# Geometry of N=2 Supersymmetry 3 of 4

Date: Wed, Aug 25, 2021

Location: PIMS, University of Saskatchewan, Online, Zoom

Conference: 2nd PIMS Summer School on Algebraic Geometry in High Energy Physics

Subject: Mathematics, Algebraic Geometry, Physics, Particle Physics and Quantum Field Theory

Class: Scientific

### Abstract:

Coulomb branches of N=2 supersymmetric field theories in four dimensions support a rich geometry. My aim in these lectures will be to explain some aspects of this geometry, and its relation to the physics of the N=2 theories themselves.

I will first describe various constructions of N=2 theories and the corresponding Coulomb branches. In this story the main geometry visible is that of a complex integrable system, fibered over the Coulomb branch; one nice class of examples is associated to the Hitchin integrable system (moduli space of Higgs bundles over a Riemann surface). Fundamental objects in the N=2 theory (local operators, line operators, surface operators) all have geometric counterparts in the integrable system, as I will explain.

Next I will discuss a deformation of the story, which arises in physics from the Nekrasov-Shatashvili Omega-background. In this deformation, the Coulomb branch is replaced by a closely related space; for instance, the base of the Hitchin integrable system is replaced by a space parameterizing opers over the Riemann surface. One can use this deformation to give a concrete picture of the space of opers; in so doing one meets Stokes phenomena which are governed by the BPS indices (Donaldson-Thomas invariants) of the N=2 theory. This turns out to be closely related to the "exact WKB method" in analysis of ODEs. It is also connected to Riemann-Hilbert problems of a sort recently investigated by Bridgeland, as I will describe if time permits.