Direct measurement of evolving dark energy density and super-accelerating expansion of the universe

Abstract

A higher value of Hubble constant has been obtained from measurements with nearby Type Ia supernovae, than that obtained at much higher redshift. With the peculiar motions of their hosts, we find that the matter content at such low redshift is only about 10% of that at much higher redshifts; such a low matter density cannot be produced from density perturbations in the background of the \Lambda CDM expansion. Recently the Planck team has reported a lower Hubble constant and a higher matter content. We find that the dark energy density increases with cosmic time, so that its equation-of-state parameter decreases with cosmic time and is less than -1 at low redshift. Such dark energy evolution is responsible for driving the super-accelerating expansion of the universe. In this extended \Lambda CDM model, the cosmological redshift represents time rather than radial coordinate, so that the universe complies to the Copernican Principle.