Classical big-bounce cosmology: dynamical analysis of a homogeneous and irrotational Weyssenhoff fluid
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A dynamical analysis of an effective homogeneous and irrotational Weyssenhoff fluid in general relativity is performed using the 1 + 3 covariant approach that enables the dynamics of the fluid to be determined without assuming any particular form for the spacetime metric. The spin contributions to the field equations produce a bounce that averts an initial singularity, provided that the spin density exceeds the rate of shear. At later times, when the spin contribution can be neglected, a Weyssenhoff fluid reduces to a standard cosmological fluid in general relativity. Numerical solutions for the time evolution of the generalized scale factor R ( t ) in spatially curved models are presented, some of which exhibit eternal oscillatory behaviour without any singularities. In spatially flat models, analytical solutions for particular values of the equation-of-state parameter are derived. Although the scale factor of a Weyssenhoff fluid generically has a positive temporal curvature near a bounce (i.e. ), it requires unreasonable fine tuning of the equation-of-state parameter to produce a sufficiently extended period of inflation to fit the current observational data.
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The square of the spin density for a fluid consisting of fermions with no spin polarization is given by Equation (8).
“The square of the spin density for a fluid consisting of fermions with no spin polarization is given by (Nurgaliev & Ponomariev 1983;Gasperini 1986;Brechet et al. 2008”
From UNIVERSE IN A BLACK HOLE IN EINSTEIN–CARTAN GRAVITY (2016) · cites this paper as Brechet et al. 2008
Section 2.1, Eq. (6), defines the squared spin-density scalar, and Section 3.2, Eqs. (30)–(31), explains that random spin averaging can leave this squared quantity nonzero even when the average spin tensor vanishes. The copy does not specify a fluid of unpolarized fermions or establish the formula in the citing document’s Eq. (8), whose contents were not provided. The source paper’s own Eq. (8) concerns the stress-energy tensor, not a fermion-specific squared spin density. (LLM, conf=0.78)
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UNIVERSE IN A BLACK HOLE IN EINSTEIN–CARTAN GRAVITY
Popławski, N. (2016) · The Astrophysical Journal · doi:10.3847/0004-637x/832/2/96 · Cited by 91 · see citing works
- Authors
- Brechet, S. D., Hobson, M. P., & Lasenby, A. N.
- Affiliations
- University of Cambridge (GB)
- Venue
- Classical and Quantum Gravity
- Publisher
- IOP Publishing
- Published
- 2008-12-02
- Volume
- 25
- Issue
- 24
- Pages
- 245016
- ISSN
- 0264-9381 (ISSN-L)
- 1361-6382
- OpenAlex
- W2003105923
- Cited by
- 46
- References
- 0
- Citations by year
- 2026: 1 · 2025: 2 · 2024: 6 · 2023: 4 · 2021: 2 · 2020: 3 · 2019: 3 · 2018: 6 · 2017: 3 · 2016: 2 · 2015: 2 · 2014: 2 · 2013: 1 · 2012: 1
- FWCI
- 1.55
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Classical and Quantum Gravity (publishedVersion)
- arXiv (Cornell University) (submittedVersion)
- Infoscience (Ecole Polytechnique Fédérale de Lausanne) (submittedVersion)
- Infoscience (Ecole Polytechnique Fédérale de Lausanne) (submittedVersion, cc-by-nc-nd)
- arXiv (Cornell University)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
- Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Noncommutative and Quantum Gravity Theories
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Relativity and Gravitational Theory
- Keywords
- Weyssenhoff fluid, initial singularity avoidance, spin density, 1+3 covariant formalism, inflation (cosmology), equation of state parameter, analytical solution
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