Observational manifestations of black holes in the Horndeski gravity model
- PDF / 310,676 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 51 Downloads / 192 Views
, PARTICLES, FIELDS, GRAVITATION, AND ASTROPHYSICS
Observational Manifestations of Black Holes in the Horndeski Gravity Model D. A. Tretyakova* Institute for Natural Sciences, Ural Federal University, pr. Lenina 51, Yekaterinburg, 620083 Russia *e-mail: [email protected] Received January 19, 2017
Abstract—The geodesic equations for black hole solutions in the scalar–tensor Horndeski gravity model with non-minimal kinetic coupling have been investigated. The ranges of model parameters admitting the existence of bounded orbits have been determined. Constraints on the model parameters providing agreement of the model with the observational data on the accretion and motion of bodies in the Solar system have been obtained. DOI: 10.1134/S1063776117080118
1. INTRODUCTION Present-day observational data suggest that the Universe currently experiences a phase of accelerated expansion [1]. This expansion is described by the introduction of a new component into the formalism of General Relativity (GR), dark energy with a large negative pressure [2]. At present, the trivial dark energy model, the cosmological constant Λ, fits best the observational data. However, the parameters of the equation of state for dark energy obtained in [1], w DE 0 = –1.17(+0.13–0.12), points to dynamical dark energy, because w DE Λ = –1. Thus, the question about the nature of the accelerated expansion of the Universe remains open, and extended gravity models are invoked to explain this phenomenon. The scalar–tensor gravity models are among the best-studied extensions of GR. The most general scalar–tensor gravity model leading to the second-order field equations was proposed by Gregory Horndeski in [3]. The action in the Horndeski model with nonminimal kinetic coupling is
∫
S = dx 4 − g ×(ζ R − η(∂φ) + β G μν∂ μφ∂ νφ − 2Λ), 2
(1)
where Gμν is the Einstein tensor, φ is the scalar field, and the constants ζ > 0, η, and β are model parameters. Although the model can generally also contain other terms with non-minimal kinetic coupling, in this paper we will restrict our analysis to this action, because most of the known spherically symmetric black hole solutions refer precisely to this model.1 The 1 Other
terms of the Horndeski model with non-minimal kinetic coupling also experience problems with the description of neutron stars [4].
model (1) has a set of solutions describing not only compact objects but also the current cosmological expansion and the inflationary stage [5]. Moreover, for η ≠ 0 the model contains solutions in which the vacuum cosmological constant is completely screened, while the background metric describes a de Sitter Universe with an effective cosmological constant proportional to η/β. Thus, the problem of a small vacuum cosmological constant is solved in this model in an interesting way. Any modification of GR must satisfactorily describe phenomena in the Solar system and astrophysical phenomena, which imposes stringent constraints on the possible deviations from GR. The goal of this paper is to continue the study of th
Data Loading...
