Decay of the vacuum energy into CMB photons

We examine the possibility of the decay of the vacuum energy into cosmic microwave background (CMB) photons. It is shown that observations of the primordial density fluctuation spectrum put strong limits on the possible decay rate. When photon creation due to the vacuum energy decay takes place, the standard linear temperature dependence, T(z)=T_0(1+z), where T_0 is the present CMB temperature, is modified. The decay is described by a generic temperature dependence, T(z)=T_0(1+z)^{1-\beta}, of the CMB photons. A strong limit on the maximum value of the decay rate is obtained by placing a maximum value on the \beta parameter: \beta_{max}\approx 3\times 10^{-3}.