New model of axion monodromy inflation and its cosmological implications

TL;DR

This paper introduces a novel axion monodromy inflation model derived from torsional cycles in type IIB string theory, predicting distinctive features in the CMB power spectrum and providing a potential explanation for observed anomalies.

Contribution

It presents a new realization of axion monodromy inflation with a step-like potential profile and analyzes its cosmological implications, including effects on primordial perturbations and CMB observations.

Findings

Boost in B-mode polarization at large scales.

Suppressed scalar perturbations near the critical scale.

Potential explanation for low-$\\ell$ CMB temperature anisotropy suppression.

Abstract

We propose a new realization of axion monodromy inflation in which axion monodromy arises from torsional cycles in a type IIB compactification. A class of monomial potentials is obtained with specific values for the power index. Moreover, the inflaton mass changes profile due to the couplings between various fields after compactification. Consequently, the potential obtains a step-like profile at some critical scale. We study the cosmological implications of one concrete realization of this model. At the background level, it realizes a sufficiently long inflationary stage, which allows for the violation of the slow-roll conditions for a short period of time when the inflaton is close to the critical scale. Accordingly, the Hubble horizon is perturbed and affects the dynamics of primordial cosmological perturbations. In particular, we analyze the angular power spectrum of B-mode polarization and find a boost on very large scales. We also find that the amplitude of scalar perturbations is suppressed near the critical scale. Thus our model provides an interpretation for the low-$\ell$ suppression of temperature anisotropies in the CMB power spectrum. We examine these effects and confront the model to observations.