Hyatt's interlacing conjectures for half Eulerian polynomials

Let Bn{\mathfrak B}_n be the Coxeter group of type BB, realized as signed permutations, and let Dn{\mathfrak D}_n be its subgroup of even signed permutations. Define the half Eulerian polynomials Bn+(x)B_n^+(x) and Dn+(x)D_n^+(x) by summing xdesBσx^{\operatorname{des}_B\sigma} and xdesDσx^{\operatorname{des}_D\sigma}, respectively, over elements with positive final entry. For real-rooted polynomials, write g(x)f(x)g(x)\preceq f(x) when gg interlaces ff.

Hyatt's conjectures. For n1n\geq 1, Bn+(x)B_n^+(x) interlaces xnBn+(1/x)x^nB_n^+(1/x), and hence Bn(x)=Bn+(x)+xnBn+(1/x)B_n(x)=B_n^+(x)+x^nB_n^+(1/x) has only real zeros. For n2n\geq 2, Dn+(x)D_n^+(x) interlaces xnDn+(1/x)x^nD_n^+(1/x), and hence Dn(x)=Dn+(x)+xnDn+(1/x)D_n(x)=D_n^+(x)+x^nD_n^+(1/x) has only real zeros.

The source states that Hyatt confirmed these conjectures in a new version of the cited work, and the paper gives an affirmative answer by proving them.

Sources & referencesView supporting material

Primary source

Arthur L. B. Yang and Philip B. Zhang, “The Real-rootedness of Eulerian Polynomials via the Hermite–Biehler Theorem”, arXiv:1501.05824 (2015).

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