Bianchi type I cosmology with a Kalb–Ramond background field

Maluf, R. V.; Neves, Juliano C. S.

doi:10.1140/epjc/s10052-022-10109-2

Cited by 12 publications

(4 citation statements)

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“…46 Inspired by the Standard Model Extension (an effective field theory containing all possible Lorentz breaking operators in addition to the Standard Model and GR Lagrangian terms [761][762][763]) and by heterotic string theory [760], considered a scenario where the Kalb-Ramond field acquires a non-vanishing vacuum expectation value (VEV) b µν (with b 2 = b µν b µν ), as well as a non-minimal coupling to the Ricci tensor with strength ξ 2 (for the full action of the theory, see [760]). The non-zero VEV spontaneously breaks Lorentz invariance, leading to a host of interesting observational signatures [764][765][766].…”

Section: Kalb-ramond Black Holementioning

confidence: 99%

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

Vagnozzi

Roy

Tsai

et al. 2023

Class. Quantum Grav.

210

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Horizon-scale images of black holes (BHs) and their shadows have opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. We consider a wide range of well-motivated deviations from classical General Relativity (GR) BH solutions, and constrain them using the Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), connecting the size of the bright ring of emission to that of the underlying BH shadow and exploiting high-precision measurements of Sgr A*’s mass-to-distance ratio. The scenarios we consider, and whose fundamental parameters we constrain, include various regular BHs, string-inspired space-times, violations of the no-hair theorem driven by additional fields, alternative theories of gravity, novel fundamental physics frameworks, and BH mimickers including well-motivated wormhole and naked singularity space-times. We demonstrate that the EHT image of Sgr A* places particularly stringent constraints on models predicting a shadow size larger than that of a Schwarzschild BH of a given mass, with the resulting limits in some cases surpassing cosmological ones. Our results are among the first tests of fundamental physics from the shadow of Sgr A* and, while the latter appears to be in excellent agreement with the predictions of GR, we have shown that a number of well-motivated alternative scenarios, including BH mimickers, are far from being ruled out at present.

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Section: Kalb-ramond Black Holementioning

confidence: 99%

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

Vagnozzi

Roy

Tsai

et al. 2023

Class. Quantum Grav.

210

View full text Add to dashboard Cite

show abstract

“…Here, µναβ is the well known Levi-Cevita symbol, which is for Minkowskian spacetime equal to unity if it's indices are an even permutation of (1234), equal to −1 if indices are odd permutation of (1234) and vanish if one of the indices repeat. For KB field, stress-energy-momentum tensor reads [50]:…”

Section: Minimally Coupled Massless Kalb-ramond Fieldmentioning

confidence: 99%

“…B µν where is the antisymmetric rank 2 tensor, namely the Kalb-Ramond field. For the KB field, we have a set of two EoMs expressed as follows [47][48][49]:…”

Section: Minimally Coupled Massless Kalb-ramond Fieldmentioning

confidence: 99%

Compact stars admitting Finch-Skea symmetry in the presence of various matter fields*

Sokoliuk¹,

Baransky²,

Sahoo³

2023

Chinese Phys. C

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In the present article authors investigate the anisotropic stellar solutions admitting Finch-Skea symmetry (viable and non-singular metric potentials) in the presence of some exotic matter fields, such as: Bose-Einstein Condensate (BEC) dark matter, Kalb-Ramond fully anisotropic rank-2 tensor field from the low-energy string theory effective action, gauge field imposing $U(1)$ symmetry. Interior spacetime is matched with both Schwarzchild and Reissner-N"ordstrom vacuum spacetimes for BEC, KB and gauge fields respectively. Further, we have studied energy conditions, Equation of State (EoS), radial derivatives of energy density and anisotropic pressures, Tolman-Oppenheimer-Volkoff equilibrium condition, relativistic adiabatic index, sound speed and surface redshift. Most of the aforementioned conditions were satisfied and therefore solutions derived in the current study lie in the physically acceptable regime.

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“…Apart from the massless representation of the Lorentz group, the KR field also arise as closed string mode [67], and are of considerable interest, in the context of String theory. Recently the possible roles of Kalb-Ramond field (coupled to Bianchi-I geometry) in the Lorentz symmetry violation has been studied in [68]. In the arena of higher dimensional braneworld scenario or in higher curvature gravity theory, it has been shown that the KR coupling (with other normal matter fields) gets highly suppressed over the usual gravity-matter coupling, which explains why the KR field has negligible footprints at the present universe [69][70][71].…”

Section: Introductionmentioning

confidence: 99%

Ekpyrotic bounce driven by Kalb-Ramond field

Paul¹,

SenGupta²

2022

Preprint

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We propose an ekpyrotic bounce scenario driven by a second rank antisymmetric Kalb-Ramond field, where the universe initially contracts through an ekpyrotic stage having a non-singular bouncing like behaviour, and consequently, it smoothly transits to an expanding phase. In particular, the KR field has an interaction with a scalaron field (coming from higher curvature d.o.f) by a linear coupling. The interaction energy density between the KR and the scalaron grows faster than a −6 (with a being the scale factor of the universe) during the contraction phase -which has negligible effects at the distant past, however as the universe continues to contract, this interaction energy density gradually grows and plays a significant role in violating the null energy condition or to trigger a non-singular bounce at a minimum value of the scale factor. The existence of the ekpyrotic phase justifies the resolution of the BKL instability, where the anisotropic energy density gets diluted compared to that of the bouncing agent. The bounce being symmetric and ekpyrotic, the energy density of the bouncing agent rapidly decreases after the bounce during the expanding phase of the universe, and consequently the standard Big-Bang cosmology gets recovered. In regard to the perturbation analysis, we find that the comoving Hubble radius diverges at the distant past, which leads to the generation era of the primordial perturbation modes at the deep contracting phase far away from the bounce. In effect, the curvature perturbation gets a blue tilted spectrum over the large scale modes -not consistent with the Planck data. To circumvent this problem, we propose an extended scenario where the ekpyrotic phase is preceded by a quasi-matter dominated pre-ekpyrotic phase, and re-investigate the perturbation power spectrum. As a result, the primordial curvature perturbation, at scales that cross the horizon during the pre-ekpyrotic stage, turns out to be nearly scale invariant that is indeed consistent with the recent Planck data.

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Bianchi type I cosmology with a Kalb–Ramond background field

Cited by 12 publications

References 50 publications

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

Compact stars admitting Finch-Skea symmetry in the presence of various matter fields*

Ekpyrotic bounce driven by Kalb-Ramond field

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