CMB Imprints of a Pre-Inflationary Climbing Phase

TL;DR

This paper explores how a pre-inflationary climbing phase, inspired by string theory models with SUSY breaking, could leave observable imprints on the CMB, potentially explaining large-angle anomalies.

Contribution

It introduces a novel pre-inflationary dynamics model based on string theory, analyzing its effects on CMB observables and their statistical significance.

Findings

Pre-inflationary climbing phase can suppress scalar power spectrum.

Enhanced tensor spectrum and oscillations may occur due to initial-state effects.

Possible explanation for large-angle CMB anomalies.

Abstract

We discuss the implications for cosmic microwave background (CMB) observables, of a class of pre-inflationary dynamics suggested by string models where SUSY is broken due to the presence of D-branes and orientifolds preserving incompatible portions of it. In these models the would-be inflaton is forced to emerge from the initial singularity climbing up a mild exponential potential, until it bounces against a steep exponential potential of "brane SUSY breaking" scenarios, and as a result the ensuing descent gives rise to an inflationary epoch that begins when the system is still well off its eventual attractor. If a pre-inflationary climbing phase of this type had occurred within 6-7 e-folds of the horizon exit for the largest observable wavelengths, displacement off the attractor and initial-state effects would conspire to suppress power in the primordial scalar spectrum, enhancing it in the tensor spectrum and typically superposing oscillations on both. We investigate these imprints on CMB observables over a range of parameters, examine their statistical significance, and provide a semi-analytic rationale for our results. It is tempting to ascribe at least part of the large-angle anomalies in the CMB to pre-inflationary dynamics of this type.