Abstract
We study constraints from the latest cosmic microwave background (CMB), large-scale structure (2dF, Abell/ACO, PSCz) and SN1a data on dark energy models with a sharp transition in their equation of state, w(z). Such a transition is motivated by models like vacuum metamorphosis where non-perturbative quantum effects are important at late times. We allow the transition to occur at a specific redshift, zt, to a final negative pressure −1 ⩽wf < −1/3. We find that the CMB and supernovae data, in particular, prefer a late-time transition because of the associated delay in cosmic acceleration. The best fits (±1 σ errors) to all the data are zt= 2.0+2.2−0.76, ΩQ= 0.73+0.02−0.04 and wf=−1+0.2. For zt > 5 the likelihood becomes flat, asymptoting to the standard ΛCDM model.
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