Eur. Phys. J. E (2008) 27: 149-160
https://doi.org/10.1140/epje/i2008-10364-9

Regular Article

Thermal and non-thermal fluctuations in active polar gels

¹ Theoretical Condensed Matter Physics Division and Centre for Advanced Research and Education, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, 700 064, Kolkata (Calcutta), India
² Physicochimie Curie (CNRS-UMR168), Institut Curie, Section de Recherche, 26 rue d’Ulm, 75248, Paris Cedex 05, France
³ Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzerstr. 38, 01187, Dresden, Germany
⁴ ESPCI, 10 rue Vauquelin, 75231, Paris Cedex 05, France

^* e-mail: jean-francois.joanny@curie.fr

Received: 10 March 2008
Accepted: 28 July 2008
Published online: 11 September 2008

Abstract

We discuss general features of noise and fluctuations in active polar gels close to and away from equilibrium. We use the single-component hydrodynamic theory of active polar gels built by Kruse and coworkers to describe the cytoskeleton in cells. Close to equilibrium, we calculate the response function of the gel to external fields and introduce Langevin forces in the constitutive equations with correlation functions respecting the fluctuation-dissipation theorem. We then discuss the breakage of the fluctuation-dissipation theorem due to an external field such as the activity of the motors. Active gels away from equilibrium are considered at the scaling level. As an example of application of the theory, we calculate the density correlation function (the dynamic structure factor) of a compressible active polar gel and discuss possible instabilities.