Fundamental temperature exclusively determines the validity of superstatistics
Constanza Farías, Sergio Davis
TL;DR
The paper addresses the range of validity of superstatistics by deriving necessary and sufficient conditions expressed solely in terms of the fundamental inverse temperature $β_F$ and its derivatives. It shows that a steady-state model is superstatistical if and only if $(-1)^n β_F^{(n)}(E;S)≥0$ for all $n≥0$, enabling explicit formulas for all moments and cumulants of the conditional distribution $P(β|E,S)$. The authors provide recurrence relations and a differential-equation framework to compute cumulants from $β_F$, and illustrate the theory with the $q$-canonical, Gaussian, and a simple correction to the canonical ensemble. This work clarifies the precise mathematical criteria for superstatistics and implies that noncanonical $β_F$ must be infinitely differentiable and non-polynomial, with direct implications for modeling nonequilibrium steady states in physics and beyond.
Abstract
The theory of superstatistics is a generalization of Boltzmann-Gibbs statistical mechanics which admits temperature fluctuations, and generates non-canonical ensembles from the distribution function of these fluctuations. Recently, some results have been presented showing that superstatistics is not universally applicable, but several conditions on the so-called fundamental inverse temperature function $β_F$ must be met by any superstatistical model. In this work we provide a set of neccessary and sufficient conditions for a non-equilibrium steady state model to be expressible by superstatistics, showing that $β_F$ by itself determines the existence of a superstatistical distribution of temperature.
