The orthogonal unit group of the trivial source ring

Abstract

Let G be a finite group, p a prime, and (K,O,F) a p-modular system. We prove that the trivial source ring of OG is isomorphic to the ring of coherent G-stable tuples (χP), where χP is a virtual character of K[NG(P)/P], P runs through all p-subgroups of G, and the coherence condition is the equality of certain character values. We use this result to describe the group of orthogonal units of the trivial source ring as the product of the unit group of the Burnside ring of the fusion system of G with the group of coherent G-stable tuples (φP) of homomorphisms NG(P)/P→F×. The orthogonal unit group of the trivial source ring of OG is of interest, since it embeds into the group of p-permutation autoequivalences of OG.