# Gavin Ball : Quadratic closed G2-structures

A closed G2-structure is a certain type of geometric structure on a 7-manifold M, given by a 'non-degenerate' closed 3-form. The local geometry of closed G2-structures is non-trivial, in contrast to the perhaps more familiar case of symplectic structures (where we instead have a non-degenerate closed 2-form). In particular, any closed G2-structure automatically induces a Riemannian metric on M. I will talk about a special class of closed G2-structures, those satisfying a further 'quadratic' condition. This is a second order PDE system first written down by Bryant that can be interpreted as a condition on the Ricci curvature of the induced metric. I will focus mainly on the case where the G2-structure is 'extremally Ricci-pinched', giving new examples and describing an unexpected relationship with maximal submanifolds in a certain negatively curved pseudo-Riemannian symmetric space.

**Category**: Geometry and Topology**Duration**: 01:34:38**Date**: October 1, 2018 at 3:10 PM**Views**: 155-
**Tags:**seminar, Geometry/topology Seminar

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