The Poincar\'e-extended ab-index

Motivated by a conjecture concerning Igusa local zeta functions for intersection posets of hyperplane arrangements, we introduce and study the Poincar\'e-extended ab-index, which generalizes both the ab-index and the Poincar\'e polynomial. For posets admitting R-labelings, we give a combinatorial description of the coefficients of the extended ab-index, proving their nonnegativity. In the case of intersection posets of hyperplane arrangements, we prove the above conjecture of the second author and Voll as well as another conjecture of the second author and K\"uhne. We also define the pullback ab-index generalizing the cd-index of face posets for oriented matroids. This recovers, generalizes and unifies results from Billera--Ehrenborg--Readdy, Bergeron--Mykytiuk--Sottile--van~Willigenburg, Saliola--Thomas, and Ehrenborg.