Quintessence and the transition to an accelerating universe

Abstract

The implications of seven popular models of quintessence based on supergravity or M/string theory for the transition from a decelerating to an accelerating universe are explored. All seven potentials can mimic the ΛCDM model at low redshifts 0 ⩽ z ⩽ 5 . However, for a natural range of initial values of the quintessence field, the SUGRA and Polónyi potentials predict a transition redshift z t ≈ 0.5 for Ω Λ 0 = 0.70 , in agreement with the observational value z t ≈ 0.46 and in mild conflict with the ΛCDM value z t = 0.67 . Tables are given for the quintessence potentials for the recent average w ¯ 0 of the equation of state parameter, and for w 0 and w 1 in the low- z approximation w ≈ w 0 + w 1 z . It is argued that for the exponential potential e λ φ to produce a viable present-day cosmology, λ ⩽ 2 . A robust, scaled numerical method is presented for simulating the cosmological evolution of the scalar field.