$C_2$-Equivariant Orthogonal Calculus (2501.14077v2)

Abstract: In this paper, we construct a version of orthogonal calculus for functors from $C_2$-representations to $C_2$-spaces, where $C_2$ is the cyclic group of order 2. For example, the functor $BO(-)$, that sends a $C_2$-representation to the classifying space of its orthogonal group, which has a $C_2$-action induced by the action on the $C_2$-representation. We obtain a bigraded sequence of approximations to such a functor, and via a zig-zag of Quillen equivalences, we prove that the homotopy fibres of maps between approximations are fully determined by orthogonal spectra with a genuine action of $C_2$ and a naive action of the orthogonal group $O(p,q):=O(\mathbb{R}^{p+q\delta})$.