LAUSR

We study the evolution of the energy distribution and equation of state of the Universe from the end of inflation until the onset of either radiation domination (RD) or a transient period of matter domination (MD). We use both analytical techniques and lattice simulations. We consider two-field models where the inflaton Φ has a monomial potential after inflation V (Φ) ∝ |Φ− v| (p ≥ 2), and is coupled to a daughter field X through a quadratic-quadratic interaction gΦX. We consider two situations, depending on whether the potential has a minimum at i) v = 0, or ii) v > 0. In the scenario i), the final energy transferred to X is independent of g and entirely determined by p: it is negligible for p < 4, and of order ∼ 50% for p ≥ 4. The system goes to MD at late times for p = 2, while it goes to RD for p > 2. In the later case, we can calculate exactly the number of e-folds until RD as a function of g, and hence predict accurately inflationary observables like the scalar tilt ns and the tensor-to-scalar ratio r. In the scenario ii), the energy is always transferred completely to X for p > 2, as long as its effective mass mX = g (Φ − v) is not negligible. For p = 2, the final ratio between the energy densities of X and Φ depends strongly on g. For all p ≥ 2, the system always goes to MD at late times.