Fusion systems are a generalisation of finite groups designed in a way to capture local structure at a prime motivated by the existence of "exotic" fusion systems; local structures that do not appear in any finite group. In this talk I will give a brief introduction to fusion systems with emphasis on how they relate to groups. I will then discuss recent work done on fusion invariant character theory, concluding with a short excursion into biset functor theory to state a character value formula for "induction" between fusion systems and a Frobenius reciprocity analogue.

A (saturated) fusion system on a p-group P contains data about conjugacy within P, the typical case being the system induced by a group on its Sylow p-subgroup. Fusion systems are completely determined by looking at their essential subgroups, which must admit an automorphism of order coprime to p. For p=2, we describe two new methods that address the question: given an essential subgroup $E<P$ of a fusion system on P, what can we say about P? In particular, one method gives us sufficient conditions to deduce that $E\triangleleft P$, while the other explores cases where we have strong control over the normaliser tower of E in P.

• as holomorphic functions on certain symplectic spaces
• as matrix coefficients of the Heisenberg (and metaplectic) representation,
• as sections of line bundles on abelian varieties.