The (anti-)holomorphic sector in $\mathbb{C}/Λ$-equivariant cohomology, and the Witten class

Abstract: Atiyah's classical work on circular symmetry and stationary phase shows how the $\hat{A}$-genus is obtained by formally applying the equivariant cohomology localization formula to the loop space of a simply connected spin manifold. The same technique, applied to a suitable ''antiholomorphic sector'' in the $\mathbb{C}/\Lambda$-equivariant cohomology of the conformal double loop space $\mathrm{Maps}(\mathbb{C}/\Lambda,X)$ of a rationally string manifold $X$ produces the Witten genus of $X$. This can be seen as an equivariant localization counterpart to Berwick-Evans supersymmetric localization derivation of the Witten genus.