Tachyon inflation : tests and comparison with single scalar field inflation

We compare the standard single scalar field inflationary predictions with those of an inflationary phase driven by a tachyon field. A slow-roll formalism is defined for tachyon inflation, and we derive the spectra of scalar and tensor perturbations as well as the consistency relations. At lowest order the predictions of standard and tachyon inflation are shown to be the same. Higher order deviations are present and their observational relevance is discussed. We then study some typical inflationary tachyon potentials, discuss their observational consequences and compare them with recent data. All the models predict a negative and very small running of the scalar spectral index, and they consistently lie within the 1σ contour of the data set. However, the regime of blue scalar spectral index and large gravity waves cannot be explored by these models. Finally, a new exact solution of the unperturbed and perturbed coupled gravity and tachyon equations is also presented.