Power spectra in extended tachyon cosmologies

TL;DR

This paper compares the power spectra of extended tachyon cosmologies with the standard $\\Lambda$CDM model, showing that certain tachyon models can mimic the concordance model's expansion but differ in perturbation behavior.

Contribution

It introduces a numerical analysis of perturbations in extended tachyon models, highlighting how different barotropic indexes affect the power spectrum and their potential to match observational data.

Findings

The power spectrum of standard tachyon fields differs significantly from $\\Lambda$CDM.

A specific tachyon model with $\\gamma_0=1.91$ closely matches the concordance model.

Statefinder parameters effectively distinguish between tachyon models and $\\Lambda$CDM.

Abstract

In the present work the power spectrum of a particular class of tachyon fields is compared with the one corresponding to a cosmological constant model. This is done for different barotropic indexes $\gamma_0$ and the background space time is assumed to be of the spatially flat Friedmann-Robertson-Walker type. The differential equation describing the perturbations is solved numerically and the power spectrum at the scale factor value $a=1$ is plotted for each case. The result is that the power spectrum of the standard tachyon field differs in many magnitude orders from the $\Lambda$CDM. However, the one with $\gamma_0=1.91$, which corresponds to a complementary tachyon field, coincides fairly well with the concordance model. Therefore, we conclude that the perturbed solutions constitute an effective method to distinguish between the different $\gamma_0$ values for the tachionization $\Lambda$CDM model and the fiducial model. The Statefinder parameters $\{r, s\}$, measuring the deviations of the analysed model from the concordance model, are also explicitly calculated. Our result suggest that, depending on the value of $\gamma_0$, these models can explain the observed expansion history or the perturbation power spectrum of the universe, but they may have problems in describing both features simultaneously.