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

Understand

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 $l \lesssim 40$.