title: Isometric fluctuation relations for equilibrium states with broken symmetry.
abstract: We derive a set of isometric fluctuation relations, which constrain the order parameter fluctuations in finite-size systems at equilibrium and in the presence of a broken symmetry. These relations are exact and should apply generally to many condensed-matter physics systems. Here, we establish these relations for magnetic systems and nematic liquid crystals in a symmetry-breaking external field, and we illustrate them on the Curie-Weiss and the XY models. Our relations also have implications for spontaneous symmetry breaking, which are discussed.
authors.affiliation: Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, PSL Research University, ESPCI, 10 rue Vauquelin, F-75231 Paris, France.
authors.forename: D
authors.initials: D
authors.lastname: Lacoste
authors.affiliation: Center for Nonlinear Phenomena and Complex Systems, Université Libre de Bruxelles, Code Postal 231, Campus Plaine, B-1050 Brussels, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Gaspard