Homological realization of the restricted Kostka polynomials

Abstract

In this paper we give two realizations of the restricted Kostka polynomials for $\sl_2$. Firstly we identify the restricted Kostka polynomials with a characters of the zero homology of the current algebra with a coefficients in a certain modules. As a corollary we reobtain the alternating sum formula. Secondly we show that the restricted Kostka polynomials are a $q$-multiplicities of the decomposition of the certain integrable $\hat{\sl}_2$-modules to the irreducible components. This allows to write a kind of fermionic formula for the Virasoro unitary models.