Thermal balance in decaying $\mathsf{\Lambda}$ cosmologies

Abstract

We consider cosmological models in which the vacuum decay energy is channeled exclusively into radiation. We investigate the thermal evolution of the Universe with a variable cosmological term which varies as a function of the scale factor a as . Using constraints given by the temperature measurements of the cosmic microwave background, at redshifts between and , we find that models are clearly ruled out. The influence on the thermal decoupling between matter and radiation is also discussed.