Mass-varying neutrinos from a variable cosmological constant

Abstract

We consider, in a completely model-independent way, the transfer of energy between thecomponents of the dark energy sector consisting of the cosmological constant (CC) and ofrelic neutrinos. We show that such a cosmological setup may promote neutrinos tomass-varying particles, thus resembling a recently proposed scenario of Fardon, Nelson, andWeiner (FNW), but now without introducing any acceleron-like scalar fields. Although aformal similarity of the FNW scenario with the variable CC one can be easilyestablished, one nevertheless finds different laws for neutrino mass variation in eachscenario. We show that as long as the neutrino number density dilutes canonically,only a very slow variation of the neutrino mass is possible. For neutrino massesto vary significantly (as in the FNW scenario), a considerable deviation fromthe canonical dilution of the neutrino number density is also needed. We notethat the present ‘coincidence’ between the dark energy density and the neutrinoenergy density can be obtained in our scenario even for static neutrino masses.