Heat equation for theta functions and vector-valued modular forms

Abstract

Abstract. We give a new method for constructing vector-valued modular forms from singular scalar-valued ones. As an application we prove the identity between two remarkable spaces of vector-valued modular forms which seem to be unrelated at a first look, since they are constructed in two very different ways. If V grad is the vector space generated by vector-valued modular forms constructed with gradients of odd theta functions and VΘ is the one generated by vector-valued modular forms arising from second order theta constants with our new construction, we will prove that V grad = VΘ.This result could also be proven as a consequence of the "heat equation" for theta functions.