Spectrum and convergence of eventually positive operator semigroups

TL;DR

This paper extends spectral and convergence results known for positive semigroups to the broader class of eventually positive semigroups, which are relevant in differential equations, by developing new spectral characterizations and a version of the Niiro-Sawashima theorem.

Contribution

It generalizes convergence and spectral theorems from positive to eventually positive semigroups, introducing novel proofs and a new spectral characterization.

Findings

Convergence theorems for eventually positive semigroups established.

A version of the Niiro-Sawashima theorem for eventually positive operators proved.

Spectral conditions characterizing long-term behavior of these semigroups.

Abstract

An intriguing feature of positive $C_0$-semigroups on function spaces (or more generally on Banach lattices) is that their long-time behaviour is much easier to describe than it is for general semigroups. In particular, the convergence of semigroup operators (strongly or in the operator norm) as time tends to infinity can be characterized by a set of simple spectral and compactness conditions. In the present paper, we show that similar theorems remain true for the larger class of (uniformly) eventually positive semigroups - which recently arose in the study of various concrete differential equations. A major step in one of our characterizations is to show a version of the famous Niiro-Sawashima theorem for eventually positive operators. Several proofs for positive operators and semigroups do not work in our setting any longer, necessitating different arguments and giving our approach a distinct flavour.