scholarly journals Bispectrum of cosmological density perturbations in the most general second-order scalar-tensor theory

2014 ◽  
Vol 89 (10) ◽  
Author(s):  
Yuichiro Takushima ◽  
Ayumu Terukina ◽  
Kazuhiro Yamamoto
Keyword(s):  
Second Order ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Density Perturbations

scholarly journals 1 + 3 covariant perturbations in power-law f(R) gravity

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Beatrice Murorunkwere ◽  
Joseph Ntahompagaze ◽  
Edward Jurua
Keyword(s):  
Differential Equations ◽  
Evolution Equations ◽  
Numerical Solutions ◽  
Background Solution ◽  
Scalar Tensor Theory ◽  
Covariant Approach ◽  
Tensor Theory ◽  
Harmonic Decomposition ◽  
Density Perturbations ◽  
Perturbation Equations

AbstractWe applied the 1+3 covariant approach around the Friedmann–Lemaître–Robertson–Walker (FLRW) background, together with the equivalence between f(R) gravity and scalar-tensor theory to study cosmological perturbations. We defined the gradient variables in the 1 + 3 covariant approach which we used to derive a set of evolution equations. Harmonic decomposition was applied to partial differential equations to obtain ordinary differential equations used to analyse the behavior of the perturbation quantities. We focused on dust dominated area and the perturbation equations were applied to background solution of $$\alpha R+\beta R^{n}$$ α R + β R n model, n being a positive constant. The transformation of the perturbation equations into redshift dependence was done. After numerical solutions, it was found that the evolution of energy-density perturbations in a dust-dominated universe for different values of n decays with increasing redshift.

scholarly journals Formation and Clustering of Primordial Black Holes in Brans-Dicke Theory

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 158
Author(s):  
Victor Berezin ◽  
Vyacheslav Dokuchaev ◽  
Yury Eroshenko ◽  
Alexey Smirnov
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Gravitational Wave ◽  
Significant Contribution ◽  
Threshold Value ◽  
Primordial Black Holes ◽  
Cosmological Horizon ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Density Perturbations

The formation of primordial black holes in the early universe in the Brans-Dicke scalar-tensor theory of gravity is investigated. Corrections to the threshold value of density perturbations are found. Above the threshold, the gravitational collapse occurs after the cosmological horizon crossing. The corrections depend in a certain way on the evolving scalar field. They affect the probability of primordial black holes formation, and can lead to their clustering at large scales if the scalar field is inhomogeneous. The formation of the clusters, in turn, increases the probability of black holes merge and the corresponding rate of gravitational wave bursts. The clusters can provide a significant contribution to the LIGO/Virgo gravitational wave events, if part of the observed events are associated with primordial black holes.

scholarly journals General Second-Order Scalar-Tensor Theory and Self-Tuning

2012 ◽  
Vol 108 (5) ◽  
Author(s):  
Christos Charmousis ◽  
Edmund J. Copeland ◽  
Antonio Padilla ◽  
Paul M. Saffin
Keyword(s):  
Second Order ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Self Tuning

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 The most general second-order field equations of bi-scalar-tensor theory in four dimensions

2015 ◽  
Vol 2015 (7) ◽  
Author(s):  
Seiju Ohashi ◽  
Norihiro Tanahashi ◽  
Tsutomu Kobayashi ◽  
Masahide Yamaguchi
Keyword(s):  
Second Order ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Four Dimensions ◽  
Tensor Theory
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