The calculus of thermodynamical formalism

TL;DR

This paper investigates the geometric and analytical properties of the space of normalized potentials and the Gibbs map in thermodynamical formalism, providing new insights into their structure and dynamics.

Contribution

It proves that the set of normalized potentials forms an analytic submanifold, computes the derivative of the Gibbs map, and introduces a natural weak Riemannian metric for analyzing gradient flows.

Findings

Normalized potentials form an analytic submanifold

Computed the derivative of the Gibbs map

Introduced a weak Riemannian metric and analyzed gradient flows

Abstract

Given a finite-to-one map acting on a compact metric space, one classically constructs for each potential in an appropriate Banach space of functionsa transfer operator acting on functions. Under suitable condition, the Ruelle-Perron-Frobenius enable to define for each potential an invariant measure called the Gibbs measure. The set of potential giving birth to the same Gibbs measure is a linear subspace containing one distinguished potential, said to be normalized.The goal of the present article is to study the geometry of the set of normalized potentials, of the normalization map, and of the Gibbs map sending potentials to Gibbs measures. We give an easy proof of the fact that the set of normalized potentials is an analytic submanifold and that the normalization map is analytic; we compute the derivative of the Gibbs map; last we endow the set of normalized potential with a natural weakRiemannian metric (derived from the asymptotic variance) with respect to which we compute the gradient flow induced by the pressure with respect to a given potential, e.g. the metric entropy functional.We also apply these ideas to recover in a wide setting existence and uniqueness of equilibrium states, possibly under constraints.