The Palatini Approach Beyond Einstein’s Gravity

Olmo, Gonzalo J.

doi:10.1007/978-3-319-00297-2_14

Cited by 6 publications

(8 citation statements)

References 22 publications

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“…inside the throat), let us consider the geodesic motion of point-like particles. The geodesics for general static, spherically symmetric geometries with line element ds 2 = −C(y)dt 2 + B −1 (y)dy 2 + r 2 (y)dΩ 2 , are described by the equation (see [40] for details)…”

Section: α >mentioning

confidence: 99%

New scalar compact objects in Ricci-based gravity theories

Afonso

Olmo

Orazi

et al. 2019

J. Cosmol. Astropart. Phys.

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Taking advantage of a previously developed method, which allows to map solutions of General Relativity into a broad family of theories of gravity based on the Ricci tensor (Ricci-based gravities), we find new exact analytical scalar field solutions by mapping the free-field static, spherically symmetric solution of General Relativity (GR) into quadratic f (R) gravity and the Eddingtoninspired Born-Infeld gravity. The obtained solutions have some distinctive feature below the wouldbe Schwarzschild radius of a configuration with the same mass, though in this case no horizon is present. The compact objects found include wormholes, compact balls, shells of energy with no interior, and a new kind of object which acts as a kind of wormhole membrane. The latter object has Euclidean topology but connects antipodal points of its surface by transferring particles and null rays across its interior in virtually zero affine time. We point out the relevance of these results regarding the existence of compact scalar field objects beyond General Relativity that may effectively act as black hole mimickers. *

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Section: α >mentioning

confidence: 99%

New scalar compact objects in Ricci-based gravity theories

Afonso

Olmo

Orazi

et al. 2019

J. Cosmol. Astropart. Phys.

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“…where λ is the affine parameter. Since in the action (1) defining our model, the matter part couples to the metric but not to the connection, we will focus on the geodesics associated to the physical metric g µν , which are the ones that the matter fields follow according to the Einstein equivalence principle (see [37] for an extended discussion on geodesics in metric-affine spaces). The analysis can be largely simplified by writing the geodesic equation using the tangent vector u µ = dx µ /dλ, which satisfies u µ u µ = k, with k = 1, 0, −1 corresponding to spacelike, null, and timelike geodesics, respectively.…”

Section: B Geodesic Completenessmentioning

confidence: 99%

What is a singular black hole beyond general relativity?

2017

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Exploring the characterization of singular black hole spacetimes, we study the relation between energy density, curvature invariants, and geodesic completeness using a quadratic f (R) gravity theory coupled to an anisotropic fluid. Working in a metric-affine approach, our models and solutions represent minimal extensions of General Relativity (GR) in the sense that they rapidly recover the usual Reissner-Nordström solution from near the inner horizon outwards. The anisotropic fluid helps modify only the innermost geometry. Depending on the values and signs of two parameters on the gravitational and matter sectors, a breakdown of the correlations between the finiteness/divergence of the energy density, the behavior of curvature invariants, and the (in)completeness of geodesics is obtained. We find a variety of configurations with and without wormholes, a case with a de Sitter interior, solutions that mimic non-linear models of electrodynamics coupled to GR, and configurations with up to four horizons. Our results raise questions regarding what infinities, if any, a quantum version of these theories should regularize.

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“…which is a second-order differential equation to be supplied with initial conditions x µ (0) and dx µ /du| 0 . The general formalism for geodesic motion in Palatini theories of gravity has been developed with certain detail in [39]. First thing to note is that the matter sector of our theory, as described by the energy-momentum tensor (12), is assumed to couple to the gravitational sector (2) only via the metric and the matter fields (and not via the connection).…”

Section: Geodesic Structurementioning

confidence: 99%

“…For null geodesics, u µ u µ = 0, this interpretation cannot be sustained, but the quotient L/E can be identified instead as an apparent impact parameter as seen from asymptotic infinity. After all these considerations, the geodesic equation for a geometry of the form (27) can be written as [39] 1…”

Section: Geodesic Structurementioning

confidence: 99%

Nonsingular black holes, wormholes, and de Sitter cores from anisotropic fluids

2017

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We study Born-Infeld gravity coupled to an anisotropic fluid in a static, spherically symmetric background. The free function characterizing the fluid is selected on the following grounds: i) recovery of the Reissner-Nordström solution of GR at large distances, ii) fulfillment of classical energy conditions and iii) inclusion of models of nonlinear electrodynamics as particular examples. Four branches of solutions are obtained, depending on the signs of two parameters on the gravity and matter sectors. On each branch, we discuss in detail the modifications on the innermost region of the corresponding solutions, which provides a plethora of configurations, including nonsingular black holes and naked objects, wormholes and de Sitter cores. The regular character of these configurations is discussed according to the completeness of geodesics and the behaviour of curvature scalars.

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The Palatini Approach Beyond Einstein’s Gravity

Cited by 6 publications

References 22 publications

New scalar compact objects in Ricci-based gravity theories

New scalar compact objects in Ricci-based gravity theories

What is a singular black hole beyond general relativity?

Nonsingular black holes, wormholes, and de Sitter cores from anisotropic fluids

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