Surface Reheating as a New Paradigm

Finite temperature effects are important to be considered in the early Universe. Given the fact that there is no direct evidence for the particle content in the early Universe beyond the Standard Model (SM) of electroweak scale ∼ 100 GeV, and in cosmology there is no direct evidence of thermal history beyond the era of Big Bang Nucleosynthesis (BBN) ∼ 1 MeV, it becomes a challenging problem understanding the physics of the very early Universe. In spite of this there are numerous observational hints which suggests the extension of the physics beyond the SM. It is also paramount to keep in mind that in an expanding Universe the local thermodynamical equilibrium can be achieved only if the particle interactions, or at much higher energy scales string interactions, or interactions between non-perturbative objects such as D-branes are first of all well known, and then their respective interaction rates follow: Γi(T ) ≥ H(T ). A simple example will illustrate our point. For 2 → 2 particle interactions the scattering rate is given by Γ ∼ αT (α is a coupling constant), which becomes smaller than H ∼ T 2/MP (we use reduced Planck scale MP = 2.436 × 10 18 GeV) at sufficiently high temperatures. It was noticed that elastic 2 → 2 processes maintain thermal equilibrium typically only up to Tmax ∼ 10 14 GeV, while chemical equilibrium is lost already at T ∼ 10 GeV . In N = 1 su-