Degeneracy pressure of relic neutrinos and cosmic coincidence problem

Abstract

We consider the universe as a huge $\nu_R$-sphere formed with degenerate relic neutrinos and suggest that its constant energy density play a role of an effective cosmological constant. We construct the sphere as a bubble of true vacuum in a field theory model with a spontaneously broken U(1) global symmetry, and we interpret the sphere-forming time as the transition time for recent acceleration of the universe. The coincidence problem may be regarded as naturally resolved in this model, because the relic neutrinos can make the $\nu_R$-sphere at the recent past time during the matter-dominated era.