Quadratic gravity and conformally coupled scalar fields

Cáceres, Nicolás; Figueroa, José; Oliva, Julio; Oyarzo, Marcelo; Stuardo, Ricardo

doi:10.1007/jhep04(2020)157

Cited by 15 publications

(10 citation statements)

References 54 publications

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“…BH solutions within this theory have been obtained by Astorino [289] (see also Refs. [290][291][292][293][294][295][296][297] for BH and black brane solutions within related models), and contain a hair parameter S which is related to the scalar field pro-file (and is directly connected to the value of the scalar field at the horizon). The hair parameter, or scalar charge, emerges as an integration constant and describes primary hair, i.e.…”

Section: Morris-thorne Traversable Wormholementioning

confidence: 99%

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

Vagnozzi¹,

Roy²,

Tsai³

et al. 2022

Preprint

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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, allowing us to test whether the Kerr metric provides a good description of the space-time in the vicinity of the event horizons of supermassive BHs. We consider a wide range of well-motivated deviations from classical General Relativity solutions, and constrain them using the Event Horizon Telescope (EHT) observations of Sagittarius A * (SgrA * ), connecting the size of the bright ring of emission to that of the underlying BH shadow and exploiting high-precision measurements of SgrA * 's mass-to-distance ratio. The scenarios we consider, and whose fundamental parameters we constrain, include various regular BH models, string-and non-linear electrodynamics-inspired space-times, scalar field-driven violations of the no-hair theorem, alternative theories of gravity, new ingredients such as the generalized uncertainty principle and Barrow entropy, and BH mimickers including examples of wormholes and naked singularities. We demonstrate that SgrA * 's image places particularly stringent constraints on models predicting a shadow size which is larger than that of a Schwarzschild BH of a given mass: for instance, in the case of Barrow entropy we derive constraints which are significantly tighter than the cosmological ones. Our results are among the first tests of fundamental physics from the shadow of SgrA * and, while the latter appears to be in excellent agreement with the predictions of General Relativity, we have shown that various well-motivated alternative scenarios (including BH mimickers) are far from being ruled out at present.

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Section: Morris-thorne Traversable Wormholementioning

confidence: 99%

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

Vagnozzi¹,

Roy²,

Tsai³

et al. 2022

Preprint

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show abstract

“…The integrability properties of these models have been well-studied since then, providing solutions for spacetimes with acceleration [41,42], NUT charge [43], rotation [44] and a full analysis of conformally coupled black holes in the entire Plebański-Demiański family [45,46]. Moreover, several solutions have been found also in the presence of external magnetic fields [47,48] and in theories with higher order corrections [49] and .…”

Section: Introductionmentioning

confidence: 99%

(A)dS Taub-NUT and exact black bounces with scalar hair

Barrientos¹,

Cisterna²,

Mora³

et al. 2022

Preprint

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We present a new family of exact four-dimensional Taub-NUT spacetimes in Einstein-Λ theory supplemented with a conformally coupled scalar field exhibiting a power-counting superrenormalizable potential. Our configurations are constructed in the following manner: A solution of a conformally coupled theory with a conformal potential, henceforth the seed (gµν , φ), is transformed by the action of a specific change of frame in addition with a simultaneous shift of the seed scalar field. The conformal factor of the transformation and the shift are both affine functions of the original scalar φ. The new configuration, (ḡµν , φ), solves the field equations of a conformally coupled theory with the extended aforementioned super-renormalizable potential, this under the presence of an effective cosmological constant. The new spectrum of solutions is notoriously enhanced with respect to the original seed containing regular black holes, wormholes, and bouncing cosmologies. We highlight the existence of two types of exact black bounces given by de Sitter and anti-de Sitter geometries that transit across three different configurations each. The de Sitter geometries transit from a regular black hole with event and cosmological horizons to a bouncing cosmology that connects two de Sitter Universes with different values of the asymptotic cosmological constant. An intermediate phase, which might be represented by two different configurations, takes place. These configurations are given by a de Sitter wormhole or by a bouncing cosmology that connects two de Sitter Universes, both under the presence of a cosmological horizon. On the other hand, the anti-de Sitter geometries transit from a regular black hole with inner and event horizons to a wormhole that connects two asymptotic boundaries with different constant curvatures. The intermediate phase is given in this case by an anti-de Sitter regular black hole with a single event horizon. This regular black hole might appear in two different configurations. As a regular anti-de Sitter black hole inside of an anti-de Sitter wormhole or as an anti-de Sitter regular black hole with a cosmological bounce in its interior. All these geometries are shown to be smoothly connected by the mass parameter only. Other standard stationary black holes, bouncing cosmologies and wormholes are also identified.

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“…Scalar-tensor theories have provided a rich reservoir of hairy black hole solutions, systematically circumventing no-hair theorems by means of different approaches [70]. The archetypical model is given by Einstein gravity supplemented by conformally coupled scalar fields for which several black hole solutions, beyond spherical symmetry, have been found [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]. Even in the case of gravitational instantons, where only few numerical gravitational instantons with nontrivial scalar field are known [87,88], this model proved itself fruitful providing a remarkable exception of an analytic gravitational instanton [77,89].…”

Section: Introductionmentioning

confidence: 99%

Gravitational instantons with conformally coupled scalar fields

Barrientos,

Cisterna,

Corral

et al. 2022

Preprint

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We present novel regular Euclidean solutions to General Relativity in presence of Maxwell and conformally coupled scalar fields. In particular, we consider metrics of the Eguchi-Hanson and Taub-NUT families to solve the field equations analytically. The solutions have nontrivial topology labeled by the Hirzebruch signature and Euler characteristic that we compute explicitly. We find that, although the solutions are locally inequivalent with the original (anti-)self-dual Eguchi-Hanson metric, their asymptotically locally Euclidean limit leads to the same global properties.We revisit the Taub-NUT solution previously found in the literature, analyze their nuts and bolts structure, and obtain the renormalized Euclidean on-shell action as well as their topological invariants. Additionally, we discuss how the solutions get modified in presence of higher-curvature corrections that respect conformal invariance. In the conformally invariant case, we obtain novel Eguchi-Hanson and Taub-NUT solutions and demonstrate that both Euclidean on-shell action and Noether-Wald charges are finite without any reference to intrinsic boundary counterterms.

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Quadratic gravity and conformally coupled scalar fields

Cited by 15 publications

References 54 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$^*$

(A)dS Taub-NUT and exact black bounces with scalar hair

Gravitational instantons with conformally coupled scalar fields

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