Thermal balance in decaying Λ cosmologies

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 Omega(Lambda) = Omega(Lambda,1) + Omega(Lambda,2) a(-m). Using constraints given by the temperature measurements of the cosmic microwave background, at redshifts between z = 0 and z = 4, we find that For Allm not equal 0 Omega(Lambda) = Omega(Lambda,0) a(-m) models are clearly ruled out. The influence on the thermal decoupling between matter and radiation is also discussed.