Asymmetric reheating from a symmetric inflationary potential

Abstract

We explore a model of two-field inflation with a power-law potential in which two identical matter sectors decoupled from each other may reheat to different temperatures while preserving the symmetry of the Lagrangian. This scenario is motivated by mirror dark matter models in which the temperature of the mirror sector is constrained to be ${T}^{\ensuremath{'}}\ensuremath{\lesssim}0.5\text{ }\text{ }\mathrm{T}$ by big bang nucleosynthesis and the cosmic microwave background. For powers $p<2$, we find that the symmetric field trajectory $X=Y$ is a repeller solution, such that any randomly occurring asymmetry in the initial conditions is amplified by many orders of magnitude during inflation, especially in a given class of models with nonminimal kinetic terms. Isocurvature fluctuations are strongly suppressed in this model, but a $\mathcal{O}(0.03--0.07)$ tensor-to-scalar ratio could be observed in the near future. The range of potential parameters compatible with Planck constraints is shown to be much larger than in corresponding single-field models. This occurs because the curved field trajectory at horizon crossing leads to a lower spectral index.