Xie–Zhang's real-rootedness conjecture for normalized inverse Kazhdan–Lusztig polynomials

From papers

Let M\mathsf{M} be a matroid, and write its inverse Kazhdan–Lusztig polynomial as

QM(x)=q0+q1x++qsxs,Q_{\mathsf{M}}(x)=q_0+q_1x+\cdots+q_sx^s,

where s=degQMrk(M)12s=\deg Q_{\mathsf{M}}\leq\left\lfloor\frac{\operatorname{rk}(\mathsf{M})-1}{2}\right\rfloor. Define the normalization of QM(x)Q_{\mathsf{M}}(x) by

B(QM)(x)=(s0)q0+(s1)q1x++(ss)qsxs.\mathcal{B}(Q_{\mathsf{M}})(x)=\binom{s}{0}q_0+\binom{s}{1}q_1x+\cdots+\binom{s}{s}q_sx^s.

Xie–Zhang's conjecture. For every matroid M\mathsf{M}, the polynomial B(QM)(x)\mathcal{B}(Q_{\mathsf{M}})(x) is real-rooted.

This conjecture refines the log-concavity conjecture for the coefficients of QM(x)Q_{\mathsf{M}}(x) by applying binomial normalization and predicting the stronger property of real-rootedness. Its status is open in the supplied text.

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Sources & referencesView supporting material

Primary source

Tom Braden, Luis Ferroni, Jacob P. Matherne and Nutan Nepal, “Inverse Kazhdan-Lusztig polynomials of matroids under deletion”, arXiv:2510.01086 (2025).

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