Lagrangian approach of structure formation in Newtonian cosmologies with two fluids

Abstract

The Lagrangian approach of the structure formation is generalized to Newtonian cosmologies with two gravity-coupled fluids by applying the adhesion approximation to the multistreaming regime in the absence of thermodynamic pressures. The dynamic pressures arising from the velocity dispersion are considered as second-order terms. We obtain a semi-exact master evolution equation for the mixed fluid, and derive the evolution equation of each fluid by perturbation up to second order. We find that the effects of the relative motion of two fluids on the evolution of the fluid mixture are limited but will be comparatively significant at third and higher orders.