# Producing suprathermal tails in the stationary velocity distribution

## TL;DR

This paper explores mechanisms behind heavy tails in stationary velocity distributions across different systems, highlighting how localized dynamics and active diffusion lead to non-Maxwellian behaviors.

## Contribution

It introduces models combining localization, diffusive acceleration, and negative friction to explain suprathermal tails in velocity distributions.

## Key findings

- Kappa-distributions with power-law decay in space plasmas.
- Stretched exponential tails in vibrating granular gases.
- Velocity-dependent kinetic parameters cause non-Maxwellian distributions.

## Abstract

We revisit effective scenarios for the origin of heavy tails in stationary velocity distributions. A first analysis combines localization with diffusive acceleration. That gets realized in space plasmas to find the so-called kappa-distributions having power-law decay at high speeds. There, localization at high energy already takes place for the reversible dynamics but becomes effective by an active diffusion in velocity space. A model for vibrating granular gases and giving rise to stretched exponential tails is also briefly discussed, where negative friction is the energizer. In all cases, the resulting nonMaxwellian velocity distributions are frenetically caused by the dependence on the speed of kinetic parameters.