Effects Of Modified Chaplygin Gas As Dark Energy On Structure Formation In Universe By Using Spherical Collapse Theory

In recent years, the accurate observation data from SNe la, WMAP and SDSS indicate that the expansion of the universe is accelerating, which becomes one of the popular questions of the physics. But this result seem to conflict with the standard big bang cosmological model which is familar to us. In order to alleviate the contradiction, many theories have been proposed. There are two major kinds of mainline correction method:one is introducing new component of cosmic which is called dark energy with negative pressure, which is a homogeneous distribution in the big scale structure. The introduction of dark energy is actually a correction of the right of Einstein gravitational field equation. Alternative to it, we can consider modifying the part of geometry in the left of the Einstein’s equation.In this text,we will further investigate the effects of modified Chaplygin gas on the structure formation of universe in a flat universe. The background knowledge of modern cosmology is fist introduced, and we review the standard cosmology model then briefly give the summaries of the current established various dark energy model. Next we introduce the spherical collapse model and cluster cluster number counts in structure formation, which could combine the parameters of model with observation data, consequently distinguishing and estimating various dark energy models. So in the third part we specifically introduce the related research theory and method. In the following section, we select modified Chaplygin gas (MCG) model to specific application of the theory. After reviewing the relevant dynamic evolution of MCG, we discuss the influence of MCG as dark energy to structure formation with the spherical collapse model in non-linear regime, and divide the nonlinear process into two phases, the first process is from forming small density contrast to expanding until turnaround state. The second process is from turnaround state to virialation. We respectively discuss the density contrast of turnaround and virialation, and compare the results with GCG, LCDM, Einstein-de sitter. For the linear regime, we just choose some cosmology parameters to research, and make the contrast with the observation, the result consists well with observation. Therefor the model of modified Chaplygin gas as dark energy could explain the accelerating universe well in linear and non-linear perturbations. Finally we use Press-shceter mass function to calculate the evolution of the cluster abundance in different ranges of mass, and contrast the result with the standard LCDM model, GCG model and parameterized dark energy model.