Rankin--Cohen Type Differential Operators on Hermitian Modular Forms

Abstract

We construct Rankin-Cohen type differential operators on Hermitian modular forms of signature $(n,n)$. The bilinear differential operators given here specialize to the original Rankin-Cohen operators in the case $n=1$, and more generally satisfy some analogous properties, including uniqueness. Our approach builds on previous work by Eholzer-Ibukiyama in the case of Siegel modular forms, together with results of Kashiwara-Vergne on the representation theory of unitary groups.