Validity and Application of the Extended Lagrangian Perturbation Theory

Basing our discussion on the Lagrangian description of hydrodynamics, we studied the evolution of density uctuation for nonlinear cosmological dynamics. We solved hydrodynamic equations for a self-gravitating uid with pressure, given by a polytropic equation of state, using a perturbation method. In this conference, we discuss validity of these perturbative solutions and application for structure formation in the Universe. Especially we will notice the correspondence between past modi ed Lagrangian perturbation models and our model