On the lifetime of a cold dark matter particle and the cosmological diffuse photon background

We show that a Majorana heavy neutrino with a mass O(100TeV) is a good candidate particle for cold dark matter. It can be responsible for the majority of the cosmological diffuse photon background owing to lifetime of the order of O(10^(25)s), dominantly fixed by the radiative two-body decay. The lifetime is suppressed by two mechanisms: the leptonic GIM cancellation and the see-saw weak coupling suppression. As a fermion cold dark matter particle, a heavy neutrino favours the average mass density of the Universe constrained by the Einstein-Cartan cosmology.