Neutrino decay and the thermochemical equilibrium of the interstellar medium

We calculate the thermochemical equilibrium of the diffuse interstellar medium, including ionization by a photon flux Fν from neutrino decay. The main heating mechanism considered is photoelectrons from grains and PAHs. For the studied range of Fν values, there always exists two regions of stability (a warm and a cold phase) that can coexist in equilibrium if the thermal interstellar pressure is between a maximum value (Pmax) and a minimum value (Pmin). High Fν values (∼ 10 −10 cm s) can be consistent with observed interstellar pressures only if more efficient sources are heating the gas. It is shown that a neutrino flux increase (due, for example, to an increase in the supernova explosion rate) may stimulate the condensation of cold gas by decreasing Pmax below the interstellar pressure value.