Primordial features due to a step in the inflaton potential

Abstract

Certain oscillatory features in the primordial scalar power spectrum are\nknown to provide a better fit to the outliers in the cosmic microwave\nbackground data near the multipole moments of $\\ell=22$ and 40. These features\nare usually generated by introducing a step in the popular, quadratic potential\ndescribing the canonical scalar field. Such a model will be ruled out, if the\ntensors remain undetected at a level corresponding to a tensor-to-scalar ratio\nof, say, $r\\simeq 0.1$. In this work, in addition to the popular quadratic\npotential, we investigate the effects of the step in a small field model and a\ntachyon model. With possible applications to future datasets (such as PLANCK)\nin mind, we evaluate the tensor power spectrum exactly, and include its\ncontribution in our analysis. We compare the models with the WMAP (five as well\nas seven-year), the QUaD and the ACBAR data. As expected, a step at a\nparticular location and of a suitable magnitude and width is found to improve\nthe fit to the outliers (near $\\ell=22$ and 40) in all these cases. We point\nout that, if the tensors prove to be small (say, $r\\lesssim 0.01$), the\nquadratic potential and the tachyon model will cease to be viable, and more\nattention will need to be paid to examples such as the small field models.\n