We describe the construction of vector valued modular forms transforming under a given congruence representation of the modular group SL(2,Z) in terms of theta series. We apply this general setup to obtain closed and easily computable formulas for conformal characters of rational models of W-algebras. 2 Université Bordeaux I, UFR de Mathématiques et Informatiques, 351 rue de la Libération, 3340...

We consider a class of pseudodifferential operators, with crossed vector valued symbols, defined on the product of two closed manifolds. We study the asymptotic expansion of the counting function of positive selfadjoint operators in this class. Using a general Theorem of J. Aramaki, we can determine the first term of the asymptotic expansion of the counting function and, in a special case, we a...