Unicellular LLT polynomials and twins of regular semisimple Hessenberg varieties

Abstract

Abstract The solution of Shareshian–Wachs conjecture by Brosnan–Chow linked together the cohomology of regular semisimple Hessenberg varieties and graded chromatic symmetric functions on unit interval graphs. On the other hand, it is known that unicellular LLT polynomials have similar properties to graded chromatic symmetric functions. In this paper, we link together the unicellular LLT polynomials and twin of regular semisimple Hessenberg varieties introduced by Ayzenberg–Buchstaber. We prove the palindromicity of LLT polynomials from topological viewpoint. We also show that modules of a symmetric group generated by faces of a permutohedron are related to a shifted unicellular LLT polynomial and observe the $e$-positivity of shifted unicellular LLT polynomials, which is established by Alexandersson–Sulzgruber in general, for path graphs and complete graphs through the cohomology of the twins.