Gravitational lensing by f(R,T) gravity

2016 ◽  
Vol 25 (02) ◽  
pp. 1650020 ◽  
Author(s):  
Ahmed Alhamzawi ◽  
Rahim Alhamzawi
Keyword(s):  
General Relativity ◽  
Gravitational Lensing ◽  
Modified Gravity ◽  
Slight Modification ◽  
Schwarzschild Metric ◽  
Considerable Contribution ◽  
Type Formula ◽  
Specific Formula

A solution for [Formula: see text] gravity of the type [Formula: see text] for specific [Formula: see text] functions is derived. It is shown that a slight modification to the Schwarzschild metric can be found for [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] is some constant. The effects of [Formula: see text] gravity on gravitational lensing are calculated and the differences with general relativity are compared. Furthermore, it is shown that modified gravity can give a considerable contribution to gravitational lensing.

scholarly journals One gravitational potential or two? Forecasts and tests

2011 ◽  
Vol 369 (1957) ◽  
pp. 4947-4961 ◽  
Author(s):  
Edmund Bertschinger
Keyword(s):  
General Relativity ◽  
Gravitational Potential ◽  
Gravitational Lensing ◽  
Modified Gravity ◽  
Newtonian Potential ◽  
Newtonian Gravity ◽  
Peculiar Velocities ◽  
Modified Gravity Theories ◽  
Curvature Potential ◽  
The Difference

The metric of a perturbed Robertson–Walker space–time is characterized by three functions: a scale-factor giving the expansion history and two potentials that generalize the single potential of Newtonian gravity. The Newtonian potential induces peculiar velocities and, from these, the growth of matter fluctuations. Massless particles respond equally to the Newtonian potential and to a curvature potential. The difference of the two potentials, called the gravitational slip, is predicted to be very small in general relativity, but can be substantial in modified gravity theories. The two potentials can be measured, and gravity tested on cosmological scales, by combining weak gravitational lensing or the integrated Sachs–Wolfe effect with galaxy peculiar velocities or clustering.

scholarly journals Traversable wormholes with exponential shape function in modified gravity and general relativity: A comparative study

2020 ◽  
Vol 29 (09) ◽  
pp. 2050068 ◽  
Author(s):  
Gauranga C. Samanta ◽  
Nisha Godani ◽  
Kazuharu Bamba
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Comparative Study ◽  
Modified Gravity ◽  
Shape Function ◽  
Anisotropy Parameter ◽  
Energy Conditions ◽  
Traversable Wormholes

We have proposed a novel shape function on which the metric that models traversable wormholes is dependent. Using this shape function, the energy conditions, equation-of-state and anisotropy parameter are analyzed in [Formula: see text] gravity, [Formula: see text] gravity and general relativity. Furthermore, the consequences obtained with respect to these theories are compared. In addition, the existence of wormhole geometries is investigated.

BOUNDS ON f(G) GRAVITY FROM ENERGY CONDITIONS

2010 ◽  
Vol 25 (27) ◽  
pp. 2325-2332 ◽  
Author(s):  
PUXUN WU ◽  
HONGWEI YU
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Modified Gravity ◽  
Energy Conditions ◽  
Model Parameters ◽  
Effective Energy ◽  
Raychaudhuri Equation ◽  
Accelerating Expansion

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρm + ρE and p → pm + pE, where ρE and pE are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

All classical predictions of general relativity from special relativistic Hamiltonian dynamics

2018 ◽  
Vol 33 (29) ◽  
pp. 1850169
Author(s):  
J. H. Field
Keyword(s):  
General Relativity ◽  
Euclidean Space ◽  
Hamiltonian Dynamics ◽  
Gravitational Redshift ◽  
Newtonian Mechanics ◽  
Light Deflection ◽  
Schwarzschild Metric ◽  
Related Literature ◽  
General Relativistic ◽  
Relativistic Hamiltonian Dynamics

Previous special relativistic calculations of gravitational redshift, light deflection and Shapiro delay are extended to include perigee advance. The three classical, order G, post-Newtonian predictions of general relativity as well as general relativistic light-speed-variation are therefore shown to be also consequences of special relativistic Newtonian mechanics in Euclidean space. The calculations are compared to general relativistic ones based on the Schwarzschild metric equation, and related literature is critically reviewed.

scholarly journals The radiation instability in modified gravity

2021 ◽  
Vol 36 (08n09) ◽  
pp. 2150060
Author(s):  
Spiros Cotsakis ◽  
Dimitrios Trachilis
Keyword(s):  
General Relativity ◽  
General Solution ◽  
Modified Gravity ◽  
Evolution Equations ◽  
Formal Series ◽  
Series Expansions ◽  
General Polynomial ◽  
Theories Of Gravity ◽  
Polynomial Extensions

We study the problem of the instability of inhomogeneous radiation universes in quadratic Lagrangian theories of gravity written as a system of evolution equations with constraints. We construct formal series expansions and show that the resulting solutions have a smaller number of arbitrary functions than that required in a general solution. These results continue to hold for more general polynomial extensions of general relativity.

scholarly journals Dark matter in logarithmic F(R) gravity

2019 ◽  
Vol 28 (12) ◽  
pp. 1950157 ◽  
Author(s):  
Tomohiro Inagaki ◽  
Yamato Matsuo ◽  
Hiroki Sakamoto
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Modified Gravity ◽  
Field Method ◽  
Quantum Corrections ◽  
Prototype Model ◽  
Wide Range ◽  
Modified Gravity Theories ◽  
Primordial Inflation ◽  
Cmb Fluctuations

The logarithmic [Formula: see text]-corrected [Formula: see text] gravity is investigated as a prototype model of modified gravity theories with quantum corrections. By using the auxiliary field method, the model is described by the general relativity with a scalaron field. The scalaron field can be identified as an inflaton at the primordial inflation era. It is also one of the dark matter candidates in the dark energy (DE) era. It is found that a wide range of the parameters is consistent with the current observations of CMB fluctuations, DE and dark matter.

scholarly journals Strategies of motion under the black hole horizon

2020 ◽  
Vol 29 (03) ◽  
pp. 2030003
Author(s):  
A. V. Toporensky ◽  
O. B. Zaslavskii
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
First Principles ◽  
Proper Time ◽  
Black Hole Horizon ◽  
Schwarzschild Metric ◽  
Peculiar Velocity ◽  
Peculiar Velocities ◽  
Visible Part ◽  
Methodological Paper

In this methodological paper, we consider two problems an astronaut faces under the black hole horizon in the Schwarzschild metric. (1) How to maximize the survival proper time. (2) How to make a visible part of the outer universe as large as possible before hitting the singularity. Our consideration essentially uses the concept of peculiar velocities based on the “river model.” Let an astronaut cross the horizon from the outside. We reproduce from the first principles the known result that point (1) requires that an astronaut turn off the engine near the horizon and follow the path with the momentum equal to zero. We also show that point (2) requires maximizing the peculiar velocity of the observer. Both goals (1) and (2) require, in general, different strategies inconsistent with each other that coincide at the horizon only. The concept of peculiar velocities introduced in a direct analogy with cosmology and its application for the problems studied in this paper can be used in advanced general relativity courses.

Solar Eclipses as a Teaching Opportunity in Relativity

2020 ◽  
Vol 02 (02) ◽  
pp. 2050010
Author(s):  
James Overduin ◽  
Kelsey Glazer ◽  
Keri McClelland ◽  
Amelia Genus ◽  
Chris Miskiewicz
Keyword(s):  
General Relativity ◽  
Gravitational Lensing ◽  
Pivotal Role ◽  
Light Deflection ◽  
British Government ◽  
Composite Image ◽  
Theory Of Gravity ◽  
Solar Eclipses

Total solar eclipses represent a challenging but spectacular opportunity to introduce curious students to the wonders of general relativity through the phenomenon of light deflection (gravitational lensing). During the Great American Eclipse of 2017, we were among a small number of teams attempting to repeat Eddington’s iconic observations of 1919, which played a pivotal role in establishing Einstein’s theory as the governing theory of gravity. We were not quite successful on the observational front, but acquired an excellent composite image from a fellow astronomer. Analysis of this image allowed us to obtain a result consistent with Einstein’s theory. It is remarkable that such an experiment, which once required the resources of the British government, can now be attempted with reasonable hope of success by teachers and their students. We look forward to our next chance in 2024.

scholarly journals Gravitational lensing in conformal and emergent gravity

2019 ◽  
Vol 206 ◽  
pp. 07002
Author(s):  
Yen-Kheng Lim ◽  
Qing-hai Wang
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Gravitational Lensing ◽  
Conformal Gravity ◽  
Null Geodesics ◽  
Linear Coefficient ◽  
Emergent Gravity ◽  
Bending Of Light

The gravitational bending of light in the framework of conformal gravity is considered where an exact solution for null geodesics in the Mannheim-Kazanas is obtained. The linear coefficient γ characteristic to conformal gravity is shown to contribute enhanced deflection compared to the angle predicted by General Relativity for small γ. We also briefly consider gravitational lensing in covariant emergent gravity.

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