# Mathematical Physics

This series consists of talks in the area of Mathematical Physics.

## Seminar Series Events/Videos

May 6 2019 - 2:00pm
Room #: 394
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May 13 2019 - 2:00pm
Room #: 394
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## Quantum geometry of moduli spaces of local systems

Monday Apr 22, 2019
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Let G be a split semi-simple algebraic group over Q. We introduce a natural cluster structure on moduli spaces of G-local systems over surfaces with marked points. As a consequence, the moduli spaces of G-local systems admit natural Poisson structures, and can be further quantized. We will study the principal series representations of such quantum spaces. It will recover many classical topics, such as the q-deformed Toda systems, quantum groups, as well as the modular functor conjecture for such representations, which should lead to new quantum invariants of threefolds.

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## Geometric quantisation on a hyper-Kähler vector space

Monday Apr 15, 2019
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In the context of geometric quantisation, one starts with the data of a symplectic manifold together with a pre-quantum line bundle, and obtains a quantum Hilbert space by means of the auxiliary structure of a polarisation, i.e. typically a Lagrangian foliation or a Kähler structure. One common and widely studied problem is that of quantising Hamiltonian flows which do not preserve it.

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## Mathematical hints of 3-d mirror symmetry

Monday Apr 15, 2019
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This is practice for a talk at Berkeley, so it will involve explaining stuff many people here probably already know.  I'll try to summarize what I've learned about 3 dimensional N=4 supersymmetric quantum field theories, their twists and how these manifest in terms of interesting objects in mathematics.  If nothing else, hopefully there will be some comedy value in my attempt.

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## Towards synthetic Euclidean quantum field theory

Monday Apr 08, 2019
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In a synthetic approach to geometry and physics, one attempts to formulate an axiomatic system in purely logical terms, abstracting away from irrelevant "implementation details". In this talk, I will explain how intuitionistic logic and topos theory provide a synthetic theory of space, and then consider a (naive version of) Euclidean QFTs in terms of a conjectural elegant synthetic reformulation: a Euclidean QFT is nothing but a probability space in intuitionistic logic, extended by suitable modalities formalizing compact regions of space.

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## Quantum Heisenberg categorification

Monday Mar 25, 2019
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The Heisenberg algebra plays a vital role in many areas of mathematics and physics.  We will describe a family of quantum Heisenberg categories, depending on a choice of central charge, that categorify this algebra.  When the central charge is nonzero, these categories act on modules for cyclotomic quotients of the affine Hecke algebra.  In central charge zero, we obtain an affinization of the HOMFLY-PT skein category, which acts on modules for $U_q(\mathfrak{gl}_n)$.  We will also discuss how the categories can be generalized by adding a Frobenius superalgebra into the construction.  This

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## Principal Bundles in Diophantine Geometry

Monday Mar 18, 2019
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Principal bundles and their moduli have been important in various aspects of physics and geometry for many decades. It is perhaps not so well-known that a substantial portion of the original motivation for studying them came from number theory, namely the study of Diophantine equations. I will describe a bit of this history and some recent developments.

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## Twisted 3d supersymmetric gauge theories and the enumerative geometry of quasi-maps

Monday Mar 18, 2019

I discuss a geometric interpretation of the twisted indexes of 3d (softly broken) $\cN=4$ gauge theories on $S^1 \times \Sigma$ where $\Sigma$ is a closed genus $g$ Riemann surface, mainly focussing on quivers with unitary gauge groups. The path integral localises to a moduli space of solutions to generalised vortex equations on $\Sigma$, which can be understood algebraically as quasi-maps to the Higgs branch. I demonstrate that the twisted indexes computed in previous work reproduce the virtual Euler characteristic of the moduli spaces of twisted quasi-maps.

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## Coulomb Phases and Anomalies: Geometric Approach to 5d/6d Theories

Wednesday Feb 20, 2019
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I will review the geometric approach to the description of Coulomb branches and Chern-Simons terms of gauge theories coming from compactifications of M-theory on elliptically fibered Calabi-Yau threefolds. Mathematically, this involves finding all the crepant resolutions of a given Weierstrass model and understanding the network of flops connecting them together with computing certain topological invariants. I will further check that the uplifted theory in 6d is anomaly-free using Green-Schwartz mechanism.

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## Continued Discussion

Monday Feb 11, 2019
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Continued discussion to the two informal talks given by Dylan Butson on January 21st and 28th.

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## Frobenius Heisenberg decategorification

Monday Feb 04, 2019
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The Heisenberg algebra plays an important role in many areas of mathematics and physics. Khovanov constructed a categorical analogue of this algebra which emphasizes its connections to representation theory and combinatorics. Recently, Brundan, Savage, and Webster have shown that the Grothendieck group of this category is isomorphic to the Heisenberg algebra. However, applying an alternative decategorification functor called the trace to the Heisenberg category yields a richer structure: a W-algebra, an infinite-dimensional Lie algebra related to conformal field theory.

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