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X-ORIGINAL-URL:https://cmsa.fas.harvard.edu
X-WR-CALDESC:Events for CMSA
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DTSTART;TZID=America/New_York:20230202T123000
DTEND;TZID=America/New_York:20230202T133000
DTSTAMP:20240121T174936Z
CREATED:20230817T175011Z
LAST-MODIFIED:20240121T174936Z
UID:10001272-1675341000-1675344600@cmsa.fas.harvard.edu
SUMMARY:Neural Optimal Stopping Boundary
DESCRIPTION:Speaker: Max Reppen (Boston University) \nTitle: Neural Optimal Stopping Boundary \nAbstract:  A method based on deep artificial neural networks and empirical risk minimization is developed to calculate the boundary separating the stopping and continuation regions in optimal stopping. The algorithm parameterizes the stopping boundary as the graph of a function and introduces relaxed stopping rules based on fuzzy boundaries to facilitate efficient optimization. Several financial instruments\, some in high dimensions\, are analyzed through this method\, demonstrating its effectiveness. The existence of the stopping boundary is also proved under natural structural assumptions.
URL:https://cmsa.fas.harvard.edu/event/colloquium_2223/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/02CMSA-Colloquium-02.02.2023.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230207T120000
DTEND;TZID=America/New_York:20230207T130000
DTSTAMP:20240215T101240Z
CREATED:20230817T165237Z
LAST-MODIFIED:20240215T101240Z
UID:10001232-1675771200-1675774800@cmsa.fas.harvard.edu
SUMMARY:Motivic Geometry of Two-Loop Feynman Integrals
DESCRIPTION:Member Seminar \nSpeaker: Chuck Doran \nTitle: Motivic Geometry of Two-Loop Feynman Integrals \nAbstract: We study the geometry and Hodge theory of the cubic hypersurfaces attached to two-loop Feynman integrals for generic physical parameters. We show that the Hodge structure attached to planar two-loop Feynman graphs decomposes into a mixed Tate piece and a variation of Hodge structure from families of hyperelliptic curves\, elliptic curves\, or rational curves depending on the space-time dimension. We give more precise results for two-loop graphs with a small number of edges. In particular\, we recover a result of Spencer Bloch that in the well-known double box example there is an underlying family of elliptic curves\, and we give a concrete description of these elliptic curves. We show that the motive for the “non-planar” two-loop tardigrade graph is that of a family of K3 surfaces of generic Picard number 11. Lastly\, we show that generic members of the multi-scoop ice cream cone family of graph hypersurfaces correspond to pairs of multi-loop sunset Calabi-Yau varieties. Our geometric realization of these motives permits us in many cases to derive in full the homogeneous differential operators for the corresponding Feynman integrals. This is joint work with Andrew Harder and Pierre Vanhove.
URL:https://cmsa.fas.harvard.edu/event/member-seminar-2723/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230208T123000
DTEND;TZID=America/New_York:20230208T133000
DTSTAMP:20240214T112702Z
CREATED:20230817T175326Z
LAST-MODIFIED:20240214T112702Z
UID:10001273-1675859400-1675863000@cmsa.fas.harvard.edu
SUMMARY:From spin glasses to Boolean circuits lower bounds - Algorithmic barriers from the overlap gap property
DESCRIPTION:Speaker: David Gamarnik (MIT) \nTitle: From spin glasses to Boolean circuits lower bounds. Algorithmic barriers from the overlap gap property \nAbstract: Many decision and optimization problems over random structures exhibit an apparent gap between the existentially optimal values and algorithmically achievable values. Examples include the problem of finding a largest independent set in a random graph\, the problem of finding a near ground state in a spin glass model\, the problem of finding a satisfying assignment in a random constraint satisfaction problem\, and many many more. Unfortunately\, at the same time no formal computational hardness results exist which  explains this persistent algorithmic gap. \nIn the talk we will describe a new approach for establishing an algorithmic intractability for these problems called the overlap gap property. Originating in statistical physics theory of spin glasses\, this is a simple to describe property which a) emerges in most models known to exhibit an apparent algorithmic hardness; b) is consistent with the hardness/tractability phase transition for many models analyzed to the day; and\, importantly\, c) allows to mathematically rigorously rule out a large class of algorithms as potential contenders\, specifically the algorithms which exhibit a form of stability/noise insensitivity. \nWe will specifically show how to use this property to obtain stronger (stretched exponential) than the state of the art (quasi-polynomial) lower bounds on the size of constant depth Boolean circuits for solving the two of the aforementioned problems: the problem of finding a large independent set in a sparse random graph\, and the problem of finding a near ground state of a p-spin model. \nJoint work with Aukosh Jagannath and Alex Wein
URL:https://cmsa.fas.harvard.edu/event/collquium-2823/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/02CMSA-Colloquium-02.08.2023.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230213T123000
DTEND;TZID=America/New_York:20230213T133000
DTSTAMP:20240222T165748Z
CREATED:20230817T175704Z
LAST-MODIFIED:20240222T165748Z
UID:10001274-1676291400-1676295000@cmsa.fas.harvard.edu
SUMMARY:Complete Calabi-Yau metrics: Recent progress and open problems
DESCRIPTION:Speaker: Tristan Collins\, MIT \nTitle: Complete Calabi-Yau metrics: Recent progress and open problems \nAbstract: Complete Calabi-Yau metrics are fundamental objects in Kahler geometry arising as singularity models or “bubbles” in degenerations of compact Calabi-Yau manifolds.  The existence of these metrics and their relationship with algebraic geometry are the subjects of several long standing conjectures due to Yau and Tian-Yau. I will describe some recent progress towards the question of existence\, and explain some future directions\, highlighting connections with notions of algebro-geometric stability.
URL:https://cmsa.fas.harvard.edu/event/collquium-21323/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/02CMSA-Colloquium-02.13.2023-.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230214T120000
DTEND;TZID=America/New_York:20230214T130000
DTSTAMP:20240228T094059Z
CREATED:20230817T165432Z
LAST-MODIFIED:20240228T094059Z
UID:10001233-1676376000-1676379600@cmsa.fas.harvard.edu
SUMMARY:Dynamics of active nematic defects on cones
DESCRIPTION:Member Seminar \nSpeaker: Farzan Vafa \nTitle: Dynamics of active nematic defects on cones \nAbstract: In the first part of the talk\, we investigate the ground-state configurations of two-dimensional liquid crystals with p-fold rotational symmetry (p-atics) on cones. The cone apex develops an effective topological charge\, which in analogy to electrostatics\, leads to defect absorption and emission at the cone apex as the deficit angle of the cone is varied. We find three types of ground-state configurations as a function of cone angle\, which is determined by charged defects screening the effective apex charge: (i) for sharp cones\, all of the +1/p defects are absorbed by the apex; (ii) at intermediate cone angles\, some of the +1/p defects are absorbed by the apex and the rest lie equally spaced along a concentric ring on the flank; and (iii) for nearly flat cones\, all of the +1/p defects lie equally spaced along a concentric ring on the flank. We check these results with numerical simulations for a set of commensurate cone angles and find excellent agreement. In the second part of the talk\, we investigate the dynamics of an active nematic on a cone\, and via simulations find long-time circular orbits of either one or two flank defects\, with transitions between these states mediated by the apex via defect absorption\, emission\, or defect pair creation.
URL:https://cmsa.fas.harvard.edu/event/member-seminar-21423/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230221T120000
DTEND;TZID=America/New_York:20230221T130000
DTSTAMP:20240118T052804Z
CREATED:20230817T165641Z
LAST-MODIFIED:20240118T052804Z
UID:10001234-1676980800-1676984400@cmsa.fas.harvard.edu
SUMMARY:Hints of Flat Space Holography
DESCRIPTION:Member Seminar \nSpeaker: Dan Kapec \nTitle: Hints of Flat Space Holography \nAbstract: Despite our detailed understanding of holography in Anti-de Sitter space\, flat space holography remains somewhat mysterious. “Celestial CFT” is a formalism which attempts to recast quantum gravity in (d+2)-dimensional asymptotically flat spacetimes in terms of a d-dimensional Euclidean conformal field theory residing at the conformal boundary. I will discuss certain universal aspects of this correspondence. As in Anti-de Sitter space\, bulk gravitons produce a boundary stress tensor\, and bulk gluons furnish boundary-conserved currents. I will also show that continuous spaces of vacua in the bulk map directly onto the conformal manifold of the boundary CFT. This correspondence provides a new perspective on the role of the BMS group in flat space holography and offers a new interpretation of the antisymmetric double-soft gluon theorem in terms of the curvature of an infinite-dimensional vacuum manifold.
URL:https://cmsa.fas.harvard.edu/event/member-seminar-22123/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Member Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230222T123000
DTEND;TZID=America/New_York:20230222T133000
DTSTAMP:20240215T111058Z
CREATED:20230817T180053Z
LAST-MODIFIED:20240215T111058Z
UID:10001275-1677069000-1677072600@cmsa.fas.harvard.edu
SUMMARY:The Black Hole Information Paradox: A Resolution on the Horizon?
DESCRIPTION:Speaker: Netta Engelhardt (MIT) \nTitle: The Black Hole Information Paradox: A Resolution on the Horizon? \nAbstract: The black hole information paradox — whether information escapes an evaporating black hole or not — remains one of the most longstanding mysteries of theoretical physics. The apparent conflict between validity of semiclassical gravity at low energies and unitarity of quantum mechanics has long been expected to find its resolution in a complete quantum theory of gravity. Recent developments in the holographic dictionary\, and in particular its application to entanglement and complexity\, however\, have shown that a semiclassical analysis of gravitational physics can reproduce a hallmark feature of unitary evolution. I will describe this recent progress and discuss some promising indications of a full resolution of the information paradox.
URL:https://cmsa.fas.harvard.edu/event/collquium-22223/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/02CMSA-Colloquium-02.22.2023.png
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