Gauged M-flation after BICEP2

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.