Stochastic continuum theory of active nematics

We derive a stochastic continuum theory of active nematics by direct coarse-graining of a generic microscopic model and study it numerically. This allows to clarify the microscopic origin of the various terms found and to determine the non-trivial structure of the noises. We show in particular that two terms coupling density and order the non-equilibrium active current argued before to be at the origin of giant density fluctuations, and a multiplicative conserved noise are necessary to obtain a faithful description of the original model.