Dynamical dark energy: Scalar fields and running vacuum

Recent analyses in the literature suggest that the concordance Lambda CDM model with rigid cosmological term, Lambda = const. may not be the best description of the cosmic acceleration. The class of running vacuum models, in which Lambda = Lambda(H) evolves with the Hubble rate, has been shown to fit the string of SNIa+ BAO+ H(z)+ LSS+ CMB data significantly better than the Lambda CDM. Here, we provide further evidence on the time- evolving nature of the dark energy (DE) by fitting the same cosmological data in terms of scalar fields. As a representative model, we use the original Peebles and Ratra potential, V proportional to phi(-alpha). We find clear signs of dynamical DE at similar to 4 sigma c.l., thus reconfirming through a nontrivial scalar field approach the strong hints formerly found with other models and parametrizations.