In quest of axionic hairs in quasars

Banerjee, Indrani; Mandal, Bhaswati; SenGupta, Soumitra

doi:10.1088/1475-7516/2018/03/039

Cited by 9 publications

(8 citation statements)

References 88 publications

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“…bending of light, perihilion precession of Mercury etc., reveal that such fields cause minuscle changes compared to general relativity and hence cannot be detected by the present level of precision in the solar system based tests [27]. A quest for such a field in the spectrum of quasars have surprisingly revealed that axions which violate the energy condition seems to be favored by astrophysical observations related to black hole accretion [28]. Incidentally, the observed spectrum of the same quasars seem to favor certain classes of alternate gravity theories, e.g., extra dimensions, Einstein Gauss-Bonnet gravity in higher dimensions, etc.…”

Section: Introductionmentioning

confidence: 94%

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: Introductionmentioning

confidence: 94%

Implications of axionic hair on shadow of M87*

Banerjee,

Sau,

SenGupta

2019

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“…As a consequence, only the z-component of the energy flux vector q α has a non-zero contribution to the stress-energy tensor. For a more elaborate description of the thin accretion disk model one is referred to [106][107][108].…”

Section: Case B: 2u + P =mentioning

confidence: 99%

Does black hole continuum spectrum signal f(R) gravity in higher dimensions?

2020

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Extra dimensions, which led to the foundation and inception of string theory, provide an elegant approach to force-unification. With bulk curvature as high as the Planck scale, higher curvature terms, namely f (R) gravity seems to be a natural addendum in the bulk action. These can not only pass the classic tests of general relativity but also serve as potential alternatives to dark matter and dark energy. With interesting implications in inflationary cosmology, gravitational waves and particle phenomenology it is worth exploring the impact of extra dimensions and higher curvature in black hole accretion. Various classes of black hole solutions have been derived which bear nontrivial imprints of these ultraviolet corrections to general relativity. This in turn gets engraved in the continuum spectrum emitted by the accretion disk around black holes. Since the near horizon regime of supermassive black holes manifest maximum curvature effects, we compare the theoretical estimates of disk luminosity with quasar optical data to discern the effect of the modified background on the spectrum. In particular, we explore a certain class of black hole solution bearing a striking resemblance with the well-known Reissner-Nordström de Sitter/anti-de Sitter/flat spacetime which unlike general relativity can also accommodate a negative charge parameter. By computing error estimators like chi-square, Nash-Sutcliffe efficiency, index of agreement, etc. we infer that optical observations of quasars favor a negative charge parameter which can be a possible indicator of extra dimensions. The analysis also supports an asymptotically de Sitter spacetime with an estimate of the magnitude of the cosmological constant whose origin is solely attributed to higher curvature terms in higher dimensions. * tpib@iacs.res.in † tpbm3@iacs.res.in ‡ tpssg@iacs.res.in arXiv:1905.12820v2 [gr-qc] 1 Aug 2019 is still elusive and ill-understood [15][16][17]. All this makes the quest for a more complete theory of gravity increasingly compelling such that it yields GR in the low energy limit. Consequently a surfeit of alternate gravity models are proposed which can potentially fulfill the deficiencies in GR. A viable alternate gravity theory must be free from ghost modes, be consistent with solar system based tests, should not engender a fifth force in local physics and should successfully explain observations that GR fails to address. The alternate gravity models which fulfill these benchmark can be broadly classified into three categories: (i) Modified gravity models where the gravity action is supplemented with higher curvature terms, e.g., f(R) gravity [18][19][20][21], Lanczos-Lovelock models etc. [22][23][24][25][26] (ii) Extra-dimensional models that alter the effective 4-dimensional gravitational field equations due to the bulk Weyl stresses and higher order corrections to the stress-tensor [27][28][29][30][31][32][33] and (iii) Scalar-tensor theories of gravity which include the Brans-Dicke theory and the more general Horndeski models [34][35][36][...

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“…Thus owing to their simpler structure we will explore the observed QPOs in BHs to decipher the signatures of extra dimensions. In particular, our earlier works [60,[71][72][73] have consistently suggested the possibility of a negative tidal charge parameter through various BH observations. This has further motivated us to observe if a similar conclusion regarding the tidal charge holds true for the QPOs as well, which will enable us to understand if such an observation is consistent with our previous findings.…”

Section: Introductionmentioning

confidence: 64%

Looking for extra dimensions in the observed quasi-periodic oscillations of black holes

Banerjee,

Chakraborty,

SenGupta

2021

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Quasi-periodic oscillations, often present in the power density spectrum of accretion disk around black holes, are useful probes for the understanding of gravitational interaction in the near-horizon regime of black holes. Since the presence of an extra spatial dimension modifies the near horizon geometry of black holes, it is expected that the study of these quasi-periodic oscillations may shed some light on the possible existence of these extra dimensions. Intriguingly, most of the extra dimensional models, which are of significant interest to the scientific community, predicts the existence of a tidal charge parameter in black hole spacetimes. This tidal charge parameter can have an overall negative sign and is a distinctive signature of the extra dimensions. Motivated by this, we have studied the quasi-periodic oscillations for a rotating braneworld black hole using the available theoretical models. Subsequently, we have used the observations of the quasi-periodic oscillations from available black hole sources, e.g., GRO J1655 -40, XTE J1550 -564, GRS 1915 + 105, H 1743 + 322 and Sgr A* and have compared them with the predictions from the relevant theoretical models, in order to estimate the tidal charge parameter. It turns out that among the 11 theoretical models considered here, 8 of them predict a negative value for the tidal charge parameter, while for the others negative values of the tidal charge parameter are also well within the 1-σ confidence interval.

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In quest of axionic hairs in quasars

Cited by 9 publications

References 88 publications

Implications of axionic hair on shadow of M87*

Implications of axionic hair on shadow of M87*

Does black hole continuum spectrum signal f(R) gravity in higher dimensions?

Looking for extra dimensions in the observed quasi-periodic oscillations of black holes

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