Is a step in the primordial spectral index favored by CMB data ?

Details Is a step in the primordial spectral index favored by CMB data ? Is a step in the primordial spectral index favored by CMB data ?

2008-07-21

arxiv.org/abs/0807.3334v2

JCAP 0906:028,2009

Astronomy and Astrophysics

Astrophysics

Several new results, figures and enhanced discussion. Main conclusions unchanged. Matches the final version to be published in

Scientific paper

10.1088/1475-7516/2009/06/028

A sudden small change in the second derivative of the inflaton potential can result in a universal local feature in the spectrum of primordial perturbations generated during inflation. The exact solution describing this feature \cite{minu} is characterized by a step in the spectral index modulated by characteristic oscillations and results in a large running of the spectral index localized over a few e-folds of scale. In this paper we confront this step-like feature with the 5 year WMAP results and demonstrate that it provides a better fit to this data than a featureless initial spectrum. If such a feature exists at all, then it should lie at sufficiently large scales $k_0 \lesssim 0.003 {\rm Mpc}^{-1}$ corresponding to $l \lesssim 40$. The sign of the effect is shown to correspond to the negative running of $n_s$ localized near this scale. This feature could arise as a result of a `mini-waterfall'-type fast second order phase transition experienced by an auxiliary heavy field during inflation, in a model similar to hybrid inflation (though for a different choice of parameters). If this is the case, then the auxiliary field should be positively coupled to the inflaton.

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