Prescribed Turán sign patterns for inverse Kazhdan-Lusztig polynomials of matroids

RESUMO

Gao and Xie conjectured that the coefficients of the ordinary, unnormalized inverse Kazhdan-Lusztig polynomial of every matroid are log-concave with no internal zeros. We give counterexamples and prove locality and composition formulas for deletions of projective charts. For every finite field and every nonempty finite set S contained in {2, 3, ...}, these formulas yield simple 3-connected matroids whose negative internal Turán determinants occur exactly at S. Their coefficients are positive and strictly decreasing. The polynomial degree can be prescribed above max S, and all selected Turán ratios can tend to zero simultaneously. The universal first-index inequality remains open.