Late-time Entropy Production from Scalar Decay and Neutrino Decoupling

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Late-time entropy production from scalar decay arises in scenarios like thermal inflation, proposed to dilute long-lived, massive fields like the gravitino and the moduli. The scalar decay may continue into Mev-scale temperatures and affect BB nucleosynthesis. The effect of such entropy production on electron neutrino decoupling is studied. A lower bound of about 10(-22) Gev is estimated for the scalar decay constant, such that, for higher values of the decay constant, standard electron neutrino decoupling is unaffected.