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Algebraic Combinatorics· 2026Q1

Counting points on Hessenberg varieties over finite fields

Alex Abreu, Antonio Nigro, Samrith Ram

Short summary

A new formula counts points on arbitrary Hessenberg varieties over finite fields using modified Hall–Littlewood polynomials and the chromatic quasisymmetric function.

AI-generated from the title and abstract; the full text is not read.

Key points

  • A counting formula for points on Hessenberg varieties over finite fields is derived.
  • The formula utilizes modified Hall–Littlewood polynomials and the chromatic quasisymmetric function.
  • Poincaré polynomials of complex Hessenberg varieties are expressed using a Hall scalar product.
  • A new combinatorial proof for modified Hall–Littlewood polynomials is presented.

AI-generated from the title and abstract; the full text is not read.

Abstract

We give a counting formula in terms of modified Hall–Littlewood polynomials and the chromatic quasisymmetric function for the number of points on an arbitrary Hessenberg variety over a finite field. As a consequence, we express the Poincaré polynomials of complex Hessenberg varieties in terms of a Hall scalar product involving the symmetric functions above. We use these results to give a new proof of a combinatorial formula for the modified Hall–Littlewood polynomials.

The authors' abstract, as published at the source. Algebraic Combinatorics, 2026 · DOI ↗

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Field: Discrete Mathematics and Combinatorics

Discrete Mathematics and CombinatoricsMathematics