Crossing the phantom divide line in universal extra dimensions

Abstract

We investigate the cosmic acceleration and the evolution of dark energy across the cosmological constant boundary in universal extra dimensions UED. We adopt an empirical approach to solve the higher-dimensional cosmological equations so that the deceleration parameter q is consistent with observations. The expressions for the jerk and deceleration parameters are independent of the number of dimensions n. The behavior of pressure in 4D shows a positive-to-negative transition corresponding to the deceleration-to-acceleration cosmic transition. This pressure behavior helps in providing an explanation to the cosmic deceleration-acceleration transition although the reason behind the transition itself remains unknown. In the conventional 4D cosmology, there is a no-go theorem prevents the EoS parameter of a single perfect fluid in FRW geometry to cross the ω=−1 boundary. The current model includes a single homogeneous but anisotropic perfect fluid in a homogeneous FRW metric with two different scale factors in the ordinary 4D and the UED. In contrast to the conventional 4D cosmology, we have found that the dark energy (DE) evolution in UED shows ω=−1 crossing. however, the no-go theorem is still respected in 4D where the EoS parameter doesn’t cross the ω=−1 boundary.