Crossing the phantom divide barrier with scalar tensor theories
Journal of Cosmology and Astroparticle Physics
There is accumulating observational evidence (based on SnIa data) that the dark energy equation of state parameter w may be evolving with time and crossing the phantom divide barrier w=-1 at recent times. The confirmation of these indications by future data would indicate that minimally coupled quintessence can not reproduce the observed expansion rate H(z) for any scalar field potential. Here we explicitly demonstrate that scalar tensor theories of gravity (extended quintessence) can predict
... ossing of the phantom divide barrier. We reconstruct phenomenologically viable scalar-tensor potentials F(Φ) and U(Φ) that can reproduce a polynomial best fit expansion rate H(z) and the corresponding dark energy equation of state parameter w(z) crossing the w=-1 line. The form of the reconstructed scalar tensor potentials is severely constrained but is not uniquely determined. This is due to observational uncertainties in the form of H(z) and also because a single observed function H(z) does not suffice for the reconstruction of the two potential functions F(Φ) and U(Φ).