Stability in Categories and Normal Projective Varieties over Perfect Fields

TL;DR

This paper introduces a new notion of stability in categories, linking it to Harder-Narasimhan sequences, and applies it to normal projective surfaces over perfect fields, establishing equivalences with Bridgeland stability and deriving classical inequalities.

Contribution

It develops a generalized stability framework in categories, connects it to existing stability notions, and applies it to normal projective surfaces over perfect fields, providing new proofs and results.

Findings

Existence of Δ-stability equivalent to HN sequences.

Equivalence of Δ-stability with Bridgeland stability on normal surfaces.

New effective restriction theorem for slope semistable sheaves.

Abstract

We present a notion of $\Delta$-stability and stability filtration in arbitrary categories which is equivalent to the existence of Harder-Narasimhan (HN) sequences on objects. Indeed it is equivalent to the existence of a zero morphism, a partial order on objects, and a collection of some universal sequences. In additive categories embedded in an ambient triangulated category, we could obtain a numerical polynomial or central charge of objects by calculating the Euler characteristic of slope sequences and objects, inducing a partial order and HN sequences. In the case of normal projective surfaces over an arbitrary perfect field $k$ we show the existence of $\Delta$-stabilities of degree one on the relevant bounded derived categories which is equivalent to the existence of Bridgeland's stabilities on normal surfaces. This result also leads to new effective restriction theorem of slope semistable sheave on normal projective varieties over perfect fields. Our approach also gives alternative proofs of Hodge Index Theorem and Bogomolov Inequality.