Cosmic stringlike objects in hybrid metric-Palatini gravity

Harko, Tiberiu; Lobo, Francisco S. N.; da Silva, Hilberto M. R.

doi:10.48550/arxiv.2003.09751

Cited by 3 publications

(8 citation statements)

References 74 publications

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“…In particular, it agrees with the classical tests in the Solar system [10], fairly well solves the DM problem concerning the dynamics of galaxies and galaxy clusters; it has been shown to be able to describe an accelerating Universe without invoking a cosmological constant [11]. Some papers have been devoted to the possible existence and properties of vacuum static, spherically symmetric black holes and wormholes in HMPD [12][13][14] as well as static cylindrically symmetric configurations intended to reproduce the basic properties of cosmic strings [15].…”

Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

“…The same objective was formulated in [15], where the authors used the coordinate condition α = γ in our notations (that is, g tt = −g xx , see Eq. ( 17) in [15], and note that there the radial coordinate is denoted r instead of our x). In addition, based on the desired string interpretation, it was postulated there that the metric should be invariant under boosts in the z direction [20], which leads to the requirement g tt = −g zz .…”

Section: Introductionmentioning

confidence: 99%

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Hybrid metric-Palatini gravity: Regular stringlike configurations

Бронников¹,

Bolokhov²,

Skvortsova³

2020

Preprint

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We discuss static, cylindrically symmetric vacuum solutions of hybrid metric-Palatini gravity (HMPG), a recently proposed theory that has been shown to successfully pass the local observational tests and to produce a certain progress in cosmology. We use HMPG in its well-known scalar-tensor representation. The latter coincides with general relativity containing, as a source of gravity, a conformally coupled scalar field φ and a self-interaction potential V (φ) . The φ field can be canonical or phantom, and accordingly the theory splits into canonical and phantom sectors. We seek solitonic (stringlike) vacuum solutions of HMPG, that is, completely regular solutions with Minkowski metric far from the symmetry axis, with a possible angular deficit. A transition of the theory to the Einstein conformal frame is used as a tool, and many of the results apply to the general Bergmann-Wagoner-Nordtvedt class of scalar-tensor theories as well as f (R) theories of gravity. One of these results is a one-to-one correspondence between stringlike solution in the Einstein and Jordan frames if the conformal factor that connects them is everywhere regular. An algorithm for construction of stringlike solutions in HMPG and scalar-tensor theories is suggested, and some examples of such solutions are obtained and discussed.

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Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hybrid metric-Palatini gravity: Regular stringlike configurations

Бронников¹,

Bolokhov²,

Skvortsova³

2020

Preprint

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“…In all the models we have considered W (r) is a monotonically increasing function of r, that diverges at infinity. For the numerical integration of the field equations we have chosen a nonzero value for W (0), W (0) = 0, since, at least for the considered cases, no numerical solution satisfying the condition W (0) = 0 exists (for a more detailed discussion on the existence of an axis or its regularity, refer to [51]). From the point of view of the sign of σ(r), we have obtained two classes of solutions, with σ(r) taking negative values, and positive values, respectively.…”

Section: Discussion and Final Remarksmentioning

confidence: 99%

“…String-type solutions have also been studied in the framework of modified theories of gravity, such as in Brans-Dicke theory [38], general scalar-tensor theories [38][39][40][41][42][43][44][45][46][47][48], f (R, L m ) gravity [49,50], and hybrid metric-Palatini gravity (HMPG) [51]. In this work, we generalize the previous analysis and consider cosmic string-like objects in the generalized HMPG theory [52], which is described by an action depending on a general function of both the metric Ricci scalar R and the Palatini Ricci scalar R written in terms of an independent connection Γc ab , thus adding an extra degree of freedom to the non-generalized hybrid metric-Palatini gravity on which the action is constructed from the Einstein-Hilbert action via the addition of an arbitrary function of R only.…”

Section: E Cosmic String-like Objects In Modified Theories Of Gravitymentioning

confidence: 99%

Cosmic strings in generalized hybrid metric-Palatini gravity

da Silva,

Harko,

Lobo

et al. 2021

Preprint

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We consider the possible existence of gravitationally bound stringlike objects in the framework of the generalized hybrid metric-Palatini gravity theory, in which the gravitational action is represented by an arbitrary function of the Ricci and of the Palatini scalars, respectively. The theory admits an equivalent scalar-tensor representation in terms of two independent scalar fields. Assuming cylindrical symmetry, and the boost invariance of the metric, we obtain the gravitational field equations that describe cosmic stringlike structures in the theory. The physical and geometrical properties of the cosmic strings are determined by the two scalar fields, as well by an effective field potential, functionally dependent on both scalar fields. The field equations can be exactly solved for a vanishing, and a constant potential, respectively, with the corresponding string tension taking both negative and positive values. Furthermore, for more general classes of potentials, having an additive and a multiplicative algebraic structure in the two scalar fields, the gravitational field equations are solved numerically. For each potential we investigate the effects of the variations of the potential parameters and of the boundary conditions on the structure of the cosmic string. In this way, we obtain a large class of stable stringlike astrophysical configurations, whose basic parameters (string tension and radius) depend essentially on the effective field potential, and on the boundary conditions.

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Beyond Einstein's General Relativity: Hybrid metric-Palatini gravity and curvature-matter couplings

Harko,

Lobo

2020

Preprint

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A. Going beyond Einstein's General Relativity B. Motivations for hybrid metric-Palatini gravity C. Couplings between geometry and matter D. Outline of article II Hybrid metric-Palatini gravity I. General formalism A. Action and field equations B. The Newtonian limit C. The Post-Newtonian limit D. f (X) representation II. Cosmological applications A. The generalized Friedmann equations, and the deceleration parameter B. Alternative form of the generalized Friedmann equations C. Specific FLRW cosmological models 1. de Sitter type solutions 2. Marginally accelerating solutions 3. Accelerating solutions of the field equations D. Einstein's static Universe E. Gödel type solutions F. Dynamical system analysis G. Cosmological perturbations 1. Perturbations in the matter dominated cosmology 2. Perturbation propagations in the vacuum H. Constraining the cosmological evolution III. Galactic and extragalactic dynamics A. Galactic rotation curves B. Clusters of galaxies IV. Stellar type objects, black holes and wormholes 1. Stars and black holes 2. Wormhole solutions V. Thermodynamics, branes, screening, gravitational waves, strings, and further work VI. Beyond the standard linear hybrid metric-Palatini theory III Curvature-matter couplings VII. Linear nonminimal curvature-matter couplings actions and gravitational field equations A. Scalar field-geometry couplings B. Theories with standard curvature-geometry coupling C. Scalar-tensor representation D. Generalized f (R, L m) curvature-matter couplings VIII. f (R, T ) gravity A. Action and gravitational field equations B. The equations of motion of test particles C. Specific cosmological solution IX. f (R, T, R µν T µν ) gravity A. Action and field equations of the f (R, T, R µν T µν ) gravity B. Equation of motion of massive test particles C. The Dolgov-Kawasaki instability in f (R, T, R µν T µν ) gravity D. Specific cosmological application X. Irreversible matter creation processes through a nonminimal curvature-matter coupling A. Thermodynamic open systems B. Thermodynamic interpretation in curvature-matter couplings XI. Quantum cosmology of f (R, T ) curvature-matter couplings A. The Wheeler-de Witt equation in f (R, T ) gravity 1. The effective cosmological Lagrangian and the potential 2. The cosmological Hamiltonian 3. The Wheeler-de Witt equation B. Specific cosmological application: f (R, T ) = F 0 (R) + θRT 1. The Hamiltonian and the Wheeler-de Witt equation 2. The Hamiltonian form of the field equations C. The problem of time D. The physical interpretation of the effective Hamiltonian IV Conclusions

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Cosmic stringlike objects in hybrid metric-Palatini gravity

Cited by 3 publications

References 74 publications

Hybrid metric-Palatini gravity: Regular stringlike configurations

Hybrid metric-Palatini gravity: Regular stringlike configurations

Cosmic strings in generalized hybrid metric-Palatini gravity

Beyond Einstein's General Relativity: Hybrid metric-Palatini gravity and curvature-matter couplings

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