Cosmological graviton production in general relativity and related gravity theories

1994 ◽  
Vol 50 (10) ◽  
pp. 6262-6296 ◽  
Author(s):  
Márcio R. de Garcia Maia ◽  
John D. Barrow
Keyword(s):  
General Relativity ◽  
Gravity Theories

scholarly journals PRINCIPLES OF EINSTEIN–FINSLER GRAVITY AND PERSPECTIVES IN MODERN COSMOLOGY

2012 ◽  
Vol 21 (09) ◽  
pp. 1250072 ◽  
Author(s):  
SERGIU I. VACARU
Keyword(s):  
General Relativity ◽  
Lorentz Invariance ◽  
Frame Structure ◽  
Relativity Theory ◽  
Finsler Metrics ◽  
Finsler Spaces ◽  
Modern Cosmology ◽  
Gravity Theories ◽  
Tangent Bundles ◽  
Local Lorentz Invariance

We study the geometric and physical foundations of Finsler gravity theories with metric compatible connections defined on tangent bundles, or (pseudo) Riemannian manifolds, endowed with nonholonomic frame structure. Several generalizations and alternatives to Einstein gravity are considered, including modifications with broken local Lorentz invariance. It is also shown how such theories (and general relativity) can be equivalently re-formulated in Finsler like variables. We focus on prospects in modern cosmology and Finsler acceleration of Universe. Einstein–Finsler gravity theories are elaborated following almost the same principles as in the general relativity theory but extended to Finsler metrics and connections. Finally, some examples of generic off-diagonal metrics and generalized connections, defining anisotropic cosmological Einstein–Finsler spaces are analyzed; certain criteria for the Finsler accelerating evolution are formulated.

scholarly journals What if Newton’s Gravitational Constant Was Negative?

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 38
Author(s):  
Ismael Ayuso ◽  
José Mimoso ◽  
Nelson Nunes
Keyword(s):  
Field Theory ◽  
General Relativity ◽  
Gravitational Constant ◽  
Gravitational Coupling ◽  
Coupling Constant ◽  
De Sitter ◽  
Quadratic Potential ◽  
Gravitational Coupling Constant ◽  
General Scalar ◽  
Gravity Theories

In this work, we seek a cosmological mechanism that may define the sign of the effective gravitational coupling constant, G. To this end, we consider general scalar-tensor gravity theories as they provide the field theory natural framework for the variation of the gravitational coupling. We find that models with a quadratic potential naturally stabilize the value of G into the positive branch of the evolution and further, that de Sitter inflation and a relaxation to General Relativity is easily attained.

scholarly journals Relation between general relativity and a class of Hořava gravity theories

2021 ◽  
Vol 103 (8) ◽  
Author(s):  
Nicola Franchini ◽  
Mario Herrero-Valea ◽  
Enrico Barausse
Keyword(s):  
General Relativity ◽  
Horava Gravity ◽  
Gravity Theories

scholarly journals Blackhole in nonlocal gravity: comparing metric from Newmann–Janis algorithm with slowly rotating solution

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Utkarsh Kumar ◽  
Sukanta Panda ◽  
Avani Patel
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Modified Gravity ◽  
Kerr Metric ◽  
Slow Rotation ◽  
Field Equations ◽  
External Region ◽  
Modified Gravity Theories ◽  
Spacetime Metric ◽  
Gravity Theories

Abstract The strong gravitational field near massive blackhole is an interesting regime to test General Relativity (GR) and modified gravity theories. The knowledge of spacetime metric around a blackhole is a primary step for such tests. Solving field equations for rotating blackhole is extremely challenging task for the most modified gravity theories. Though the derivation of Kerr metric of GR is also demanding job, the magical Newmann–Janis algorithm does it without actually solving Einstein equation for rotating blackhole. Due to this notable success of Newmann–Janis algorithm in the case of Kerr metric, it has been being used to obtain rotating blackhole solution in modified gravity theories. In this work, we derive the spacetime metric for the external region of a rotating blackhole in a nonlocal gravity theory using Newmann–Janis algorithm. We also derive metric for a slowly rotating blackhole by perturbatively solving field equations of the theory. We discuss the applicability of Newmann–Janis algorithm to nonlocal gravity by comparing slow rotation limit of the metric obtained through Newmann–Janis algorithm with slowly rotating solution of the field equation.

NON-RIEMANNIAN THEORIES OF GRAVITY AND LUNAR AND SATELLITE LASER RANGING

1992 ◽  
Vol 07 (04) ◽  
pp. 843-852 ◽  
Author(s):  
IGNAZIO CIUFOLINI ◽  
RICHARD MATZNER
Keyword(s):  
General Relativity ◽  
Riemannian Manifold ◽  
Satellite Laser Ranging ◽  
Laser Ranging ◽  
Riemannian Spacetime ◽  
Theories Of Gravity ◽  
Alternative Gravity Theories ◽  
Gravity Theories ◽  
Einstein’S General Relativity ◽  
Alternative Gravity

Theories of gravity with a non-Riemannian manifold have been studied since the advent of Einstein's general relativity. In this paper, after an introduction on theories of gravity with a non-Riemannian spacetime and in particular on the nonsymmetric Moffat theory, we briefly describe the techniques of lunar and satellite laser ranging. Among the various applications of lunar and satellite laser ranging are several important measurements and tests of Einstein's general relativity as well as constraints on some alternative gravity theories. In particular, lunar and satellite laser ranging put strong validity limits on the 1983 nonsymmetric Moffat theory.

scholarly journals Gravitational light deflection, time delay and frequency shift in Einstein-Aether theory

2009 ◽  
Vol 5 (S261) ◽  
pp. 140-143
Author(s):  
Kai Tang ◽  
Tian-Yi Huang ◽  
Zheng-Hong Tang
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Time Delay ◽  
Frequency Shift ◽  
Light Propagation ◽  
Gravity Theory ◽  
Light Deflection ◽  
Body Model ◽  
Newtonian Approximation ◽  
Gravity Theories

AbstractEinstein-Aether gravity theory has been proven successful in passing experiments of different scales. Especially its Eddington parameters β and γ have the same numerical values as those in general relativity. Recently Xie and Huang (2008) have advanced this theory to a second post-Newtonian approximation for an N-body model and obtained an explicit metric when the bodies are point-like masses. This research considers light propagation in the above gravitational field, and explores the light deflection, time delay, frequency shift etc. The results will provide for future experiments in testing gravity theories.

scholarly journals Quasilocal quantities for general relativity and other gravity theories

1999 ◽  
Vol 16 (4) ◽  
pp. 1279-1304 ◽  
Author(s):  
Chiang-Mei Chen ◽  
James M Nester
Keyword(s):  
General Relativity ◽  
Gravity Theories

scholarly journals Strong gravity signatures in the polarization of gravitational waves

2019 ◽  
Vol 28 (14) ◽  
pp. 1944020 ◽  
Author(s):  
S. Shankaranarayanan
Keyword(s):  
General Relativity ◽  
Gravitational Wave ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Strong Field ◽  
Normal Modes ◽  
Strong Gravity ◽  
Modified Gravity Theories ◽  
Gravitational Wave Detectors ◽  
Gravity Theories

General Relativity is a hugely successful description of gravitation. However, both theory and observations suggest that General Relativity might have significant classical and quantum corrections in the Strong Gravity regime. Testing the strong field limit of gravity is one of the main objectives of the future gravitational wave detectors. One way to detect strong gravity is through the polarization of gravitational waves. For quasi-normal modes of black-holes in General Relativity, the two polarization states of gravitational waves have the same amplitude and frequency spectrum. Using the principle of energy conservation, we show that the polarizations differ for modified gravity theories. We obtain a diagnostic parameter for polarization mismatch that provides a unique way to distinguish General Relativity and modified gravity theories in gravitational wave detectors.

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