scholarly journals Cosmological constraints on post-Newtonian parameters in effectively massless scalar-tensor theories of gravity

2019 ◽  
Vol 100 (10) ◽  
Author(s):  
Massimo Rossi ◽  
Mario Ballardini ◽  
Matteo Braglia ◽  
Fabio Finelli ◽  
Daniela Paoletti ◽  
...  
Keyword(s):  
Massless Scalar ◽  
Cosmological Constraints ◽  
Theories Of Gravity

scholarly journals ON BOUNDARY TERMS AND CONFORMAL TRANSFORMATIONS IN CURVED SPACETIMES

2002 ◽  
Vol 11 (05) ◽  
pp. 703-714 ◽  
Author(s):  
R. CASADIO ◽  
A. GRUPPUSO
Keyword(s):  
Hamiltonian Formalism ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Conformal Transformations ◽  
Five Dimensions ◽  
Four Dimensions ◽  
Boundary Terms ◽  
Pure Gravity ◽  
Theories Of Gravity ◽  
Flat Spacetimes

We intend to clarify the interplay between boundary terms and conformal transformations in scalar-tensor theories of gravity. We first consider the action for pure gravity in five dimensions and show that, on compactifing a la Kaluza–Klein to four dimensions, one obtains the correct boundary terms in the Jordan (or String) Frame form of the Brans–Dicke action. Further, we analyze how the boundary terms change under the conformal transformations which lead to the Pauli (or Einstein) frame and to the nonminimally coupled massless scalar field. In particular, we study the behaviour of the total energy in asymptotically flat spacetimes as it results from surface terms in the Hamiltonian formalism.

ON STABILITY OF SIMPLEST NONSINGULAR INFLATIONARY COSMOLOGICAL MODELS WITHIN GENERAL RELATIVITY AND GAUGE THEORIES OF GRAVITY

2004 ◽  
Vol 13 (04) ◽  
pp. 695-707 ◽  
Author(s):  
G. V. VERESHCHAGIN
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Gauge Theories ◽  
Initial Conditions ◽  
Solvable Model ◽  
Cosmological Models ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Theories Of Gravity ◽  
Analysis Of Stability

In this paper we provide approximate analytical analysis of stability of nonsingular inflationary chaotic-type cosmological models. Initial conditions for nonsingular solutions at the bounce correspond to dominance of potential part of the energy density of the scalar field over its kinetic part both within general relativity and gauge theories of gravity. Moreover, scalar field at the bounce exceeds the Planckian value and on expansion stage these models correspond to chaotic inflation. Such solutions can be well approximated by explicitly solvable model with constant effective potential (cosmological term) and massless scalar field during the bounce and on stages of quasi-exponential contraction and expansion. Perturbative analysis shows that nonsingular inflationary solutions are exponentially unstable during contraction stage. This result is compared with numerical calculations.

scholarly journals BORN–INFELD BLACK HOLES COUPLED TO A MASSIVE SCALAR FIELD

2011 ◽  
Vol 20 (13) ◽  
pp. 2471-2496 ◽  
Author(s):  
DANIELA A. GEORGIEVA ◽  
IVAN ZH. STEFANOV ◽  
STOYTCHO S. YAZADJIEV ◽  
MICHAIL D. TODOROV
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Causal Structure ◽  
Analytical Techniques ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Massive Scalar ◽  
Massive Scalar Field ◽  
Theories Of Gravity ◽  
Extremal Black Holes

Born–Infeld black holes in the scalar–tensor theories of gravity with massless scalar field have been recently obtained [I. Stefanov, S. Yazadjiev and M. Todorov, Phys. Rev. D75 (2007) 084036; Mod. Phys. Lett. A.23(34) (2008) 2915; Class. Quantum Gravity26 (2009) 015006]. The aim of the current paper is to study the effect of the inclusion of a potential for the scalar field in the theory, through a combination of analytical techniques and numerical methods. The black holes coupled to a massive scalar field have richer causal structure in comparison to the massless scalar field case. In the former case, the black holes may have a second, inner horizon. The presence of potential for the scalar field allows the existence of extremal black holes for certain values of the mass of the scalar field and the magnetic (electric) charge of the black hole. The solutions are stable against spherically symmetric perturbations. Arguments in favor of the general stability of the solutions coming from the application of the "turning point" method are also presented.

FLAT COSMOLOGICAL MODELS WITH MASSIVE SCALAR FIELD IN GAUGE THEORIES OF GRAVITY

2003 ◽  
Vol 12 (08) ◽  
pp. 1487-1497 ◽  
Author(s):  
G. V. VERESHCHAGIN
Keyword(s):  
Scalar Field ◽  
Gauge Theories ◽  
Cosmological Models ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Massive Scalar ◽  
Effective Equation ◽  
Massive Scalar Field ◽  
Theories Of Gravity ◽  
Contraction Stage

Solutions of gravitational equations of gauge theories of gravity in homogeneous isotropic world with massive scalar field are investigated in the case of flat cosmological models. Special attention is dedicated to behavior of solutions on contraction stage. It is shown, that on expansion stage inflationary solutions are generic feature of the model. At the same time on contraction stage an effective equation of state can be similar to the case of massless scalar field p=ρ at the beginning of evolution and tends to the equation of ultrarelativistic gas p=ρ/3. The Hubble parameter tends to some negative value on contraction stage, depending on the mass of the scalar field. Nonsingular solutions in this model are unstable.

scholarly journals On black hole structures in scalar–tensor theories of gravity

2016 ◽  
Vol 25 (09) ◽  
pp. 1641005 ◽  
Author(s):  
Kirill A. Bronnikov ◽  
Júlio C. Fabris ◽  
Denis C. Rodrigues
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Scalar Field ◽  
Metric Regularity ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Singular Behavior ◽  
Nonminimal Coupling ◽  
Theories Of Gravity ◽  
Scalar Gravity

We review some properties of black hole structures appearing in gravity with a massless scalar field, with both minimal and nonminimal coupling. The main properties of the resulting cold black holes are described. The study of black holes in scalar-gravity systems is extended to [Formula: see text]-essence theories, and some examples are explicitly worked out. In these cases, even while the existence of horizons is possible, the metric regularity requirement on the horizon implies either a cold black type structure or a singular behavior of the scalar field.

scholarly journals Constraining Modified Theories of Gravity with Gravitational-Wave Stochastic Backgrounds

2016 ◽  
Vol 117 (9) ◽  
Author(s):  
Andrea Maselli ◽  
Stefania Marassi ◽  
Valeria Ferrari ◽  
Kostas Kokkotas ◽  
Raffaella Schneider
Keyword(s):  
Gravitational Wave ◽  
Modified Theories Of Gravity ◽  
Theories Of Gravity ◽  
Stochastic Backgrounds

scholarly journals Quantum extremal islands made easy. Part III. Complexity on the brane

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Juan Hernandez ◽  
Robert C. Myers ◽  
Shan-Ming Ruan
Keyword(s):  
Holographic Model ◽  
Bonnet Gravity ◽  
Higher Curvature Gravity ◽  
Theories Of Gravity

Abstract We examine holographic complexity in the doubly holographic model introduced in [1, 2] to study quantum extremal islands. We focus on the holographic complexity=volume (CV) proposal for boundary subregions in the island phase. Exploiting the Fefferman-Graham expansion of the metric and other geometric quantities near the brane, we derive the leading contributions to the complexity and interpret these in terms of the generalized volume of the island derived from the induced higher-curvature gravity action on the brane. Motivated by these results, we propose a generalization of the CV proposal for higher curvature theories of gravity. Further, we provide two consistency checks of our proposal by studying Gauss-Bonnet gravity and f(ℛ) gravity in the bulk.

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