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

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For n≡0,1(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)=∑π∈Antdes(π)+1sides(π)+1,TSAn−(s,t)=∑π∈Sn∖Antdes(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 n≡0,1(mod4)n\equiv0,1\pmod4, then

TSAn±(s,t)=∑i,jγn,i,j±(st)i(s+t)j(1+st)n+1−2i−j,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 n≡0(mod2)n\equiv0\pmod2, then

TSBn±(s,t)=∑i,jγn,i,jB,±(st)i(s+t)j(1+st)n−2i−j,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)n−2i−j,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.

References

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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