Power spectra in extended tachyon cosmologies

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 (Formula presented.) 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 (Formula presented.) is plotted for each case. The result is that the power spectrum of the standard tachyon field differs in many magnitude orders from the (Formula presented.)CDM. However, the one with(Formula presented.), 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 (Formula presented.) values for the tachionization (Formula presented.)CDM model and the fiducial model. The Statefinder parameters (Formula presented.), measuring the deviations of the analysed model from the concordance model, are also explicitly calculated. Our result suggest that, depending on the value of (Formula presented.), 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.