On the admissibility of unboundedness properties of forced deterministic and stochastic sublinear Volterra summation equations

TL;DR

This paper investigates the conditions under which unbounded solutions of perturbed sublinear Volterra summation equations exhibit specific unboundedness properties, establishing equivalences between solution and perturbation behaviors.

Contribution

It characterizes when solutions inherit unboundedness properties from perturbations in asymptotically sublinear Volterra equations, extending understanding of solution behavior.

Findings

Solution unboundedness mirrors perturbation unboundedness for properties U

Connections between maxima of solutions and forcing terms are established

Conditions for various unboundedness behaviors are identified

Abstract

In this paper we consider unbounded solutions of perturbed convolution Volterra summation equations. The equations studied are asymptotically sublinear, in the sense that the state--dependence in the summation is of smaller than linear order for large absolute values of the state. When the perturbation term is unbounded, it is elementary to show that solutions are also. The main results of the paper are mostly of the following form: the solution has an additional unboundedness property $U$ if and only if the perturbation has property $U$. Examples of property $U$ include monotone growth, monotone growth with fluctuation, fluctuation on $\mathbb{R}$ without growth, existence of time averages. We also study the connection between the times at which the perturbation and solution reach their running maximum, and the connection between the size of signed and unsigned running maxima of the solution and forcing term.