Lovelock Galileons and black holes

Charmousis, Christos; Tsoukalas, Minas

doi:10.1103/physrevd.92.104050

Cited by 28 publications

(33 citation statements)

References 114 publications

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“…Consequently, there have been several approaches to modify the structure of the gravitational action. Among the various proposals the most prominent ones include, e.g., f (R) gravity [28][29][30][31][32][33], Lovelock theories [34][35][36][37][38][39][40], scalar-tensor theories/Horndeski models [41][42][43][44][45][46][47][48][49][50] and theories with extra spatial dimensions [51][52][53][54][55][56][57][58][59][60][61][62] (see also [63]).…”

Section: Introductionmentioning

confidence: 99%

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

2019

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Continuum spectrum emitted by the accretion disk around quasars hold a wealth of information regarding the strong gravitational field produced by the massive central object. Such strong gravity regime is often expected to exhibit deviations from general relativity (GR) which may manifest through the presence of extra dimensions. Higher dimensions, which serve as the corner stone for string theory and M-theory can act as promising alternatives to dark matter and dark energy with interesting implications in inflationary cosmology, gravitational waves and collider physics. Therefore it is instructive to investigate the effect of more than four spacetime dimensions on the black hole continuum spectrum which provide an effective astrophysical probe to the strong gravity regime. To explore such a scenario, we compute the optical luminosity emitted by a thin accretion disk around a rotating supermassive black hole albeit in the presence of extra dimensions. The background metric resembles the Kerr-Newmann spacetime in GR where the tidal charge parameter inherited from extra dimensions can also assume negative signature. The theoretical luminosity computed in such a background is contrasted with optical observations of eighty quasars. The difference between the theoretical and observed luminosity for these quasars is used to infer the most favoured choice of the rotation parameter for each quasar and the tidal charge parameter. This has been achieved by minimizing/maximizing several error estimators, e.g., χ 2 , Nash-Sutcliffe efficiency, index of agreement etc. Intriguingly, all of them favour a negative value for the tidal charge parameter, a characteristic signature of extra dimensions. Thus accretion disk does provide a significant possibility of exploring the existence of extra dimensions through its close correspondence with the strong gravity regime.

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Section: Introductionmentioning

confidence: 99%

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

2019

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“…Among the various alternative theories there exist broadly three classifications: (a) The gravitational Lagrangian is modified by introduction of higher curvature terms, e.g., Lanczos-Lovelock gravity, f (R) gravity etc. The Lanczos-Lovelock theory is inherently ghost free, leading to second order field equations, while f (R) gravity models have ghost modes unless some specific conditions are being satisfied (see e.g., [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]); (b) Modified gravitational dynamics due to existence of extra dimensions, e.g., bulk Weyl tensor contributes additional terms to the effective lower dimensional gravitational field equations [26][27][28][29][30][31][32][33][34][35][36][37] and, finally (c) Scalar-tensor theories of gravity, which was first introduced as the Brans-Dicke theory and emerged in recent times in a more general context as Horndeski theories [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]…”

Section: Introductionmentioning

confidence: 99%

Excavating black hole continuum spectrum: Possible signatures of scalar hairs and of higher dimensions

Banerjee¹,

Chakraborty²,

SenGupta³

2017

Phys. Rev. D

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Continuum spectrum from black hole accretion disc holds enormous information regarding the strong gravity regime around the black hole and hence about the nature of gravitational interaction in extreme situations. Since in such strong gravity regime the dynamics of gravity should be modified from the Einstein-Hilbert one, its effect should be imprinted on the continuum spectrum originating from the black hole accretion. To explore the effects of these alternative theories on the black hole continuum spectrum in an explicit manner, we have discussed three alternative gravitational models having their origin in three distinct paradigms -(a) higher dimensions, (b) higher curvature gravity and (c) generalised Horndeski theories. All of them can have signatures sculptured on the black hole continuum spectrum, distinct from the standard general relativistic scenario. Interestingly all these models exhibit black hole solutions with tidal charge parameter which in these alternative gravity scenarios can become negative, in sharp contrast with the Reissner-Nordström black hole. Using the observational data of optical luminosity for eighty Palomer Green quasars we have illustrated that the difference between the theoretical estimates and the observational results gets minimized for negative values of the tidal charge parameter. As a quantitative estimate of this result we concentrate on several error estimators, including reduced χ 2 , Nash-Sutcliffe efficiency, index of agreement etc. Remarkably, all of them indicates a negative value of the tidal charge parameter, signaling the possibility of higher dimensions as well as scalar charge at play in those high gravity regimes.

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“…In the rest of the paper, we call such a theory the Lovelock-Galileon theory. It turns out that the field equations both for the metric and the scalar field are of second order [16].…”

Section: Introductionmentioning

confidence: 99%

Universal instability of hairy black holes in Lovelock-Galileon theories inDdimensions

2016

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We analyze spherically symmetric black hole solutions with time-dependent scalar hair in a class of Lovelock-Galileon theories, which are the scalar-tensor theories with second-order field equations in arbitrary dimensions. We first show that known black hole solutions in five dimensions are always plagued by the ghost/gradient instability in the vicinity of the horizon. We then generalize such black hole solutions to higher dimensions and show that the same instability found in five dimensions appears universally in any number of dimensions.

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Lovelock Galileons and black holes

Cited by 28 publications

References 114 publications

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

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

Excavating black hole continuum spectrum: Possible signatures of scalar hairs and of higher dimensions

Universal instability of hairy black holes in Lovelock-Galileon theories inDdimensions

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