Role of Modified Chaplygin Gas in Accelerated Universe

Recent observations of the luminosity of type Ia supernovae indicate [1, 2] an accelerated expansion of the universe and lead to the search for a new type of matter which violate the strong energy condition ρ + 3p < 0. The matter consent responsible for such a condition to be satisfied at a certain stage of evolution of the universe is referred to as dark energy. There are different candidates to play the role of the dark energy. The type of dark energy represented by a scalar field is often called quintessence. The transition from a universe filled with matter to an exponentially expanding universe does not necessarily require the presence of the scalar field as the only alternative. In particular one can try another alternative by using an exotic type of fluid the so-called Chaplygin gas which obeys an equation of state like p = −B/ρ [3] where p and ρ are respectively the pressure and energy density and B is a positive constant. Subsequently the above equation was modified to the form p = −B/ρα with 0 ≤ α ≤ 1. This model gives the cosmological evolution from an initial dust like matter to an asymptotic cosmological constant with an epoch that can be seen as a mixture of a cosmological constant and a fluid obeying an equation of state p = αρ. This generalized model has been studied previously [4, 5].