Bare mass effects on the reheating process after inflation

We consider the effects of a bare mass term for the inflaton, when the inflationary potential takes the form V(ϕ)= λϕ^k about its minimum with k ≥ 4. We concentrate on k=4, but discuss general cases as well. Further, we assume λϕ_ end^2 ≫ m_ϕ^2, where ϕ_ end is the inflaton field value when the inflationary expansion ends. We show that the presence of a mass term (which may be present due to radiative corrections or supersymmetry breaking) can significantly alter the reheating process, as the equation of state of the inflaton condensate changes from w_ϕ=1/3 to w_ϕ=0 when λϕ^2 drops below m_ϕ^2. We show that for a mass m_ϕ≳ T_ RH/250, the mass term will dominate at reheating. We compute the effects on the reheating temperature for cases where reheating is due to inflaton decay (to fermions, scalars, or vectors) or to inflaton scattering (to scalars or vectors). For scattering to scalars and in the absence of a decay, we derive a strong upper limit to the inflaton bare mass m_ϕ < 350  MeV (T_ RH/10^10  GeV)^3/5, as there is always a residual inflaton background which acts as cold dark matter. We also consider the effect of the bare mass term on the fragmentation of the inflaton condensate.