Dilogarithms, OPE and twisted T-duality

The lattice vertex operator algebra plays a central role in the quantization of the sigma model with target a flat torus. When this torus is twisted by a non-trivial gerbe or, in its T-dual side, if one studies non-trivial torus fibrations over tori, dilogarithmic singularities appear in the operator product expansions of fields. We will show how the classical identities of the dilogarithm function appear as factorizations of the corresponding correlation functions.