Poincar\'e Polynomials of Odd Diagram Classes

Abstract

An odd diagram class is a set of permutations with the same odd diagram. Brenti, Carnevale and Tenner showed that each odd diagram class is an interval in the Bruhat order. They conjectured that such intervals are rank-symmetric. In this paper, we present an algorithm to partition an odd diagram class in a uniform manner. As an application, we obtain that the Poincar\'e polynomial of an odd diagram class factors into polynomials of the form $1+t+\cdots+t^m$. This in particular resolves the conjecture of Brenti, Carnevale and Tenner.