Dark torsion as the cosmic speed-up

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Abstract

It is shown that the recently detected acceleration of the universe can be understood by considering a modification of the teleparallel equivalent of General Relativity (TEGR), with no need of dark energy. The solution also exhibits phases dominated by matter and radiation as expected in the standard cosmological evolution. We perform a joint analysis with measurements of the most recent type Ia supernovae (SNe Ia), Baryon Acoustic Oscillation (BAO) peak and estimates of the CMB shift parameter data to constraint the only new parameter this theory has.

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Introduction to Modified Gravity and Gravitational Alternative for Dark Energy

S. Odintsov, S Nojiri (2006)

We review various modified gravities considered as gravitational alternative for dark energy. Specifically, we consider the versions of \(f(R)\), \(f(G)\) or \(f(R,G)\) gravity, model with non-linear gravitational coupling or string-inspired model with Gauss-Bonnet-dilaton coupling in the late universe where they lead to cosmic speed-up. It is shown that some of such theories may pass the Solar System tests. On the same time, it is demonstrated that they have quite rich cosmological structure: they may naturally describe the effective (cosmological constant, quintessence or phantom) late-time era with a possible transition from decceleration to acceleration thanks to gravitational terms which increase with scalar curvature decrease. The possibility to explain the coincidence problem as the manifestation of the universe expansion in such models is mentioned. The late (phantom or quintessence) universe filled with dark fluid with inhomogeneous equation of state (where inhomogeneous terms are originated from the modified gravity) is also described.

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The Case for a Positive Cosmological Lambda-term

Varun Sahni, Alexei Starobinsky (1999)

Recent observations of Type 1a supernovae indicating an accelerating universe have once more drawn attention to the possible existence, at the present epoch, of a small positive Lambda-term (cosmological constant). In this paper we review both observational and theoretical aspects of a small cosmological Lambda-term. We discuss the current observational situation focusing on cosmological tests of Lambda including the age of the universe, high redshift supernovae, gravitational lensing, galaxy clustering and the cosmic microwave background. We also review the theoretical debate surrounding Lambda: the generation of Lambda in models with spontaneous symmetry breaking and through quantum vacuum polarization effects -- mechanisms which are known to give rise to alarge value of Lambda hence leading to the `cosmological constant problem'. More recent attempts to generate a small cosmological constant at the present epoch using either field theoretic techniques, or by modeling a dynamical Lambda-term by scalar fields are also extensively discussed. Anthropic arguments favouring a small cosmological constant are briefly reviewed. A comprehensive bibliography of recent work on Lambda is provided.

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Disappearing cosmological constant in f(R) gravity

Alexei Starobinsky (2007)

For higher-derivative f(R) gravity where R is the Ricci scalar, a class of models is proposed which produce viable cosmology different from the LambdaCDM one at recent times and satisfy cosmological, Solar system and laboratory tests. These models have both flat and de Sitter space-times as particular solutions in the absence of matter. Thus, a cosmological constant is zero in flat space-time, but appears effectively in a curved one for sufficiently large R. A 'smoking gun' for these models would be small discrepancy in values of the slope of the primordial perturbation power spectrum determined from galaxy surveys and CMB fluctuations. On the other hand, a new problem for dark energy models based on f(R) gravity is pointed which is connected with possible overproduction of new massive scalar particles (scalarons) arising in this theory in the very early Universe.

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Publication date Created: 05 December 2008

Publication date Updated: 2009-05-21

Article

DOI: 10.1103/PhysRevD.79.124019

ArXiV ID: 0812.1205

SO-VID: d87d10a4-ed64-40f9-918e-d18ef1e4c632

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http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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Journal reference Phys.Rev.D79:124019,2009

Comments 5 pages, 5 figures, replaced to match version to be published in Physical Review D

Dark torsion as the cosmic speed-up

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Abstract

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Procedural speed in criminal law

Most cited references 6

Introduction to Modified Gravity and Gravitational Alternative for Dark Energy

The Case for a Positive Cosmological Lambda-term

Disappearing cosmological constant in f(R) gravity

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