Twisted equivariant quasi-elliptic cohomology and M-brane charge

In this paper we construct a twisted version of quasi-elliptic cohomology. This theory can be constructed as a K-theory of a loop space. After establishing basic properties of the theory, including restriction, change-of-group and induction maps, we construct the Chern character map. And we compute the twisted quasi-elliptic cohomology theories of representation 4-spheres acted by the finite subgroups of SU(2), which, as conjectured by Sati and Schreiber, can produce good observables on M-brane charge in a Tate-elliptic enhancement of D-brane charge in twisted equivariant K-theory.