Primordial universe with the running cosmological constant

Abstract

Theoretically, the running of the cosmological constant in the IR region is not ruled out. On the other hand, from the QFT viewpoint, the energy released due to the variation of the cosmological constant in the late Universe cannot go to the matter sector. For this reason, the phenomenological bounds on such a running are not sufficiently restrictive. The situation can be different in the early Universe when the gravitational field was sufficiently strong to provide an efficient creation of particles from the vacuum. We develop a framework for systematically exploring this possibility. It is supposed that the running occurs in the epoch when the Dark Matter already decoupled and is expanding adiabatically, while the usual matter should be regarded approximately massless and can be abundantly created from vacuum due to the decay of vacuum energy. By using the handy model of Reduced Relativistic Gas for describing the warm Dark Matter, we consider the dynamics of both cosmic background and linear perturbations and evaluate the impact of the vacuum decay on the matter power spectrum and to the first CMB peak. Additionally, using the combined SNIa+BAO data, we find the best-fit values for the free parameters of the model.

Cosmological framework for renormalization group extended gravity at the action level

“…The integration constants C 1 and C 2 above are the same that appear in the ψ solution (72). The GR solution is clearly recovered in the limit ν → 0 [50].…”

“…There are different frameworks on scale-dependent couplings and G at cosmological level. The majority con-siders the implementation of RG-like effects at the level of the field equations, or partially at the action level, (e.g., [3,12,25,26,71,72]). 5 Here we presented a framework in which all the relevant information come from the action, including the scale settings, and applied it to cosmology; leading to a picture that is different from both GR and well known modified gravity theories, as f (R).…”

“…Besides the evolution of the perturbation ψ, it is also relevant to understand how matter perturbations evolve. From the time-time component of the perturbative field equations (67), and using the ψ solution for dust (72), it is possible to find an explicit result for the density contrast δ ε , with…”

Cosmological constraints on entropic cosmology with matter creation

“…In [131,132], γ has been constrained by using entropic force models combined the variation of fundamental constants and it results to be ∼ 10 −4 − 10 −2 , which is completely different from the theoretical expectations. In literature [45,[133][134][135][136][137][138][139][140][141] one can find "similar" parameters, i.e. related to energy exchange phenomena, although they do not point to the system "boundary-bulk" but to energy exchanges among cosmological fluids.…”

Qualitative dynamics of interacting vacuum cosmologies

“…Instead we allow the vacuum to exchange energy with dark matter, leading to an alternative scenario with a time-dependent vacuum energy [6][7][8][9][10][11][12][13][14][15][16][17]. Such a time-dependent vacuum energy can arise from renormalization group running of the vacuum energy, which may also lead to running of Newton's gravitational constant [12,18,19], although we do not consider such effects here. Similarly we do not include restrictions on the nature of the energy transfer in such models [20].…”