Low-l CMB Power Loss in String Inflation

TL;DR

This paper investigates how a fast roll phase at the start of inflation, modeled by string-inspired potentials, could explain the observed low power in the CMB at large scales, proposing a tunable potential modification.

Contribution

It introduces a steeper potential component in string-inspired inflation models to account for the low-l power suppression in the CMB.

Findings

String loop potentials are not steep enough to suppress large-scale power.

Adding a steeper potential component can produce the desired power suppression.

Proper tuning of the potential is necessary for the effect to match observations.

Abstract

The lack of power on large scales (l < 40) might have been observed by the PLANCK satellite. We argue that this putative feature can be explained by a phase of fast roll at the onset of inflation. We show that in the context of single field models what is required is an asymmetric inflection point model of which fibre inflation is a string motivated example. We study the ability of fibre inflation to generate a suppression of the CMB 2-point function power at low l, finding that the potential derived from string loops is not steep enough for this purpose. We introduce a steeper contribution to the potential, that dominates away from the inflationary region, and show that if properly tuned it can indeed lead to a spectrum with lack of power at large scales.