# Positive Harris recurrence for degenerate diffusions with internal variables and randomly perturbed time-periodic input

## TL;DR

This paper establishes conditions under which a high-dimensional stochastic differential system with internal variables and periodic inputs is positive Harris recurrent, ensuring long-term stability and recurrence in biological and physical models.

## Contribution

It provides verifiable criteria linking deterministic dynamics and stochastic perturbations to guarantee positive Harris recurrence in complex systems.

## Key findings

- Conditions for recurrence are derived based on Lyapunov functions.
- Local Hörmander conditions are verified at attainable points.
- The results apply to models in biology and statistical mechanics.

## Abstract

We consider a multidimensional time-homogeneous dynamical system and add a randomly perturbed time-dependent deterministic signal to some of its components, giving rise to a high-dimensional system of stochastic differential equations, which is driven by possibly very low-dimensional noise. Equations of this type commonly occur in biology when modelling neurons or in statistical mechanics for certain Hamiltonian systems. We provide verifiable conditions on the original deterministic dynamical system under which the solution to the respective stochastic system features a point in the interior of its state space, which can be proved to be attainable by deterministic control arguments, and at which a local H\"ormander condition holds. Together with a Lyapunov condition, it follows that the corresponding process is positive Harris recurrent.