The State of the Dark Energy Equation of State

By combining data from seven cosmic microwave background experiments with large scale structure data, the Hubble parameter measurement from the Hubble Space Telescope and luminosity measurements of Type Ia supernovae we demonstrate the bounds on the dark energy equation of state parameter $w_Q$ to be $-1.62< w_Q <-0.74$ at the 95% confidence level. Although our limit on $w_Q$ is improved with respect to previous analyses, cosmological data does not rule out the possibility that $w_Q$ is less than -1. We present a tracking model that ensures $w_Q \le -1$ at recent times and discuss the observational consequences.