Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-05-06
Phys.Lett.B624:147-157,2005
Astronomy and Astrophysics
Astrophysics
LaTeX, 15 pages, 3 figures. Extended discussion and references added. Version accepted in Physics Letters B
Scientific paper
10.1016/j.physletb.2005.08.051
While there is mounting evidence in all fronts of experimental cosmology for a non-vanishing dark energy component in the Universe, we are still far away from understanding its ultimate nature. A fundamental cosmological constant, Lambda, is the most natural candidate, but many dynamical mechanisms to generate an effective Lambda have been devised which postulate the existence of a peculiar scalar field (so-called quintessence, and generalizations thereof). These models are essentially ad hoc, but they lead to the attractive possibility of a time-evolving dark energy with a non-trivial equation of state (EOS). Most, if not all, future experimental studies on precision cosmology (e.g. the SNAP and PLANCK projects) address very carefully the determination of an EOS parametrized ``a la quintessence''. Here we show that by fitting cosmological data to an EOS of that kind can also be interpreted as a hint of a fundamental, but time-evolving, cosmological term: Lambda=Lambda(t). We exemplify this possibility by studying the effective EOS associated to a renormalization group (RG) model for Lambda. We find that the effective EOS can correspond to both normal quintessence and phantom dark energy, depending on the value of a single parameter of the RG model. We conclude that behind a non-trivial EOS of a purported quintessence or phantom scalar field there can actually be a running cosmological term of a fundamental quantum field theory.
Sola Joan
Stefancic Hrvoje
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