Quintessence and the transition to an accelerating universe

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 zt≈0.5 for ΩΛ0=0.70, in agreement with the observational value zt≈0.46 and in mild conflict with the ΛCDM value zt=0.67. Tables are given for the quintessence potentials for the recent average w¯0 of the equation of state parameter, and for w0 and w1 in the low-z approximation w≈w0+w1z. It is argued that for the exponential potential eλφ 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.