Third-order perturbative solutions in the Lagrangian perturbation theory   with pressure
  Lagrangian perturbation theory for cosmological fluid describes structure formation in the quasi-nonlinear stage well. We present a third-order perturbative equation for Lagrangian perturbation with pressure in both the longitudinal and transverse modes. Then we derive the perturbative solution for simplest case. 
Takayuki Tatekawa