Nonlinear semigroups for delay equations in Hilbert spaces, inertial manifolds and dimension estimates

TL;DR

This paper develops elementary methods for constructing nonlinear semigroups for delay equations in Hilbert spaces, enabling analysis of their differentiability, inertial manifolds, and dimension estimates, with potential extensions to PDEs with delay.

Contribution

It introduces a less restrictive, more elementary approach to semigroup construction for delay equations, including differentiability and inertial manifold analysis.

Findings

Constructed solving operators and nonlinear semigroups for delay equations.

Analyzed differentiability properties of semigroups in Hilbert spaces.

Discussed dimension estimates and inertial manifolds for delay equations.

Abstract

We study the well-posedness of nonautonomous nonlinear delay equations in $\mathbb{R}^{n}$ as evolutionary equations in a proper Hilbert space. We present a construction of solving operators (nonautonomous case) or nonlinear semigroups (autonomous case) for a large class of such equations. The main idea can be easily extended for certain PDEs with delay. Our approach has lesser limitations and much more elementary than some previously known constructions of such semigroups and solving operators based on the theory of accretive operators. In the autonomous case we also study differentiability properties of these semigroups in order to apply various dimension estimates using the Hilbert space geometry. However, obtaining effective dimension estimates for delay equations is a nontrivial problem and we explain it by means of a scalar delay equation. We also discuss our adjacent results concerned with inertial manifolds and their construction for delay equations.