Gr\"obner methods for representations of combinatorial categories

TL;DR

This paper develops combinatorial criteria to analyze the algebraic properties of representations of combinatorial categories, including noetherianity and rationality of Hilbert series, unifying and strengthening previous results.

Contribution

It introduces general combinatorial conditions for Gr"obner bases and rationality in representations, providing unified proofs and extending results across various categories.

Findings

Established criteria for noetherianity of representations.

Proved rationality of Hilbert series using language theory.

Unified and strengthened proofs for known categories like FI-modules.

Abstract

Given a category C of a combinatorial nature, we study the following fundamental question: how does the combinatorial behavior of C affect the algebraic behavior of representations of C? We prove two general results. The first gives a combinatorial criterion for representations of C to admit a theory of Gr\"obner bases. From this, we obtain a criterion for noetherianity of representations. The second gives a combinatorial criterion for a general "rationality" result for Hilbert series of representations of C. This criterion connects to the theory of formal languages, and makes essential use of results on the generating functions of languages, such as the transfer-matrix method and the Chomsky-Sch\"utzenberger theorem. Our work is motivated by recent work in the literature on representations of various specific categories. Our general criteria recover many of the results on these categories that had been proved by ad hoc means, and often yield cleaner proofs and stronger statements. For example: we give a new, more robust, proof that FI-modules (originally introduced by Church-Ellenberg-Farb), and a family of natural generalizations, are noetherian; we give an easy proof of a generalization of the Lannes-Schwartz artinian conjecture from the study of generic representation theory of finite fields; we significantly improve the theory of $\Delta$-modules, introduced by Snowden in connection to syzygies of Segre embeddings; and we establish fundamental properties of twisted commutative algebras in positive characteristic.