Representation rings for fusion systems and dimension functions

We define the representation ring of a saturated fusion system $\mathcal{F}$ as the Grothendieck ring of the semiring of $\mathcal{F}$-stable representations, and study the dimension functions of $\mathcal{F}$-stable representations using the transfer map induced by the characteristic idempotent of $\mathcal{F}$. We find a list of conditions for an $\mathcal{F}$-stable super class function to be realized as the dimension function of an $\mathcal F$-stable virtual representation. We also give an application of our results to constructions of finite group actions on homotopy spheres.