<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" display="inline" overflow="scroll"><mml:mi>R</mml:mi><mml:mo>+</mml:mo><mml:msup><mml:mrow><mml:mi>S</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:math> theories of gravity without big-bang singularity

Lu, Jia-An

doi:10.1016/j.aop.2015.01.013

Annals of Physics

2015

DOI: 10.1016/j.aop.2015.01.013

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R+S2 theories of gravity without big-bang singularity

Jia-An Lu

Abstract: The R + S 2 theories of gravity, where S 2 denotes the quadratic torsion terms, are analyzed under three cases. In the first two cases, the matter fields are described by two different spin fluids which are not homogeneous and isotropic. In the third case, a homogeneous and isotropic torsion field is used. It is found that under all the three cases, the R+S 2 theories may avert the big-bang singularity of the RobertsonWalker universe, with three corresponding constraints on the parameters.

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Cited by 5 publications

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Einstein-Cartan wormhole solutions

Mehdizadeh

Ziaie

2017

Phys. Rev. D

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In the present work we investigate wormhole structures and the energy conditions supporting them, in Einstein-Cartan theory ({\sf ECT}). The matter content consists of a Weyssenhoff fluid along with an anisotropic matter which together generalize the anisotropic energy momentum tensor in general relativity ({\sf GR}) to include spin effects. Assuming that the radial pressure and energy density obey a linear equation of state, we introduce exact asymptotically flat and anti-de-Sitter spacetimes that admit traversable wormholes and respect energy conditions. Such wormhole solutions are studied in detail for two specific forms for the redshift function, namely a constant redshift function and the one with power law dependency.Comment: 16 pages, 2 figure

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Einstein-Cartan wormhole solutions

Mehdizadeh

Ziaie

2017

Phys. Rev. D

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Dynamic wormhole solutions in Einstein-Cartan gravity

Mehdizadeh

Ziaie

2017

Phys. Rev. D

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In the present work we investigate evolving wormhole configurations described by a constant redshift function in Einstein-Cartan theory ({{\sf ECT}}). The matter content consists of a Weyssenhoff fluid along with an anisotropic matter which together generalize the anisotropic energy momentum tensor in general relativity ({{\sf GR}}) in order to include the effects of intrinsic angular momentum (spin) of particles. Using a generalized Friedmann-Robertson-Walker ({\sf FRW}) spacetime, we derive analytical evolving wormhole geometries by assuming a particular equation of state ({{\sf EoS}}) for energy density and pressure profiles. We introduce exact asymptotically flat and anti-de Sitter spacetimes that admit traversable wormholes and respect energy conditions throughout the spacetime. The rate of expansion of these evolving wormholes is determined only by the Friedmann equation in the presence of spin effects.Comment: 15 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:1704.0692

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Mimetic-metric-torsion with induced axial mode and phantom barrier crossing

2021

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We extend the basic formalism of mimetic-metric-torsion gravity theory, in a way that the mimetic scalar field can manifest itself geometrically as the source of not just the trace mode of torsion, but its axial (or, pseudo-trace) mode as well. Specifically, we consider the mimetic field to be (i) coupled explicitly to the well-known Holst extension of the Riemann–Cartan action, and (ii) identified with the square of the associated Barbero–Immirzi field, presumably a pseudo-scalar. The conformal symmetry originally prevaling in the theory would still hold, as the associated Cartan transformations do not affect the torsion pseudo-trace, and hence the Holst term. Demanding the theory to preserve the spatial parity symmetry as well, we show a geometric unification of the cosmological dark sector, and the feasibility of a super-accelerating regime in the course of evolution of the universe. From the observational perspective, assuming the cosmological evolution profile to be very close to that for $$\varLambda $$ Λ CDM, we further illustrate a smooth crossing of the so-called phantom barrier at a low red-shift, albeit with a restricted parametric domain. Subsequently, we determine the extent of the super-acceleration by examining the evolution of the relevant torsion parameters.

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R+S2 theories of gravity without big-bang singularity

Cited by 5 publications

References 20 publications

Einstein-Cartan wormhole solutions

Einstein-Cartan wormhole solutions

Dynamic wormhole solutions in Einstein-Cartan gravity

Mimetic-metric-torsion with induced axial mode and phantom barrier crossing

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