scholarly journals A study of perturbations in scalar–tensor theory using 1 + 3 covariant approach

2018 ◽  
Vol 27 (03) ◽  
pp. 1850033 ◽  
Author(s):  
Joseph Ntahompagaze ◽  
Amare Abebe ◽  
Manasse Mbonye
Keyword(s):  
Energy Density ◽  
Radiation Energy ◽  
Linear Perturbation ◽  
Scalar Tensor Theory ◽  
Radiation Energy Density ◽  
Tensor Theory ◽  
Density Perturbations ◽  
Theories Of Gravity ◽  
Theory Of Gravitation ◽  
Second Order Equations

This work discusses scalar–tensor theories of gravity, with a focus on the Brans–Dicke sub-class, and one that also takes note of the latter’s equivalence with [Formula: see text] gravitation theories. A [Formula: see text] covariant formalism is used in this case to discuss covariant perturbations on a background Friedmann–Laimaître–Robertson–Walker (FLRW) spacetime. Linear perturbation equations are developed based on gauge-invariant gradient variables. Both scalar and harmonic decompositions are applied to obtain second-order equations. These equations can then be used for further analysis of the behavior of the perturbation quantities in such a scalar–tensor theory of gravitation. Energy density perturbations are studied for two systems, namely for a scalar fluid-radiation system and for a scalar fluid-dust system, for [Formula: see text] models. For the matter-dominated era, it is shown that the dust energy density perturbations grow exponentially, a result which agrees with those already existing in the literatures. In the radiation-dominated era, it is found that the behavior of the radiation energy–density perturbations is oscillatory, with growing amplitudes for [Formula: see text], and with decaying amplitudes for [Formula: see text]. This is a new result.

scholarly journals Bianchi Types II, VIII, and IX String Cosmological Models in Brans-Dicke Theory of Gravitation

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
V. U. M. Rao ◽  
M. Vijaya Santhi
Keyword(s):  
Energy Density ◽  
Cosmological Model ◽  
Bianchi Type ◽  
Cosmological Models ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Geometrical Features ◽  
Viii And Ix ◽  
Theory Of Gravitation ◽  
Bianchi Types

Bianchi types II, VIII, and IX string cosmological models are obtained and presented in a scalar-tensor theory of gravitation proposed by Brans and Dicke (1961) for λ+ρ=0. We also established the existence of only Bianchi type IX vacuum cosmological model for λ=ρ, where λ and ρ are tension density and energy density of strings, respectively. Some physical and geometrical features of the models are also discussed.

Scalar fields in generalized theories of gravity: Limit to general relativity

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040006
Author(s):  
Piret Kuusk
Keyword(s):  
General Relativity ◽  
Scalar Fields ◽  
Einstein Gravity ◽  
Scalar Tensor Theory ◽  
Action Functional ◽  
Tensor Theory ◽  
General Action ◽  
Theories Of Gravity ◽  
Theory Of Gravitation ◽  
Special Case

The general action functional for a scalar-tensor theory of gravitation without derivative couplings is considered together with its special case of the Brans–Dicke theory. The aim of the paper is to clarify the problem of anomalous limit of the Brans–Dicke to the Einstein gravity.

Measurement facility for the relative radiation energy density distribution for pulse-periodic lasers

1988 ◽  
Vol 31 (10) ◽  
pp. 966-967
Author(s):  
V. I. Andreev ◽  
A. P. Palivoda ◽  
S. P. Fetisov ◽  
N. V. Shalomeeva ◽  
V. A. Yakovlev
Keyword(s):  
Energy Density ◽  
Density Distribution ◽  
Radiation Energy ◽  
Measurement Facility ◽  
Radiation Energy Density ◽  
Energy Density Distribution

Features of Brass Processing with Powerful Ultraviolet Lasers of Nanosecond Duration

2022 ◽  
Vol 1049 ◽  
pp. 11-17
Author(s):  
Ivan Kaplunov ◽  
Taras Malinskiy ◽  
S.I. Mikolutskiy ◽  
Vladimir Rogalin ◽  
Yuriy Khomich ◽  
...  
Keyword(s):  
Energy Density ◽  
Metal Structure ◽  
Radiation Energy ◽  
Laser Heat Treatment ◽  
Absorbed Energy ◽  
Radiation Energy Density ◽  
Nanosecond Duration ◽  
Third Harmonic ◽  
Accumulation Of Damage ◽  
Ultraviolet Lasers

We investigated the process of laser heat treatment of polished brass samples (36% zinc, containing a small amount of lead, which does not dissolve in the alloy and is in the form of inclusions, having micron and submicron size) by impacting to a series of 25 - 30 ultraviolet (UV) pulses of a Nd:YAG laser (third harmonic, wavelength λ = 355 nm, duration τ = 10 ns, pulse repetition rate f = 10 Hz, pulse energy density ~ 0.15 - 1.0 J/cm2) in the stationary spot mode. Copper and its alloys absorb up to 90% of the energy of this laser. It is found that the relaxation of the absorbed energy of laser radiation in the metal occurs nonuniformly. Defects in the metal structure such as grain boundaries and lead inclusions are visualized. Traces of crystallographic sliding appear inside some grains. With an increase in the number of impacting impulses, accumulation of damage is observed. A further increase in the radiation energy density leads to an aggravation of the observed phenomena.

scholarly journals Plane Symmetric Solutions of a Scalar-Tensor Theory of Gravitation

1977 ◽  
Vol 30 (1) ◽  
pp. 109 ◽  
Author(s):  
DRK Reddy
Keyword(s):  
General Relativity ◽  
Empty Space ◽  
Scalar Fields ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Plane Symmetric ◽  
Zero Mass ◽  
Tensor Theory ◽  
Special Cases ◽  
Theory Of Gravitation

Plane symmetric solutions of a scalar-tensor theory proposed by Dunn have been obtained. These solutions are observed to be similar to the plane symmetric solutions of the field equations corresponding to zero mass scalar fields obtained by Patel. It is found that the empty space-times of general relativity discussed by Taub and by Bera are obtained as special cases.

scholarly journals Non-Riemannian description of Robinson–Trautman spacetimes in Brans–Dicke theory of gravity

2019 ◽  
Vol 28 (04) ◽  
pp. 1950070
Author(s):  
Muzaffer Adak ◽  
Tekin Dereli ◽  
Yorgo Şenikoğlu
Keyword(s):  
Scalar Field ◽  
Differential Forms ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Exterior Differential ◽  
Tensor Theory ◽  
Theory Of Gravitation ◽  
Theory Of Gravity ◽  
Future Reference

The variational field equations of Brans–Dicke scalar-tensor theory of gravitation are given in a non-Riemannian setting in the language of exterior differential forms over four-dimensional spacetimes. A conformally rescaled Robinson–Trautman metric together with the Brans–Dicke scalar field are used to characterize algebraically special Robinson–Trautman spacetimes. All the relevant tensors are worked out in a complex null basis and given explicitly in an appendix for future reference. Some special families of solutions are also given and discussed.

Sign in / Sign up

Export Citation Format

Share Document