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 in the M-flation model induced from a supersymmetric 10d background probed by a stack of N D3-branes , the “ effective inflaton ” \phi has a double-well Higgs-like potential , with minima at \phi = 0 , \mu .
We focus on the \phi > \mu , symmetry-breaking region .
We thoroughly examine predictions of the model for r in the 2 \sigma region allowed for n _ { S } by the Planck experiment .
As computed in [ arXiv:0903.1481 ] , for N _ { e } = 60 and n _ { S } = 0.96 we find r \simeq 0.2 , which sits in the sweet spot of BICEP2 region for r .
We find that with increasing \mu arbitrarily , n _ { S } can not go beyond \simeq 0.9670 .
As n _ { S } varies in the 2 \sigma range which is allowed by Planck and could be reached by the model , r varies in the range [ 0.1322 , 0.2623 ] .
Future cosmological experiments , like the CMBPOL , that confines n _ { S } with \sigma ( n _ { S } ) = 0.0029 can constraint the model further .
Also , in this region of potential , for n _ { S } = 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 , \phi < \mu .