveries (and eventual explanations and exploitation) of shocking simplicity in the mathematical form of the predictions made for experiment. Among the most important frontiers in this progress is the understanding of loop amplitudes—their mathematical form\, underlying geometric structure\, and how best to manifest the physical properties of finite observables in general quantum field theories. This work is motivated in part by the desire to simplify the difficult work of doing Feynman integrals. I review some of the examples of this progress\, and describe some ongoing efforts to recast perturbation theory in terms that expose as much simplicity (and as much physics) as possible.
URL:https://cmsa.fas.harvard.edu/event/1-25-2022-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Combinatorics-Physics-and-Probability-Seminar-01.25.2022-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211214T093000
DTEND;TZID=America/New_York:20211214T103000
DTSTAMP:20260505T024601
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/
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:20211207T093000
DTEND;TZID=America/New_York:20211207T103000
DTSTAMP:20260505T024601
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/
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:20211130T093000
DTEND;TZID=America/New_York:20211130T103000
DTSTAMP:20260505T024601
CREATED:20240213T065738Z
LAST-MODIFIED:20240213T065738Z
UID:10002146-1638264600-1638268200@cmsa.fas.harvard.edu
SUMMARY:Resistance curvature – a new discrete curvature on graphs
DESCRIPTION:Abstract: The last few decades have seen a surge of interest in building towards a theory of discrete curvature that attempts to translate the key properties of curvature in differential geometry to the setting of discrete objects and spaces. In the case of graphs there have been several successful proposals\, for instance by Lin-Lu-Yau\, Forman and Ollivier\, that replicate important curvature theorems and have inspired applications in a variety of practical settings.\nIn this talk\, I will introduce a new notion of discrete curvature on graphs\, which we call the resistance curvature\, and discuss some of its basic properties. The resistance curvature is defined based on the concept of effective resistance which is a metric between the vertices of a graph and has many other properties such as a close relation to random spanning trees. The rich theory of these effective resistances allows to study the resistance curvature in great detail; I will for instance show that “Lin-Lu-Yau >= resistance >= Forman curvature” in a specific sense\, show strong evidence that the resistance curvature converges to zero in expectation for Euclidean random graphs\, and give a connectivity theorem for positively curved graphs. The resistance curvature also has a naturally associated discrete Ricci flow which is a gradient flow and has a closed-form solution in the case of vertex-transitive and path graphs.\nFinally\, if time permits I will draw a connection with the geometry of hyperacute simplices\, following the work of Miroslav Fiedler.\nThis work was done in collaboration with Renaud Lambiotte.
URL:https://cmsa.fas.harvard.edu/event/resistance-curvature-a-new-discrete-curvature-on-graphs/
CATEGORIES:Combinatorics Physics and Probability
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Combinatorics-Physics-and-Probability-Seminar-11.30.2021-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211123T093000
DTEND;TZID=America/New_York:20211123T103000
DTSTAMP:20260505T024601
CREATED:20240213T065330Z
LAST-MODIFIED:20240226T111143Z
UID:10002138-1637659800-1637663400@cmsa.fas.harvard.edu
SUMMARY:Prague dimension of random graphs
DESCRIPTION:Abstract: The Prague dimension of graphs was introduced by Nesetril\, Pultr and Rodl in the 1970s: as a combinatorial measure of complexity\, it is closely related to clique edges coverings and partitions. Proving a conjecture of Furedi and Kantor\, we show that the Prague dimension of the binomial random graph is typically of order n/(log n) for constant edge-probabilities. The main new proof ingredient is a Pippenger-Spencer type edge-coloring result for random hypergraphs with large uniformities\, i.e.\, edges of size O(log n).
URL:https://cmsa.fas.harvard.edu/event/11-23-21-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Combinatorics-Physics-and-Probability-Seminar-11.23.21-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211026T090000
DTEND;TZID=America/New_York:20211026T100000
DTSTAMP:20260505T024601
CREATED:20240213T113529Z
LAST-MODIFIED:20240304T101126Z
UID:10002507-1635238800-1635242400@cmsa.fas.harvard.edu
SUMMARY:The n-queens problem
DESCRIPTION:Abstract: The n-queens problem asks how many ways there are to place n queens on an n x n chessboard so that no two queens can attack one another\, and the toroidal n-queens problem asks the same question where the board is considered on the surface of a torus. Let Q(n) denote the number of n-queens configurations on the classical board and T(n) the number of toroidal n-queens configurations. The toroidal problem was first studied in 1918 by Pólya who showed that T(n)>0 if and only if n is not divisible by 2 or 3. Much more recently Luria showed that T(n) is at most ((1+o(1))ne^{-3})^n and conjectured equality when n is not divisible by 2 or 3. We prove this conjecture\, prior to which no non-trivial lower bounds were known to hold for all (sufficiently large) n not divisible by 2 or 3. We also show that Q(n) is at least ((1+o(1))ne^{-3})^n for all natural numbers n which was independently proved by Luria and Simkin and\, combined with our toroidal result\, completely settles a conjecture of Rivin\, Vardi and Zimmerman regarding both Q(n) and T(n). \nIn this talk we’ll discuss our methods used to prove these results. A crucial element of this is translating the problem to one of counting matchings in a 4-partite 4-uniform hypergraph. Our strategy combines a random greedy algorithm to count `almost’ configurations with a complex absorbing strategy that uses ideas from the methods of randomised algebraic construction and iterative absorption. \nThis is joint work with Peter Keevash.
URL:https://cmsa.fas.harvard.edu/event/10-26-2021-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211019T090000
DTEND;TZID=America/New_York:20211019T100000
DTSTAMP:20260505T024601
CREATED:20240213T114112Z
LAST-MODIFIED:20240304T100424Z
UID:10002511-1634634000-1634637600@cmsa.fas.harvard.edu
SUMMARY:10/19/2021 Combinatorics\, Physics and Probability Seminar
DESCRIPTION:Title: Ising model\, total positivity\, and criticality \nAbstract: The Ising model\, introduced in 1920\, is one of the most well-studied models in statistical mechanics. It is known to undergo a phase transition at critical temperature\, and has attracted considerable interest over the last two decades due to special properties of its scaling limit at criticality.\nThe totally nonnegative Grassmannian is a subset of the real Grassmannian introduced by Postnikov in 2006. It arises naturally in Lusztig’s theory of total positivity and canonical bases\, and is closely related to cluster algebras and scattering amplitudes.\nI will give some background on the above objects and then explain a precise relationship between the planar Ising model and the totally nonnegative Grassmannian\, obtained in our recent work with P. Pylyavskyy. Building on this connection\, I will give a new boundary correlation formula for the critical Ising model
URL:https://cmsa.fas.harvard.edu/event/10-19-2021-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211012T090000
DTEND;TZID=America/New_York:20211012T100000
DTSTAMP:20260505T024601
CREATED:20240213T114547Z
LAST-MODIFIED:20240304T100222Z
UID:10002513-1634029200-1634032800@cmsa.fas.harvard.edu
SUMMARY:10/12/2021 Combinatorics\, Physics and Probability Seminar
DESCRIPTION:Title: On counting algebraically defined graphs \nAbstract: For many classes of graphs that arise naturally in discrete geometry (for example intersection graphs of segments or disks in the plane)\, the edges of these graphs can be defined algebraically using the signs of a finite list of fixed polynomials. We investigate the number of n-vertex graphs in such an algebraically defined class of graphs. Warren’s theorem (a variant of a theorem of Milnor and Thom) implies upper bounds for the number of n-vertex graphs in such graph classes\, but all the previously known lower bounds were obtained from ad hoc constructions for very specific classes. We prove a general theorem giving a lower bound for this number (under some reasonable assumptions on the fixed list of polynomials)\, and this lower bound essentially matches the upper bound from Warren’s theorem.
URL:https://cmsa.fas.harvard.edu/event/10-12-2021-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211005T090000
DTEND;TZID=America/New_York:20211005T100000
DTSTAMP:20260505T024601
CREATED:20240213T113617Z
LAST-MODIFIED:20240304T085033Z
UID:10002508-1633424400-1633428000@cmsa.fas.harvard.edu
SUMMARY:10/5/2021 Combinatorics\, Physics and Probability Seminar
DESCRIPTION:Title: Geodesic Geometry on Graphs \nAbstract: In a graph G = (V\, E) we consider a system of paths S so that for every two vertices u\,v in V there is a unique uv path in S connecting them. The path system is said to be consistent if it is closed under taking subpaths\, i.e. if P is a path in S then any subpath of P is also in S. Every positive weight function w: E–>R^+ gives rise to a consistent path system in G by taking the paths in S to be geodesics w.r.t. w. In this case\, we say w induces S. We say a graph G is metrizable if every consistent path system in G is induced by some such w. \nWe’ll discuss the concept of graph metrizability\, and\, in particular\, we’ll see that while metrizability is a rare property\, there exists infinitely many 2-connected metrizable graphs. \nJoint work with Nati Linial.
URL:https://cmsa.fas.harvard.edu/event/10-5-2021-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210928T130000
DTEND;TZID=America/New_York:20210928T130000
DTSTAMP:20260505T024601
CREATED:20240214T045955Z
LAST-MODIFIED:20240304T060348Z
UID:10002535-1632834000-1632834000@cmsa.fas.harvard.edu
SUMMARY:9/28/2021 Combinatorics\, Physics and Probability Seminar
DESCRIPTION:Title: The hypersimplex and the m=2 amplituhedron \nAbstract: I’ll discuss a curious correspondence between the m=2 amplituhedron\, a 2k-dimensional subset of Gr(k\, k+2)\, and the hypersimplex\, an (n-1)-dimensional polytope in R^n. The amplituhedron and hypersimplex are both images of the totally nonnegative Grassmannian under some map (the amplituhedron map and the moment map\, respectively)\, but are different dimensions and live in very different ambient spaces. I’ll talk about joint work with Matteo Parisi and Lauren Williams in which we give a bijection between decompositions of the amplituhedron and decompositions of the hypersimplex (originally conjectured by Lukowski–Parisi–Williams). Along the way\, we prove the sign-flip description of the m=2 amplituhedron conjectured by Arkani-Hamed–Thomas–Trnka and give a new decomposition of the m=2 amplituhedron into Eulerian-number-many chambers (inspired by an analogous hypersimplex decomposition).
URL:https://cmsa.fas.harvard.edu/event/9-28-2021-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210921T093000
DTEND;TZID=America/New_York:20210921T093000
DTSTAMP:20260505T024601
CREATED:20240214T050308Z
LAST-MODIFIED:20240304T060511Z
UID:10002536-1632216600-1632216600@cmsa.fas.harvard.edu
SUMMARY:Surfacehedra and the Binary Positive Geometry of Particle and “String” Amplitudes
DESCRIPTION:Speaker: Nima Arkani-Hamed\, IAS \nTitle: Surfacehedra and the Binary Positive Geometry of Particle and “String” Amplitudes
URL:https://cmsa.fas.harvard.edu/event/9-21-2021-combinatorics-physics-and-probability-seminar/
LOCATION:Virtual
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210911T093000
DTEND;TZID=America/New_York:20210911T103000
DTSTAMP:20260505T024601
CREATED:20240222T111949Z
LAST-MODIFIED:20240222T112111Z
UID:10002807-1631352600-1631356200@cmsa.fas.harvard.edu
SUMMARY:Gradient flows on totally nonnegative flag varieties
DESCRIPTION:Abstract: One can view a partial flag variety in C^n as an adjoint orbit inside the Lie algebra of n x n skew-Hermitian matrices. We use the orbit context to study the totally nonnegative part of a partial flag variety from an algebraic\, geometric\, and dynamical perspective. We classify gradient flows on adjoint orbits in various metrics which are compatible with total positivity. As applications\, we show how the classical Toda flow fits into this framework\, and prove that a new family of amplituhedra are homeomorphic to closed balls. This is joint work with Anthony Bloch.
URL:https://cmsa.fas.harvard.edu/event/11-9-21-combinatorics-physics-and-probability-seminar/
CATEGORIES:Combinatorics Physics and Probability
END:VEVENT
END:VCALENDAR