The cosmological constant and quintessence

Abstract

The role of an effective repulsive cosmological constant (a false vacuum or quintessence) in the very early inflationary expansion and the recent accelerated stage of our universe is reviewed, and it is shown that the relict cosmological constant can significantly influence accretion phenomena in recent universe.Je podán přehled role efektivní kosmologické konstanty (falešného vakua nebo kvintesence) ve velmi rané inflační expanzi a současné urychlené expanzi našeho vesmíru. Je ukázáno,že reliktní kosmologická konstanta může silně ovlivňovat akreční procesy v současné epoše evoluce vesmíru. IntroductionRecent cosmological observations suggest that immediately after the big bang our universe experienced an extremely accelerated inflationary expansion, while at the present era the universe entered a second stage of accelerated expansion [Wang et al., 2000]. The rate of present acceleration is many orders of magnitude smaller than during the inflation in the very early universe, i.e., we can call it a microinflationary expansion.The inflationary cosmology is the first theory within which it is possible to predict the structure of the universe on large scale, based on causal physics, representing thus a promising way for connecting fundamental physics with experiment. It enables a natural explanation for almost all of the problems of the standard cosmology [Linde, 1990]. Especially, the mechanism by which initial quantum vacuum fluctuations develop into the large scale structure of the universe is tested by recent observations in deep detail [Bahcall et al., 1999].Usually, the inflationary models assume that during inflation potential energy density of a scalar (inflaton) field φ dominates the energy-momentum tensor, T µν ∼ g µν V (φ), i.e., we must have slowly rolling inflaton field with 1 2φ 2 V (φ). The limiting caseφ = 0 corresponds to de Sitter space with a repulsive cosmological constant.The current accelerated expansion can be explained either by a positive vacuum energy V (cosmological constant), or by a slowly rolling, quintessential scalar field. The acceleration mechanism is the same for the inflaton and quintessential fields. The inflaton field decays giving rise to the standard decelerated expansion. The behavior of the quintessential field in future is the key to the fate of our universe. Inflationary cosmologyThe inflationary cosmology is based on the hypothesis that there was an extremely short time interval, just after the Big Bang, beginning at some time t i and ending at the 'reheating time' t R during which the scale 1

Can we ever distinguish between quintessence and a cosmological constant?

“…Table I summarises the locations and the conditions for existence of the attractors. Here we construct an arbitrary quintessence potential from a series of time-slices of exponential potential (5) with varying λ (see [32,33] for asymptotic analyses). The dynamical attractors are thus known exactly at every instant.…”

Interacting dark energy: Decay into fermions

“…Since dark energy dilutes slower than matter we expect it to dominate the universe at late times if no fine tuning is assumed on the dark energy potential V and the universe will not stop the present stage of acceleration. However, this conclusion can be overcome by assuming a dark energy interaction [5].…”

“…In general fluids with w < −1 give many theoretically problems such as stability issues or wrong kinetic terms as phantom fields [11]. However, interacting dark energy [6]- [9], [5] is a very simple and attractive option which we will use in this letter. The interaction must be quite weak since dark energy particles have not been produced in the accelerator and because the dark energy has not decayed into lighter (e.g.…”

Attractor dynamics of inflationary monomial potentials

“…There exist several techniques to study the dynamical properties of cosmological scalar field, but one that has proved very useful is that of dynamical systems [2,3,4,5]. The dynamical system techniques can easily reveal the attractor properties of the solutions of the equations of motion.…”

“…One of the most studied is a model with an exponential scalar potential [5,3], because the equations of motion can easily be written as an autonomous dynamical system. However, sometimes the equations of motion result into a non-autonomous dynamical system, and then the properties of the dynamics are more involved and difficult to study.…”