New Universal Local Feature in the Inflationary Perturbation Spectrum

TL;DR

This paper presents a model where a sudden change in the inflaton potential causes a localized running of the spectral index, potentially explaining WMAP observations of spectral index variation during inflation.

Contribution

It introduces a new inflationary scenario involving a rapid phase transition that modifies the perturbation spectrum, providing a possible explanation for observed spectral index running.

Findings

Density perturbation spectrum has a step in the spectral index.

Oscillations modulate the spectral index step.

Large running of the spectral index is localized over a few e-folds.

Abstract

A model is developed in which the inflaton potential experiences a sudden small change in its second derivative (the effective mass of the inflaton). An exact treatment demonstrates that the resulting density perturbation has a quasi-flat power spectrum with a break in its slope (a step in n_s). The step in the spectral index is modulated by characteristic oscillations and results in large running of the spectral index localised over a few e-folds of scales. A field-theoretic model giving rise to such behaviour of the inflationary potential is based on a fast phase transition experienced by a second scalar field weakly coupled to the inflaton. Such a transition is similar to that which terminates inflation in the hybrid inflationary scenario. This scenario suggests that the observed running of the spectral index in the WMAP data may be caused by a fast second order phase transition which occurred during inflation.