A generalized parameterization w β (z) for the dark energy equation of state (EoS) is proposed and some of its cosmological consequences are investigated. We show that in the limit of the characteristic dimensionless parameter β → +1, 0 and -1 some well-known EoS parameterizations are fully recovered whereas for other values of β the proposed parameterization admits a wider and new range of cosmological solutions. We also discuss possible constraints on the w β (z) parameters from current observational data. PACS numbers: 98.80.Es, 98.80.-k, 98.80.Jk * Electronic address: edesio@on.br † Electronic address: alcaniz@on.br ‡ Electronic address: zhuzh@bnu.edu.cn § Electronic address: raimundosilva@dfte.ufrn.br 1 The possibility ω(z) = −1 still leads to two different routes, i.e., either the so-called quintessence if −1 < ω(z) < −1/3 [2] or phantom fields if ω(z) < −1 [3]. Both cases violate the strong energy condition ρ + 3p > 0, but the latter goes even further and also violates the null energy condition ρ + p > 0 [4].
Extending previous results [Phys. Rev. Lett. 97, 081301 (2006)], we explore the cosmological implications of a new quintessence scenario driven by a slow rolling homogeneous scalar field whose equation of state behaved as freezing over the entire cosmic evolution, is approaching −1 today, but will become thawing in the near future, thereby driving the Universe to an eternal deceleration. We argue that such a mixed behavior, named hybrid, may reconcile the slight preference of current observational data for freezing potentials with the impossibility of defining observables in the String/M-theory context due to the existence of a cosmological event horizon in asymptotically de Sitter universes as, e.g., pure freezing scenarios. PACS numbers: 98.80.Cq; 95.36.+x
We investigate the impact of a non-minimal coupling of the scalar field with gravity in inflationary models, where a small coupling is allowed. As a concrete example, we consider the Witten-O'Raifeartaigh model, where, in line with other models, the presence of a coupling strength ξ can recover concordance of the inflationary parameters with cosmic microwave background (CMB) constraints, provided by the Planck collaboration. We go beyond the slow-roll regime and investigate the impact in the description of CMB anisotropies by performing a statistical analysis of the model with the most recent Planck + Baryon Acoustic Oscillations (BAO) data to seek for any indication of a non-zero coupling by data within the model. We find that not only the presence of a non-minimal coupling is seen, but the model has a slight statistical preference when compared with the standard ΛCDM one. We also discuss the results on the minimally-coupled model, which in general, favours the simple setting where the associated mass scale is equal to the reduced Planck mass Mp while being, in general, disfavored concerning the standard model.
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