Towards refined curve counting on the Enriques surface I: K-theoretic refinements

Abstract: We conjecture an explicit formula for the $K$-theoretically refined Vafa-Witten invariants of the Enriques surface. By a wall-crossing argument the conjecture is equivalent to a new conjectural formula for the K-theoretically refined Pandharipande-Thomas invariants of the local Enriques surface. Evidence for the conjecture is given in several cases. We also comment on the case of K3 surfaces previously studied by Thomas.