Self-tuning vacuum variable and cosmological constant

Abstract

A spacetime-independent variable is introduced which characterizes a Lorentz-invariant self-sustained quantum vacuum. For a perfect (Lorentz-invariant) quantum vacuum, the self-tuning of this variable nullifies the effective energy density which enters the low-energy gravitational field equations. The observed small but nonzero value of the cosmological constant may then be explained as corresponding to the effective energy density of an imperfect quantum vacuum (perturbed by, e.g., the presence of thermal matter).

Dynamic vacuum variable and equilibrium approach in cosmology

“…Ref. [1] and references therein). In addition, the matter energy-momentum tensor for the model universe is taken as that of a perfect fluid characterized by the energy density ρ M and isotropic pressure P M .…”

“…[1] in general terms. But a specific example was also given in terms of a four-form field strength F [3,4,5,6,7,8].…”

“…[3,4,5,6,7,8]). Such a quadratic function gives rise to a gas-like vacuum [1]. But a gas-like vacuum cannot exist in equilibrium without external pressure, as the equilibrium vacuum charge vanishes, q 0 = 0.…”

“…An example of an appropriate function ǫ(F ) will be 1 An extensive but nonexhaustive list of references to research papers and reviews on the so-called "cosmological constant problem(s)" can be found in Ref. [1]. A recent review on cosmic "dark energy" is given in Ref.…”

Notes on ghost dark energy

“…This numerical coincidence is impressive and also means that this model gets rid of fine tuning problem [8,9]. Actually, several authors have already suggested DE model with energy density proportional to Λ 3 QCD H in different physical contexts [15,16,17,18,19,20,21,39, 40] such as QCD trace anomaly, gluon condensate of quantum chromodynamics, modifying gravity and so on.…”