Decoding signatures of extra dimensions and estimating spin of quasars from the continuum spectrum

Banerjee, Indrani; Chakraborty, Sumanta; SenGupta, Soumitra

doi:10.1103/physrevd.100.044045

Cited by 40 publications

(36 citation statements)

References 197 publications

(255 reference statements)

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“…In a previous work [99] we explored the sole impact of the charge parameter on the continuum spectrum of eighty quasars to infer that optical observations of quasars favor a negative charge parameter. This work is subsequently generalized to axi-symmetric spacetimes [136] where the metric resembles the familiar Kerr-Newmann solution in GR. Inclusion of black hole rotation not only corroborates our earlier finding but also enables us to estimate the spin of the quasars [136].…”

Section: Discussionmentioning

confidence: 99%

“…This work is subsequently generalized to axi-symmetric spacetimes [136] where the metric resembles the familiar Kerr-Newmann solution in GR. Inclusion of black hole rotation not only corroborates our earlier finding but also enables us to estimate the spin of the quasars [136]. This is further supported by the study of quasi-periodic oscillations in the black hole power spectrum where a negative charge parameter is reported to be favored by observations [137].…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

2020

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“…Possible constraints on extra dimensions from weak field tests of gravity [37], electromagnetic observations of quasars [38][39][40], collision of binary black holes and neutron stars [20][21][22][23] and calculation of quadrupole moment [41] have already been reported. In this paper we investigate the shadow of such braneworld black holes in light of the observed silhouette of M87* by the Event Horizon Telescope collaboration.…”

Section: Introductionmentioning

confidence: 99%

Silhouette of M87*: A new window to peek into the world of hidden dimensions

2020

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The recent observation of the shadow of the supermassive black hole M87*, located at the centre of the M87 galaxy, by the Event Horizon Telescope collaboration has opened up a new window to probe the strong gravity regime. In this paper, we explicitly demonstrate the consequences of this observation on brane world black hole, whose characteristic feature being existence of a negative tidal charge. Our results are based on three observables associated with the shadow of M87*, namely, deviation from circularity, axis ratio and angular diameter of the shadow. These explicitly demonstrate that the existence of a negative tidal charge parameter, marking a deviation from general relativity, is more favoured.

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“…Following this motivation, in this paper we consider models of rotating ECOs in the Braneworld scenario. In particular, we investigate the physics of the rotating ECOs living on the brane, having an exterior geometry described by the Kerr-Newman-like metric with the electric charge replaced by the 'tidal' charge parameter inherited from the bulk [44,45] (for other observational signatures of the tidal charge parameter, see [46][47][48][49]). Therefore, these rotating ECOs with a tidal charge and a reflective quantum membrane in the near horizon region can be conceived as a simplified model to capture the near horizon quantum gravity modifications.…”

Section: Introductionmentioning

confidence: 99%

Ergoregion instability and echoes for braneworld black holes: Scalar, electromagnetic and gravitational perturbations

Dey,

Biswas,

Chakraborty

2020

Preprint

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In the context of higher dimensional braneworld scenario, we have argued that the occurrence of horizonless exotic compact objects, as an alternative to classical black holes, are more natural. These exotic compact objects carry a distinctive signature of the higher dimension, namely a tidal charge parameter, inherited from the projection of the higher dimensional Weyl tensor onto the four dimensional spacetime we live in. Due to the absence of any horizon, rotating exotic compact objects are often unstable because of superradiance. Interestingly, these higher dimensional exotic compact objects, in the presence of the tidal charge, are more stable than their four dimensional counterpart. A similar inference is drawn by analysing the static modes associated with these exotic compact objects, irrespective of the nature of the perturbation i.e., it holds true for scalar, electromagnetic and also gravitational perturbation. The post-merger ringdown phase of the exotic compact object in the braneworld scenario, which can be described in terms of the quasi-normal modes, holds plethora of information regarding the nature of the higher dimension. In this connection we have discussed the analytical computation of the quasi-normal modes as well as their numerical estimation for perturbations of arbitrary spin, depicting existence of echoes in the ringdown waveform. As we have demonstrated, the echoes in the ringdown waveform depends explicitly on the tidal charge parameter and hence its future detection can provide constraints on the tidal charge parameter, which in turn will enable us to provide a possible bound on the length of the extra dimension.

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Decoding signatures of extra dimensions and estimating spin of quasars from the continuum spectrum

Cited by 40 publications

References 197 publications

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

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

Silhouette of M87*: A new window to peek into the world of hidden dimensions

Ergoregion instability and echoes for braneworld black holes: Scalar, electromagnetic and gravitational perturbations

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