Dynamical vacuum energy in the expanding Universe confronted with observations: a dedicated study

Abstract

Despite the many efforts, our theoretical understanding of the ultimate nature of the dark energy component of the universe still lags well behind the astounding experimental evidence achieved from the increasingly sophisticated observational tools at our disposal. While the canonical possibility is a strict cosmological constant, or rigid vacuum energy density ρ Λ =const., the exceeding simplicity of this possibility lies also at the root of its unconvincing theoretical status, as there is no explanation for the existence of such constant for the entire cosmic history. Herein we explore general models of the vacuum energy density slowly evolving with the Hubble function H and/or its time derivative, ρ Λ = ρ Λ (H,Ḣ). Some of these models are actually well-motivated from the theoretical point of view and may provide a rich phenomenology that could be explored in future observations, whereas some others have more limitations. In this work, we put them to the test and elucidate which ones are still compatible with the present observations and which ones are already ruled out. We consider their implications on structure formation, in combination with data on type Ia supernovae, the Cosmic Microwave Background, the Baryonic Acoustic Oscillations, and the predicted redshift distribution of cluster-size collapsed structures. The relation of these vacuum models on possible evidence of dynamical dark energy recently pointed out in the literature is also briefly addressed. Keywords: dynamical dark energy, cosmological constant, structure formation. arXiv:1409.7048v3 [astro-ph.CO] 27 Nov 2014 7.1 Generalized Press-Schechter formalism 40 7.2 Numerical results: number counts of the dynamical vacuum models 45 8. Discussion and conclusions 48 A. Understanding how the cluster number counts method works 51 B. Computing the collapse density threshold δ c for the dynamical vacuum models 53 B.1 Type-A models 54 B.2 Type-B models 55 B.3 Numerical procedure to determine δ c 55 -1 -1 The linear terms also appear if nonperturbative infrared effects would be possible in the cosmological

Cosmology with Varying Constants from a Thermodynamic Viewpoint

“…We have found the observational bound on the free parameter γ, which is taken to the order of unity on the theoretical background. Our analysis shows that it should be on the order of 10 −2 − 10 −4 , and this is consistent with the results obtained in [31]. Similarly, we have found the bound on the variability of c and G. Our analysis shows that both c and G are increasing with the evolution of the universe in the entropic description.…”

“…We compare our model with the data from supernovae, Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB). Our model is also related to dynamical vacuum energy models, which have been discussed and confronted with data [11][12][13][14][30][31][32]. Similarly, dynamical dark energy models with varying fundamental constants have been discussed in [33,34].…”

“…If we use the ansätze c = c 0 a n and G = G 0 a q in the above-modified equations of motion, then these equations are analogous to the entropic force expressions [15][16][17] and running vacuum models [11][12][13][14][30][31][32]. We consider the multiple fluid scenario, and using the barotropic equation of state p i = w i ρ i , we solve the modified continuity equation…”

Starobinsky-Like Inflation and Running Vacuum in the Context of Supergravity

“…Specifically, we wish to show that the behaviour of the aforementioned SUGRA scenario effectively mimics the RVM. Once this link is elucidated, the general "decaying" vacuum description inherent to the RVM formulation allows one to smoothly connect inflation to the standard Fridman-Lemaître-Robertson-Walker (FLRW) radiation era, which subsequently proceeds into a matter and dark energy domination in the present era, in which it still carries a mild dynamical behaviour compatible with the current cosmological data [29,30]. Such an expansion history of the Universe has been put forward in previous works by the authors in various collaborations and contexts, e.g., non-equilibrium string-inspired cosmologies [44][45][46] or conventional field-theoretic cosmologies in which the above-mentioned RVM is extensively applied for the study of the early cosmic history [23][24][25][26]28].…”

“…The implications of these dynamical vacuum models have recently been analysed both for the early Universe [22][23][24][25][26][27][28], as well as for the phenomenology of the current Universe [29][30][31]; see also [32][33][34][35][36][37][38][39][40] for previous analyses.…”