The theory of F-rational signature

TL;DR

This paper develops a comprehensive theory of F-rational signature, a numerical invariant in positive characteristic algebraic geometry, unifying and extending previous approaches to better detect F-rationality.

Contribution

It introduces a modified definition that aligns with Sannai's dual F-signature and advances the theory to fully generalize F-signature.

Findings

Unified theory of F-rational signature achieved

Modified definition agrees with Sannai's dual F-signature

Complete generalization of F-signature established

Abstract

F-signature is an important numeric invariant of singularities in positive characteristic that can be used to detect strong F-regularity. One would like to have a variant that rather detects F-rationality, and there are two theories that aim to fill this gap: F-rational signature of Hochster and Yao and dual F-signature of Sannai. Unfortunately, several important properties of the original F-signature are unknown for these invariants. We give a modification of the Hochster-Yao definition that agrees with Sannai's dual F-signature and push further the united theory to achieve a complete generalization of F-signature.