Dynamical suppression of spacetime torsion

Paul, Tanmoy; SenGupta, Soumitra

doi:10.1140/epjc/s10052-019-7109-5

Cited by 13 publications

(9 citation statements)

References 54 publications

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“…Moreover, the suppression of field has been discussed in several physical scenarios, e.g. in the context of warped brane-world models [60] with bulk Kalb-Ramond fields [61,62] and the related stabilization of the modulus [63], in the context of higher curvature gravity where the associated scalar degrees of freedom diminishes the coupling of such a field with the Standard Model fermions [64, and in the inflationary era induced by higher curvature gravity [66,67] and higher dimensions [68].…”

Section: Discussionmentioning

confidence: 99%

Implications of axionic hair on shadow of M87*

Banerjee,

Sau,

SenGupta

2019

Preprint

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Detection of axion field can unfold intriguing facets of our universe in several astrophysical and cosmological scenarios. In four dimensions, such a field owes its origin to the completely anti-symmetric Kalb-Ramond field strength tensor. Its invisibility in the solar system based tests compels one to look for its signatures in the strong field regime. The recent observation of the shadow of the supermassive black hole in the galaxy M87 ushers in a new opportunity to test for the footprints of axion in the near horizon region of black holes, where the gravity is expected to be strong. In this paper, we explore the impact of axion on the black hole shadow and compare the result with the available image of M87*. Our analysis indicates that axion which violates the energy condition seems to be favored by observations. The implications are discussed.

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Section: Discussionmentioning

confidence: 99%

Implications of axionic hair on shadow of M87*

Banerjee,

Sau,

SenGupta

2019

Preprint

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“…The demonstration goes as follows: its equation of state (EoS) parameter is unity, and the conservation equation of the KR field is given by _ ρ KR þ 6Hρ KR ¼ 0, solving which one obtains ρ KR ∝ 1=a 6 ; i.e., the energy density of the KR field decreases with faster rate in comparison to pressureless matter and radiation. (The negligible footprint of the KR field in the present Universe can also be described from the higher dimensional point of view [81] where the KR field is generally considered to be a bulk field and our four-dimensional visible Universe is a brane embedded within the higher dimensional spacetime; further a nondynamical approach is also presented in [82] to explain the imperceptible signatures of the KR field in our Universe.) Thereby, it clearly depicts that the present Universe may be free from the direct signatures of the KR field; however, the KR field has considerable effects during the early Universe (when the scale factor is small compared to the present one).…”

Section: A Holographic Cutoff For Fðrþ Inflationary Modelsmentioning

confidence: 92%

Unifying holographic inflation with holographic dark energy: A covariant approach

et al. 2020

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In the present paper, we use the holographic approach to describe the early-time acceleration and the late-time acceleration eras of our Universe in a unified manner. Such "holographic unification" is found to have a correspondence with various higher curvature cosmological models with or without matter fields. The corresponding holographic cutoffs are determined in terms of the particle horizon and its derivatives, or the future horizon and its derivatives. As a result, the holographic energy density we propose is able to merge various cosmological epochs of the Universe from a holographic point of view. We find the holographic correspondence of several FðRÞ gravity models, including axion-FðRÞ gravity models, of several Gauss-Bonnet FðGÞ models and finally of FðTÞ models, and in each case we demonstrate that it is possible to describe in a unified way inflation and late-time acceleration in the context of the same holographic model.

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“…This in turn indicates a negligible field strength for axion whose suppression has been observed in several other physical scenarios, e.g. in the inflationary era induced by higher curvature gravity [102,103] and higher dimensions [104], in the warped braneworld scenario [105] with bulk Kalb-Ramond fields [106,107] and the related stabilization of the modulus [108] and so on. We further point out that our results are in agreement with a previous work [77] where such a conclusion has been independently arrived by investigating the observed jet power and the radiative efficiencies of the microquasars with the corresponding theoretical estimates in the Kerr-Sen background.…”

Section: Summary and Concluding Remarksmentioning

confidence: 75%

Implications of Einstein-Maxwell dilaton-axion gravity from the black hole continuum spectrum

Banerjee,

Mandal,

SenGupta

2020

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String inspired models can serve as potential candidates to replace general relativity (GR) in the high energy/high curvature regime where quantum gravity is expected to play a vital role. Such models not only subsume the ultraviolet nature of gravity but also exhibit promising prospects in resolving issues like dark matter and dark energy, which cannot be adequately addressed within the framework of GR. The Einstein-Maxwell dilaton-axion (EMDA) theory, which is central to this work is one such string inspired model arising in the low energy effective action of the heterotic string theory with interesting implications in inflationary cosmology and in the late time acceleration of the universe. It is therefore important to survey the role of such a theory in explaining astrophysical observations, e.g. the continuum spectrum of black holes which are expected to hold a wealth of information regarding the background metric. The Kerr-Sen spacetime corresponds to the exact, stationary and axi-symmetric black hole solution in EMDA gravity, possessing dilatonic charge and angular momentum originating from the axionic field. In this work, we compute the theoretical spectrum from the accretion disk around quasars in the Kerr-Sen background assuming the thin accretion disk model due to Novikov & Thorne. This is then used to evaluate the theoretical estimates of optical luminosity for a sample of eighty Palomar-Green quasars which are subsequently compared with the available observations. Our analysis based on error estimators like the χ 2 , the Nash-Sutcliffe efficiency, the index of agreement etc., indicates that black holes carrying non-existent or weak dilaton charges (viz, 0 r2 0.1) are observationally more favored. The spins associated with the quasars are also estimated. Interestingly, a similar conclusion has been independently achieved by studying the observed jet power and the radiative efficiencies of microquasars. The implications are discussed.

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Dynamical suppression of spacetime torsion

Cited by 13 publications

References 54 publications

Implications of axionic hair on shadow of M87*

Implications of axionic hair on shadow of M87*

Unifying holographic inflation with holographic dark energy: A covariant approach

Implications of Einstein-Maxwell dilaton-axion gravity from the black hole continuum spectrum

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