Differential identities of finite dimensional algebras and polynomial growth of the codimensions

Let $A$ be a finite dimensional algebra over a field $F$ of characteristic zero. If $L$ is a Lie algebra acting on $A$ by derivations, then such an action determines an action of its universal enveloping algebra $U(L)$. In this case we say that $A$ is an algebra with derivation or an $L$-algebra. Here we study the differential $L$-identities of $A$ and the corresponding differential codimensions, $c_n^L (A)$, when $L$ is a finite dimensional semisimple Lie algebra. We give a complete characterization of the corresponding ideal of differential identities in case the sequence $c_n^L (A)$, $n=1,2,\dots$, is polynomially bounded. Along the way we determine up to PI-equivalence the only finite dimensional $L$-algebra of almost polynomial growth.