Running vacuum cosmological models: linear scalar perturbations

Abstract

In cosmology, phenomenologically motivated expressions for running vacuum are commonly parametrized as linear functions Λ(H 2 ) or Λ(R). Such kind of models assume an equation of state for vacuum given by P Λ = − ρ Λ , relating their background pressure P Λ and mean energy density ρ Λ ≡ Λ/8πG. This equation of state requires that the dynamic for vacuum is due to the energy exchange with the material species. Most of the approaches to background level consider only the energy exchange between vacuum and the transient dominant material component of the universe. We extend such models assuming the running vacuum as the sum of independent contributions ρ Λ = i ρ Λi , associated with (and interacting with) each of the i material species. We derive the linear scalar perturbations for two running scenarios, modeling its cosmic evolution and identifying their different imprints on the cosmic microwave background anisotropies and the matter power spectrum. In the Λ(H 2 ) scenario the running vacuum are coupled with all the material species in the universe, whereas the Λ(R) description only leads to coupling between vacuum and the non-relativistic matter components; which produces different imprints of the two models on the matter power spectrum. A comparison with the Planck 2015 data was made in order to constrain the free parameters of the models. In the case of the Λ(H 2 ) model, it was found that Ω Λ = 0.705 ± 0.027 and H 0 = 69.6 ± 2.9 km M pc −1 s −1 , which diminish the tension with the low redshift expectations. * elduartep@usp.br †

Cosmological constant vis-à-vis dynamical vacuum: Bold challenging the ΛCDM

“…The bounds on the vacuum parameters from the analysis of cosmic perturbations, including the power spectrum, are also compatible with the fitting results presented here, cf [58]…”

“…Since, as mentioned, Ω b /Ω dm ≃ 0.1, we can neglect the square of this quantity and rewrite (58) in the more compact form…”

Density perturbations for running vacuum: a successful approach to structure formation and to the σ8-tension

“…As a consequence, the LSS formation is substantially suppressed at low scales with respect to the ΛCDM and in this way the tension with the f (z)σ8(z) data loosens, mainly due to an important decrease of the σ8 parameter. Let us stress that such feature cannot be appraised if one restricts the analysis mostly to the CMB without sufficient LSS input (Heavens et al 2017;Perico & Tamayo 2017).…”

Running vacuum against the H 0 and σ8 tensions

“…Here, however, we will concentrate on the post-inflationary universe, where only the leading power ∼ H 2 is involved in the dynamics of ρ vac . A variety of phenomenological analyses have supported this possibility in recent years and within different approaches [13][14][15][16][17][18][19].…”