Topological solutions in ungauged supergravity

Cruz-Dombriz, Álvaro de la; Shahbazi, C. S.

doi:10.1103/physrevd.89.065005

Cited by 8 publications

(16 citation statements)

References 56 publications

(84 reference statements)

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“…These constraints are satisfied if n = 1 + δ with δ ≥ 0. In spite of the experimental bounds on the exponent n, R n gravity has been the focus of much work aiming at exploring the possible phenomenology of f (R) gravity and many phase space analyses for R n cosmology are available in the literature [91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109] (see [113] for a phase space picture of general f (R) cosmology analogous to that of the previous section). Moreover, in strong curvature regimes in the early universe, in which the present-day Solar System constraints do not apply, Starobinsky-like inflation [114] corresponding to f (R) = R + µR 2 is well approximated by f (R) ≃ µR 2 .…”

Section: A Phase Space Interpretationmentioning

confidence: 99%

Perfect fluid solutions of Brans–Dicke andf(R)cosmology

Çiftci

Faraoni

2018

Annals of Physics

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Section: A Phase Space Interpretationmentioning

confidence: 99%

Perfect fluid solutions of Brans–Dicke andf(R)cosmology

Çiftci

Faraoni

2018

Annals of Physics

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“…In contradistinction for regular geometry with an interior wormhole spacetime, r 0 ≤ r ≤ R, and a Schwarzschildlike vacuum, r h < R ≤ r < ∞, at a junction interface. In addition, the junction conditions in this theory have been worked out [86].…”

Section: V1 Field Equations With Conformal Symmetry In Teleparallelmentioning

confidence: 99%

Conformally symmetric traversable wormholes in modified teleparallel gravity

et al. 2020

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In this paper, we consider wormhole geometries in the context of teleparallel equivalent of general relativity (TEGR) as well as f (T ) gravity. The TEGR is an alternative geometrical formulation of Einstein's general relativity, where modified teleparallel gravity or f (T ) gravity has been invoked as an alternative approach for explaining an accelerated expansion of the universe. We present the analytical solutions under the assumption of spherical symmetry and the existence of a conformal Killing vectors to proceed a more systematic approach in searching for exact wormhole solutions. More preciously, the existence of a conformal symmetry places restrictions on the model. Considering the field equations with a diagonal tetrad and anisotropic distribution of the fluid, we study the properties of traversable wormholes in TEGR that violates the weak and the null energy conditions at the throat and its vicinity. In the second part, wormhole solutions are constructed in the framework of f (T ) gravity, where T represents torsion scalar. As a consistency check, we also discuss the behavior of energy conditions with a viable power-law f (T ) model and the corresponding shape functions. In addition, a wide variety of solutions are deduced by considering a linear equation of state relating the density and pressure, for the isotropic and anisotropic pressure, independently of the shape functions, and various phantom wormhole geometries are explored.

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“…Probing properties of the dark energy is important, and it has been studied in the standard cosmology or the several modified gravity theories [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75]. Next we investigate the properties of geometrical dark energy in this GBD theory, and analyze the effects of the BD scalar field.…”

Section: Effective State Parameter Of Geometrical Dark Energy In mentioning

confidence: 99%

“…Studies on the modified gravity theories of GR have been always the hot area. Several modified gravity theories have been widely studied [1][2][3][4][5][6], especially two simple modifications to GR: the f (R) theory [7,8] and the Brans-Dicke (BD) theory [9].…”

Section: Introductionmentioning

confidence: 99%

The generalized Brans-Dicke theory and its cosmology

Yang

et al. 2019

Eur. Phys. J. Plus

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A generalized Brans-Dicke (GBD) theory is studied in this paper. The GBD theory is obtained by generalizing the Ricci scalar R to an arbitrary function f (R) in the original Brans-Dicke (BD) action.The interesting property has been found in the GBD theory, for example it can naturally solve the problem of γ value emerging in f (R) modified gravity (i.e. the inconsistent problem between the observational γ value and the theoretical γ value), without introducing the so-called chameleon mechanism. In this paper, we derive the cosmological equations and study the cosmology in the GBD theory. The cosmological solutions show that the GBD model can pass through the test of the observations, such as the observational Hubble data. Comparing with other theories, it can be found that the GBD theory have some other interesting properties or solve some problems existing in other theories. (1) It is well known that the f (R) theory are equivalent to the BD theory with a potential (abbreviated as BDV) for taking a specific value of the BD parameter ω = 0, where the specific choice: ω = 0 for the BD parameter is quite exceptional, and it is hard to understand the corresponding absence of the kinetic term for the field. However, for the GBD theory, it is similar to the double scalar-fields model, and both fields in the GBD own the non-disappeared dynamical effect.(2) One knows that in the double scalar-fields quintom model, it is required to include both the canonical quintessence field and the non-canonical phantom field in order to make the state parameter to cross over w = −1, while several fundamental problems are associated with phantom field, such as the problem of negative kinetic term and the fine-tuning problem, etc. While, in the GBD model, the state parameter of geometrical dark energy can cross over the phantom boundary w = −1 as achieved in the quintom model, without bearing the problems existing in the quintom model. (3) The GBD theory tends to investigate the physics from the viewpoint of geometry, while the BDV or the two scalar-fields quintom model tends to solve physical problems from the viewpoint of matter. It is possible that several special characteristics of scalar fields could be revealed through studies of geometrical gravity in the GBD. As an example, we investigate the potential V (φ) of the BD scalar field, and an effective form of V (φ) could be given by studying on the GBD theory. And, it seems that a viable condition for the BD theory could be found, i.e. the BD parameter should be ω > 0 for f > 0, if we assume that the effective form of the BD potential can be approximately written as a popular square function of φ.

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Topological solutions in ungauged supergravity

Abstract: A new general class of solutions of ungauged four-dimensional supergravity, in one-to-one correspondence with spherically symmetric, static black-hole solutions and Lifshitz solutions with hyperscaling violation is studied. The causal structure of the space-time is then elucidated.

Cited by 8 publications

References 56 publications

Perfect fluid solutions of Brans–Dicke andf(R)cosmology

Perfect fluid solutions of Brans–Dicke andf(R)cosmology

Conformally symmetric traversable wormholes in modified teleparallel gravity

The generalized Brans-Dicke theory and its cosmology

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