Gauged M-flation after BICEP2

A Ashoorioon,M.M Sheikh-Jabbari

doi:10.1016/j.physletb.2014.11.018

Abstract

In view of the recent BICEP2 results [arXiv:1403.3985] which may be attributed to the observation of B-modes polarization of the CMB with tensor-to-scalar ratio r=0.2−0.05+0.07, we revisit M-flation model. Gauged M-flation is a string theory motivated inflation model with Matrix valued scalar inflaton fields in the adjoint representation of a U(N) Yang–Mills theory. In continuation of our previous works, we show that for a class of M-flation models the action for these inflaton fields can be such that the “effective inflaton field” ϕ has a double-well Higgs-like potential, with minima at ϕ=0,μ. We focus on the ϕ>μ, symmetry-breaking region. We thoroughly examine predictions of the model for r in the 2σ region allowed for nS by the Planck experiment. As computed in [arXiv:0903.1481], for Ne=60 and nS=0.96 we find r≃0.2, which sits in the sweet spot of BICEP2 region for r. We find that with increasing μ arbitrarily, nS cannot go beyond ≃0.9670, the scalar spectral index for the quadratic chaotic potential. As nS varies in the 2σ range which is allowed by Planck and could be reached by the model, r varies in the range [0.13,0.26]. Future cosmological experiments, like the CMBPOL, that confines nS with σ(nS)=0.0029 can constrain the model further. Also, in this region of potential, for nS=0.9603, we find that the largest isocurvature mode, which is uncorrelated with curvature perturbations, has a power spectrum with the amplitude of order 10−11 at the end of inflation. We also discuss the range of predictions of r in the hilltop region, ϕ<μ.

Highlights

Inflation, and in particular slow-roll inflation, has emerged as the leading framework to understand and explain the recent cosmological CMB observations, most notably by PLANCK mission [1] and BICEP2 [2]
M-flation is a many-field inflationary model that could be realized within string theory from the dynamics of a stack of D-branes exposed to the six dimensional flux configuration
Requiring the 10 dimensional background to be a solution to the supergravity equations, forces the shape of the potential to be a symmetry-breaking double-well potential

Summary

Introduction

In particular slow-roll inflation, has emerged as the leading framework to understand and explain the recent cosmological CMB observations, most notably by PLANCK mission [1] and BICEP2 [2]. M-flation potential is protected by the supersymmetry of the bulk [15] It does not suffer from super-cutoff field roaming and falling into the eternal inflation phase because the spectrum of its fields around the effective single field model is not degenerate and all the modes around the classical inflationary path (which constitute 5N2 − 1 modes in gauged M-flation) have a hierarchical mass spectrum [13]. This hierarchical mass of isocurvature modes is the distinctive feature of M-flation compared to other multi-filed models like Nflation. This is still not clear to the authors of this paper how an axion with infinite decay constant as occurs in the above constructions are consistent with [10]

Quick review of gauged M-flation

Concluding remarks