Dynamic vacuum variable and equilibrium approach in cosmology

Abstract

A modified-gravity theory is considered with a four-form field strength F , a variable gravitational coupling parameter G(F ), and a standard matter action. This theory provides a concrete realization of the general vacuum variable q as the four-form amplitude F and allows for a study of its dynamics. The theory gives a flat Friedmann-Robertson-Walker universe with rapid oscillations of the effective vacuum energy density (cosmological "constant"), whose amplitude drops to zero asymptotically. Extrapolating to the present age of the Universe, the order of magnitude of the average vacuum energy density agrees with the observed near-critical vacuum energy density of the present universe. It may even be that this type of oscillating vacuum energy density constitutes a significant part of the so-called cold dark matter in the standard Friedmann-Robertson-Walker framework. PACS numbers: 04.20.Cv, 98.80.Jk, 95.35.+d, 95.36.+x

Reconsidering a higher-spin-field solution to the main cosmological constant problem

“…(5.16) of Ref. [7] (and reiterated in the review [10]), the present value of this quantity ½Ã þðt now Þ would be of the order of the experimental value à ðexpÞ $ ðmeVÞ 4 .…”

“…Inspiration for this model was obtained from previous work by Volovik and one of the present authors on the so-called q-theory approach [6][7][8][9] to the main cosmological constant problem (a one-page review of q-theory can be found in Appendix A of Ref. [10] and a ultrabrief summary will be given in the Footnote of Sec.…”

Analogue Gravity

“…However, it is remarkable that it matches its order of magnitude, (at least for the current epoch), albeit any dynamical model implementing this idea will probably have to do so only at late times to avoid possible tension with the observational data. Guided by these lessons, there are already a number of heuristic investigations about how a cosmological term could dynamically adapt to the evolution of the matter content, and which implications it could have for the evolution of the universe [27, 350, 349, 351]. …”

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.…”