Gamma-positivity conjectures for two-sided Eulerian polynomials of classical Weyl groups

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For n0,1(mod4)n\equiv 0,1\pmod 4, let An\mathcal{A}_n be the alternating subgroup of Sn\mathfrak{S}_n, and define

TSAn+(s,t)=πAntdes(π)+1sides(π)+1,TSAn(s,t)=πSnAntdes(π)+1sides(π)+1.\mathrm{TSA}_n^+(s,t)=\sum_{\pi\in\mathcal{A}_n}t^{\mathsf{des}(\pi)+1}s^{\mathsf{ides}(\pi)+1},\qquad \mathrm{TSA}_n^-(s,t)=\sum_{\pi\in\mathfrak{S}_n\setminus\mathcal{A}_n}t^{\mathsf{des}(\pi)+1}s^{\mathsf{ides}(\pi)+1}.

For even nn, define the type-BB polynomials TSBn+(s,t)\mathrm{TSB}_n^+(s,t) and TSBn(s,t)\mathrm{TSB}_n^-(s,t) by summing tdesB(π)sidesB(π)t^{\mathsf{des}_B(\pi)}s^{\mathsf{ides}_B(\pi)} over Bn+\mathfrak{B}_n^+ and Bn\mathfrak{B}_n^-. For positive nn, define the type-DD polynomials TSDn+(s,t)\mathrm{TSD}_n^+(s,t) and TSDn(s,t)\mathrm{TSD}_n^-(s,t) analogously over Dn+\mathfrak{D}_n^+ and Dn\mathfrak{D}_n^-. Gamma-positivity conjectures. (1) If n0,1(mod4)n\equiv0,1\pmod4, then

TSAn±(s,t)=i,jγn,i,j±(st)i(s+t)j(1+st)n+12ij,γn,i,j±0.\mathrm{TSA}_n^\pm(s,t)=\sum_{i,j}\gamma_{n,i,j}^\pm(st)^i(s+t)^j(1+st)^{n+1-2i-j},\qquad \gamma_{n,i,j}^\pm\geq0.

(2) If n0(mod2)n\equiv0\pmod2, then

TSBn±(s,t)=i,jγn,i,jB,±(st)i(s+t)j(1+st)n2ij,γn,i,jB,±0.\mathrm{TSB}_n^\pm(s,t)=\sum_{i,j}\gamma_{n,i,j}^{B,\pm}(st)^i(s+t)^j(1+st)^{n-2i-j},\qquad \gamma_{n,i,j}^{B,\pm}\geq0.

(3) For every positive integer nn,

TSDn±(s,t)=i,jγn,i,jD,±(st)i(s+t)j(1+st)n2ij,γn,i,jD,±0.\mathrm{TSD}_n^\pm(s,t)=\sum_{i,j}\gamma_{n,i,j}^{D,\pm}(st)^i(s+t)^j(1+st)^{n-2i-j},\qquad \gamma_{n,i,j}^{D,\pm}\geq0.

These conjectures extend gamma positivity from the two-sided Eulerian polynomial to positive and negative elements in types AA, BB, and DD. The supplied text gives no resolution status for them.

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Sources & referencesView supporting material

Primary source

Hiranya Kishore Dey and Sivaramakrishnan Sivasubramanian, “Gamma positivity of the Descent based Eulerian polynomial in positive elements of Classical Weyl Groups”, arXiv:1812.01927 (2018).

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