Pre-inflationary clues from String Theory?

N Kitazawa,A Sagnotti

doi:10.1088/1475-7516/2014/04/017

Abstract

``Brane supersymmetry breaking'' occurs in String Theory when the only available combinations of D-branes and orientifolds are not mutually BPS and yet do not introduce tree-level tachyon instabilities. It is characterized by the emergence of a steep exponential potential, and thus by the absence of maximally symmetric vacua. The corresponding low-energy supergravity admits intriguing spatially-flat cosmological solutions where a scalar field is forced to climb up toward the steep potential after an initial singularity, and additional milder terms can inject an inflationary phase during the ensuing descent. We show that, in the resulting power spectra of scalar perturbations, an infrared suppression is typically followed by a pre-inflationary peak that reflects the end of the climbing phase and can lie well apart from the approximately scale invariant profile. A first look at WMAP9 raw data shows that, while the χ2 fits for the low-ℓ CMB angular power spectrum are clearly compatible with an almost scale invariant behavior, they display nonetheless an eye-catching preference for this type of setting within a perturbative string regime.

Highlights

It would be bizarre if Supersymmetry [1] were not to play a role in the Fundamental Interactions, since its local realization in Supergravity [2] and its completion in String Theory [3] contain profound lessons on the links between gravity and the other forces
A proper understanding of supersymmetry breaking cannot forego a detailed grasp of general matter couplings in Supergravity, which has long been available for models with N = 1 supersymmetry in four dimensions [6] but is not nearly as complete in the higher–dimensional settings that are so important in String Theory
Among a multitude of available vacua, String Theory suggests some peculiar options related to orientifold models where supersymmetry is broken at the string scale [7]

Summary

Introduction

It would be bizarre if Supersymmetry [1] were not to play a role in the Fundamental Interactions, since its local realization in Supergravity [2] and its completion in String Theory [3] contain profound lessons on the links between gravity and the other forces. If you will, that the low–l CMB data are opening in front of our instruments a small window on the onset of inflation, the very phenomenon that is usually advocated to explain the apparent flatness and homogeneity of our Universe and explains naturally the slight tilt of the CMB power spectrum [25] that was recently confirmed to high precision by PLANCK [26] Working within this assumption, we shall begin to explore how far one can go in relating the available WMAP9 raw data [27] to the models at stake.

Climbing Scalars and String Theory

A New Look at the Power Spectra of Climbing Scalars

A First Look at the CMB

Conclusions

A On two–exponential potentials and String Theory