Current constraints on the dark energy equation of state

Abstract

We combine complementary datasets from Cosmic Microwave Background (CMB) anisotropy measurements, high redshift supernovae (SN-Ia) observations and data from local cluster abundances and galaxy clustering (LSS) to constrain the dark energy equation of state parameterized by a constant pressure-to-density ratio $w_Q$. Under the assumption of flatness, we find $w_Q < -0.85$ at 68% c.l., providing no significant evidence for quintessential behaviour different from that of a cosmological constant. We then generalise our result to show that the constraints placed on a constant $w_{Q}$ can be safely extended to dynamical theories. We consider a variety of quintessential dynamical models based on inverse power law, exponential and oscillatory scaling potentials. We find that SN1a observations are `numbed&#39; to dynamical shifts in the equation of state, making the prospect of reconstructing $w(z)$, a challenging one indeed.