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Cosmological acceleration. Dark energy or modified gravity?

Abstract

We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character,  More>>
Authors:
Publication Date:
May 15, 2006
Product Type:
Technical Report
Report Number:
DESY-06-063; ASTRO-PH-0605198
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCELERATION; COSMOLOGICAL MODELS; COSMOLOGY; FLUCTUATIONS; GALAXY CLUSTERS; GENERAL RELATIVITY THEORY; GRAVITATION; METRICS; NONLUMINOUS MATTER; PROGRESS REPORT; REVIEWS; SOLAR SYSTEM; SPACE-TIME; SYMMETRY; VACUUM STATES
OSTI ID:
20755510
Research Organizations:
Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
Other: ISSN 0418-9833; TRN: DE06F7228
Availability:
INIS
Submitting Site:
DEN
Size:
16 pages
Announcement Date:
Aug 11, 2006

Citation Formats

Bludman, S. Cosmological acceleration. Dark energy or modified gravity?. Germany: N. p., 2006. Web.
Bludman, S. Cosmological acceleration. Dark energy or modified gravity?. Germany.
Bludman, S. 2006. "Cosmological acceleration. Dark energy or modified gravity?" Germany.
@misc{etde_20755510,
title = {Cosmological acceleration. Dark energy or modified gravity?}
author = {Bludman, S}
abstractNote = {We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)}
place = {Germany}
year = {2006}
month = {May}
}