This entry records the article
on geometric models for elliptic cohomology with speculations about the formalization of 2-dimensional CFT as an extended (2-functorial) FQFT, motivated by the Witten genus.
In more recent developments the authors exchanged, for technical convenience, the conformal structure in favor of flat Riemannian structure in
(1,1)-dimensional Euclidean field theories and K-theory
(2,1)-dimensional Euclidean field theories and tmf