Unified dark fluid in Brans–Dicke theory

Sunil K Tripathy,Bivudutta Mishra,Dipanjali Behera

doi:10.1140/epjc/s10052-015-3371-3

Abstract

Anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans-Dicke theory with a self interacting potential. Wet dark fluid characterized by a linear equation of state is considered as the source of dark energy. Shear scalar is considered to be proportional to the expansion scalar simulating an anisotropic relationship among the directional expansion rates. The dynamics of the universe in presence of wet dark fluid in anisotropic background have been discussed. The presence of evolving scalar field makes it possible to get accelerating phase of expansion even for a linear relationship among the directional Hubble rates. It is found that, the anisotropy in expansion rates does not affect the scalar field, self interacting potential but it controls the non-evolving part of the Brans- Dicke parameter.

Highlights

Recent observations from distant type Ia supernovae (SNIa) suggest that currently the universe is undergoing a state of acceleration [1,2,3,4,5]. This intriguing discovery has led to the idea of an exotic form of energy, dubbed dark energy, that is responsible for the possible cosmic acceleration at late times
The presence of dark energy with a negative pressure is confirmed with additional evidence from observations of X-ray clusters [8], Baryon Acoustic Oscillations (BAO) [9], weak lensing [10] and integrated Sache–Wolfe effect [11,12]
Further it leads to the coincidence problem: why are we accelerating in the current epoch that the vacuum and dust energy density are of the same order? a good number of alternative candidates have been proposed in recent times

Summary

Introduction

Recent observations from distant type Ia supernovae (SNIa) suggest that currently the universe is undergoing a state of acceleration [1,2,3,4,5]. A simple candidate for dark energy can be a cosmological constant in the classical FRW model with an equation of state equal to −1. The fine tuning problem is concerned with the theoretically predicted value of the cosmological constant from quantum field theory which is larger than the observed value by an order of 10123 Further it leads to the coincidence problem: why are we accelerating in the current epoch that the vacuum and dust energy density are of the same order? Recent Planck data shows that the primordial power spectrum of curvature perturbation is slightly redshifted from the exact scale invariance [15] It is obvious from the Planck data that despite the notable success of CDM model at high multipoles, it does not provide a good fit to the temperature power spectrum at low multipoles [15].

Basic Equations

Unified dark fluid

Exponential model

H02 we get the

Power law model

Conclusion