Some aspects of tachyon field cosmology

Abstract

We study inflation, perturbations, non-gaussinity and late-time cosmological dynamics of a tachyon field both minimally and non-minimally coupled to gravity. By analyzing the parameters space of the model, the viability of the model in confrontation with recent observational data is considered. In a dynamical system technique, we study the phase space dynamics of both minimally and non-minimally coupled tachyon field. We find the fixed points (lines in our setup) and explore their stability. Also, we perform a statefinder diagnostic to both cases and show that the trajectories of the state finder pairs reach a stable state which is corresponding to a ΛCDM scenario.PACS numbers: 98.80. Cq , 95.36.+x

Tachyon field inflation in light of BICEP2

“…As the figure shows, a tachyon field model with potentials such as a linear potential V ∼ θ [15], a quadratic potential V ∼ θ 2 , a potential as V ∼ θ 3 , a quartic potential V ∼ θ 4 , a potential motivated by axion monodromy, as V ∼ θ 2 3 [16] and an exponential potential V ∼ e −θ is totally outside the Planck+WMAP+BICEP2+BAO data. We note that a minimally coupled tachyon field inflation with potentials θ 2 and e −θ was supported by the Planck2013 data [7]. Now we see that a minimal tachyon model is ruled out by the Planck+WMAP+BICEP2+BAO joint data.…”

“…Once again, we see that a minimally coupled tachyon field inflation with mentioned potentials is not supported by this joint dataset. It should be noticed that, with an exponential potential the running of the scalar spectral index is far from the observational data and is not shown in the figure. A minimally coupled tachyon model with an intermediate potential (V = b θ −β with β = 4l−4 l−2 , where l is defined by a = a 0 exp(ϑt l ), 0 < l < 1) [7] is also quite outside the observational region and is not shown in figure 1.…”

“…For a tachyonic inflationary model the slow roll parameters, which are defined as ǫ = −Ḣ H 2 and η = − 1 HḦ H , take the following form [7] …”

“…In the presence of the nonminimal coupling and with the perturbed FRW metric (10), the scalar spectral index of the model is given by the following expression [7] …”

“…The simplest inflationary model is described by a scalar field which slowly rolls down its potential [1,2,3]. One of the scalar fields which can be responsible for the early time inflation in the history of the universe, is the tachyon field [4,5,6,7] described by the Dirac-Born-Infeld (DBI) action. There are a wide range of potentials corresponding to this field.…”