Mb. Halpern et N. Sochen, FLAT CONNECTIONS FOR CHARACTERS IN IRRATIONAL CONFORMAL FIELD-THEORY, International journal of modern physics A, 10(8), 1995, pp. 1181-1218
Following the paradigm on the sphere, we begin the study of irrational
conformal field theory (ICFT) on the torus. In particular, we find th
at the affine-Virasoro characters of ICFT satisfy heatlike differentia
l equations with fiat connections. As a first example, we solve the sy
stem for the general g/h coset construction, obtaining an integral rep
resentation for the general coset characters. In a second application,
we solve for the high-level characters of the general ICFT on simple
g, noting a simplification for the subspace of theories which possess
a nontrivial symmetry group. Finally, we give a geometric formulation
of the system in which the flat connections are generalized Laplacians
on the centrally extended loop group.