Eulerian polynomials for multipermutations and signed multipermutations

In this paper, we study Eulerian polynomials for permutations and signed permutations of the multiset ${1,1,2,2,ldots,n,n}$. Properties of these polynomials, including recurrence relations and unimodality are discussed. In particular, we give a unified proof of the fact that these polynomials are unimodal with modes in the middle.