Hermitian Jacobi Forms Having Modules as their Index and Vector-Valued Jacobi Forms

Abstract

We develop the theory of Hermitian Jacobi forms of lattice index, for both definite and indefinite Hermitian lattices. We also prove a theta decomposition theorem for vector-valued Jacobi forms (both in the orthogonal and Hermitian settings), with enhanced periodicity properties. This allows us to give a good definition of orthogonal and Hermitian Jacobi forms of matrix index, when the matrix need not be integral in any natural sense.