Evolution of matter perturbations and observational constraints on tachyon scalar field model

Abstract

Abstract In this paper, the tachyon scalar field model is compared with the Λ C D M standard model using a set of observational data consisting of BBN, H(z), CMB, BAO, SNIa and f ( z ) σ 8 . The comparison is carried out at background and perturbation levels. Since the mass of the tachyon scalar field is very small and its effective sound speed is in the order of the speed of light ( c e f f ≈ 1 ) , the dark energy component remains homogeneous. The tachyon scalar field of dark energy model depends on its potential, therefore we consider the tachyon scalar field model based on a potential which is very popular in the literature, here in this work V ( ϕ ) = n 4 π G ( 1 − 2 3 n ) 1 ∕ 2 ( ϕ − ϕ 0 ) − 2 is chosen as the potential for the tachyon scalar field model. The evolution of equation of state parameter, density parameter, dimensionless Hubble parameter, deceleration parameter, the linear growth factor, the growth rate and f ( z ) σ 8 ( z ) for the tachyon scalar field model is compared with the Λ C D M , the holographic and the new agegraphic DE models. Although the tachyon scalar field model guarantees the acceleration of the universe’s expansion, the evolution of the deceleration parameter of the tachyon scalar field model enters to accelerating phase earlier than the other models. The growth rate of the cosmic structures, f ( z ) , is non-negligible at low redshifts for the tachyon scalar field model. In order to put constraints on the free parameters of the tachyon scalar field model, a standard Markov Chain Monte Carlo (MCMC) minimization method is utilized based on recent expansion and growth observational data. According to the values of the Akaike and Bayesian information criteria, we show that the tachyon scalar field model is inconsistent with the observational data and we can omit the tachyon scalar field model with the considered potential in this paper. Despite the considered potential is very popular in the literature, we should search for a better potential according to the available observational data.