Matrix Inflation and its String Theory Origins

Motivated by the dynamics of N coincident D3 branes in some specific flux compactifications, we construct an inflationary model in which inflation is driven by three N x N hermitian matrices (Phi(i), i = 1,2, 3, hence the name Matrix Inflation, or M-flation for short. We show that one can consistently restrict the classical dynamics to a sector in which the Phi(i) are proportional to the N x N irreducible representation of SU(2). In this sector our model behaves like an effective inflaton field, which takes super-Planckian field values, and 3N(2) - 1 isocurvature fields. These may have the observational effects such as production of iso-curvature perturbations on cosmic microwave background. Moreover, the existence of these extra scalars provides us with a natural preheating mechanism and exit from inflation. Due to the super-Planckian excursions of the canonical effective inflaton, the model is capable of producing a considerable amount of gravity waves that can be probed by future CMB polarization experiments. Furthermore, the fine-tunings associated with unnaturally small couplings in the chaotic type inflationary scenarios are removed. We also show that even if the cutoff of the theory is lowered by the square of number of species, one can still use the effective field theory approach to justify the absence of higher dimensional operators.