The $\bar{\Lambda}{\rm CDM}$ cosmology: From inflation to dark energy through running Λ

Abstract

Perhaps the deepest mystery of our accelerating universe in expansion is the existence of a tiny and rigid cosmological constant, Λ. Its size is many orders of magnitude below the expected one in the standard model of particle physics. This is a very welcome fact, namely if we care at all about our own existence and fate. However, we do not have a minimally satisfactory explanation for our good fortune and for the failing of the SM at that crucial point. To start with, an expanding universe is not expected to have a static vacuum energy density. We should rather observe a mildly dynamical behavior δΛ(t) ~ R ~ H2(t) with the expansion rate H. At the same time, it is natural to think that the huge value of the primeval vacuum energy (presumably connected to some GUT) was responsible for the initial inflationary phase. In the traditional inflaton models such phase is inserted by hand in the early epoch of the cosmic evolution, and it is assumed to match the standard ΛCDM regime during the radiation epoch. Here, instead, we consider a class of dynamical vacuum models which incorporate in a single vacuum structure [Formula: see text] the rapid stage of inflation, followed by the radiation and cold matter epochs, until achieving our dark energy universe. The early behavior of such "running vacuum model" [Formula: see text] bares resemblance with Starobinsky's inflation in the early universe and is very close to the concordance model for the entire post-inflationary history. Most remarkably, the inflationary period in the [Formula: see text] terminates with "graceful exit" and the large entropy problem can be solved. The model is compatible with the latest cosmological data on Hubble expansion and structure formation, and at the same time presents distinctive observational features that can be tested in the near future.

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

“…The smaller is M in Planck mass units (i.e., the larger is the dimensionless parameter m 2 P /M 2 in front of R 2 ), the longer is the inflationary time (cf. Figure 2 of [22]). Of course, M cannot be much below the natural scale of inflation, and in fact, it should be of the same order, i.e., M ∼ M X , where M X is some GUT scale below the Planck mass.…”

“…It is the purpose of this work to go one step further from demonstrating the compatibility of the dynamically-broken SUGRA scenario [7][8][9] with inflation and to discuss the possibility of a dynamical evolution of the inflationary phase ground state to the standard radiation regime within the context of the running vacuum model (RVM) of the cosmic evolution utilizing an effective "re-normalization group (RG) approach"; see [13][14][15] and [20][21][22] for comprehensive expositions. Specifically, we wish to show that the behaviour of the aforementioned SUGRA scenario effectively mimics the RVM.…”

“…of (4) can be richer [22]; however, the canonical possibility is the previous one, and hereafter, we restrict to it. The coefficients a i , b i , c i .…”

“…Also very important for our considerations is the framework of the running vacuum model (RVM) [13][14][15][16][17][18][19]; see [20][21][22] and the references therein for a recent detailed exposition. 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.…”

“…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.…”