# Mathematics Colloquia and Seminars

### Some instances of equivariant gamma-positivity in geometric combinatorics

Algebra & Discrete Mathematics

 Speaker: Christos Athanasiadis, University of Athens, Greece Related Webpage: http://users.uoa.gr/~caath/ Location: 1147 MSB Start time: Mon, Sep 30 2019, 12:10PM

Gamma-positivity provides a powerful method to prove
unimodality for polynomials with real symmetric coefficients. It
appeared in the seventies, in work of Foata and Sch"utzenberger
on the Eulerian polynomials, and attracted considerable attention
after work of Br"ande'n on poset Eulerian polynomials and Gal on
triangulations of spheres. Gamma-positivity admits a natural
equivariant generalization. This lecture will discuss some of
few known instances of equivariant gamma-positivity, related to
colored permutations and derangements on the enumerative side,
and to barycentric and edgewise subdivisions on the geometric
side. Somewhat surprisingly, the proofs involve group actions
on the homology of posets.