March 09, 2006

Surface Paradigm for Dark Energy

There has been indications that the dark energy and dark matter have their origin in general relativity, with some extensions. T.Padmanabhan discusses dark energy as the Mystery of the Millennium (an optimist would hope a decade or two). Dark matter discussion is given in the references of this paper.

The author assumes the dynamics of gravity follows from an approach which uses only the surface term of the Hilbert action for the continuum. Gravity has thermodynamic origin in this approach. The surface term's variation is related to entropy TdS and the matter term's variation gives PdV and dE terms. The entire variation is equivalent to the known equality between these. The main point I quote and condense:

Within the true theory of quantum gravity, measurable quantities should be the fluctuations in the vacuum energy and not the absolute value of the vacuum energy. The cosmological constant is most likely a low energy relic of quantum gravitational effects, arising from the surface term alone. This procedure is applicable to a large class of theories, including Gauss-Bonnet type actions in higher dimensions (superstrings). This suggests that the mechanism for ignoring the bulk cosmological constant is likely to survive quantum gravitational corrections which are likely to bring in additional, higher derivative, terms to the action. In a universe with two length scales L_Lambda (proportional to the Hubble radius) and L_p, the vacuum fluctuations will contribute an energy density of the correct order of magnitude r_DE =√rho_IR rho_UV, according to the author.
Addendum (more refs.)