phantom energy

We examine cosmological models with generalized phantom energy (GPE). Generalized phantom energy satisfies the supernegative equation of state, but its evolution with the scale factor is generally independent, i.e. not determined by its equation of state. The requirement of general covariance makes the gravitational constant time-dependent. It is found that a large class of distinct GPE models with different evolution of generalized phantom energy density and gravitational constant, but the same equation of state of GPE have the same evolution of the scale factor of the universe in the distant future. The time dependence of the equation of state parameter determines whether the universe will end in a de Sitter-like phase or diverge in finite time with the accompanying " Big Rip " effect on the bound structures. Results of recent cosmological observations, such as distant supernovae of type Ia (SNIa) [1] and cosmic microwave background radiation (CMBR) [2], have dramatically altered our perception of the dynamics and composition of the universe and reshaped the landscape of standard cosmology [3]. The universe seems to be in the phase of accelerated expansion, which started at a relatively small redshift, z ∼ 1. This acceleration is attributed to a new form of matter, usually referred to as dark energy, the nature of which is still not definitely established. Observations