Sign sequences and decomposition numbers

Abstract

We obtain a closed formula for the $v$-decomposition numbers $d_{\lambda \mu }(v)$ arising from the canonical basis of the Fock space representation of $U_v({\widehat{\mathfrak{sl}}}_e)$, where the partition $\lambda$ is obtained from $\mu$ by moving some nodes in its Young diagram, all of which having the same $e$-residue. We also show that when these $v$-decomposition numbers are evaluated at $v=1$, we obtain the corresponding decomposition numbers for the Schur algebras and symmetric groups.