Despite the fact that a rigid Λ-term is a fundamental building block of the concordance ΛCDM model, we show that a large class of cosmological scenarios with dynamical vacuum energy density ρ Λ and/or gravitational coupling G, together with a possible non-conservation of matter, are capable of seriously challenging the traditional phenomenological success of the ΛCDM. In this paper, we discuss these "running vacuum models" (RVM's), in which ρ Λ = ρ Λ (H) consists of a nonvanishing constant term and a series of powers of the Hubble rate. Such generic structure is potentially linked to the quantum field theoretical description of the expanding Universe. By performing an overall fit to the cosmological observables SNIa+BAO+H(z)+LSS+BBN+CMB (in which the WMAP9, Planck 2013 and Planck 2015 data are taken into account), we find that the class of RVM's appears significantly more favored than the ΛCDM, namely at an unprecedented level of 4.2σ. Furthermore, the Akaike and Bayesian information criteria confirm that the dynamical RVM's are strongly preferred as compared to the conventional rigid Λ-picture of the cosmic evolution. Subject headings: dark energy-dark matter-large-scale structure of universe
Recently there have been claims on model-independent evidence of dynamical dark energy. Herein we consider a fairly general class of cosmological models with a time-evolving cosmological term of the form Λ(H) = C 0 + C H H 2 + CḢḢ, where H is the Hubble rate. These models are well motivated from the theoretical point of view since they can be related to the general form of the effective action of quantum field theory in curved spacetime. Consistency with matter conservation can be achieved by letting the Newtonian coupling G change very slowly with the expansion. We solve these dynamical vacuum models and fit them to the wealth of expansion history and linear structure formation data. The results of our analysis indicate a significantly better agreement as compared to the concordance ΛCDM model, thus supporting the possibility of a dynamical cosmic vacuum.
The cosmological term, Λ, was introduced 104 years ago by Einstein in his gravitational field equations. Whether Λ is a rigid quantity or a dynamical variable in cosmology has been a matter of debate for many years, especially after the introduction of the general notion of dark energy (DE). Λ is associated to the vacuum energy density,
, and one may expect that it evolves slowly with the cosmological expansion. Herein we present a devoted study testing this possibility using the promising class of running vacuum models (RVMs). We use a large string SNIa+BAO+H(z)+LSS+CMB of modern cosmological data, in which for the first time the CMB part involves the full Planck 2018 likelihood for these models. We test the dependence of the results on the threshold redshift
at which the vacuum dynamics is activated in the recent past and find positive signals up to
for
. The RVMs prove very competitive against the standard ΛCDM model and give a handle for solving the
tension and alleviating the H
0 one.
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