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 HALO MODELS IN MODIFIED GRAVITY THEORIES WITH SELF-ACCELERATED EXPANSION

2011 ◽  
Vol 20 (12) ◽  
pp. 2383-2397 ◽  
Author(s):  
TATSUYA NARIKAWA ◽  
RAMPEI KIMURA ◽  
TATSUNOSUKE YANO ◽  
KAZUHIRO YAMAMOTO
Keyword(s):  
Gravity Model ◽  
Modified Gravity ◽  
Outer Region ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Newtonian Gravity ◽  
Sphere Model ◽  
Modified Gravity Theories ◽  
The Common ◽  
The Difference

We investigate the structure of halos in the sDGP (self-accelerating branch of the Dvali–Gavadadze–Porrati braneworld gravity) model and the Galileon modified gravity model on the basis of the static and spherically symmetric solutions of the collisionless Boltzmann equation, which reduce to the singular isothermal sphere model and the King model in the limit of Newtonian gravity. The common feature of these halos is that the density of a halo in the outer region is larger (smaller) in the sDGP (Galileon) model, respectively, in comparison with Newtonian gravity. This comes from the suppression (enhancement) of the effective gravity at large distance in the sDGP (Galileon) model, respectively. However, the difference between these modified gravity models and Newtonian gravity only appears outside the halo due to the Vainshtein mechanism, which makes it difficult to distinguish between them. We also discuss the case in which the halo density profile is fixed independently of the gravity model for comparison between our results and previous work.

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 Large-scale structure probes of modified gravity

2018 ◽  
Vol 27 (15) ◽  
pp. 1848005 ◽  
Author(s):  
Catherine Heymans ◽  
Gong-Bo Zhao
Keyword(s):  
Gravitational Lensing ◽  
Modified Gravity ◽  
Large Scale ◽  
Information Gain ◽  
Einstein Gravity ◽  
Large Scale Structures ◽  
Modified Gravity Theories ◽  
Scale Structures ◽  
The Impact ◽  
The Universe

Observations of the evolution of large-scale structures in the Universe provides unique tools to confront Einstein’s theory of General Relativity on cosmological scales. We review weak gravitational lensing and galaxy clustering studies, discussing how these can be used in combination in order to constrain a range of different modified gravity theories. We argue that in order to maximise the future information gain from these probes, theoretical effort will be required in order to model the impact of beyond-Einstein gravity in the nonlinear regime of structure formation.

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.

scholarly journals Cosmic voids in modified gravity scenarios

2019 ◽  
Vol 632 ◽  
pp. A52 ◽  
Author(s):  
Eder L. D. Perico ◽  
Rodrigo Voivodic ◽  
Marcos Lima ◽  
David F. Mota
Keyword(s):  
General Relativity ◽  
Modified Gravity ◽  
Gravitational Theory ◽  
Gravity Models ◽  
Consistency Check ◽  
Dark Sector ◽  
Modified Gravity Theories ◽  
Acceleration Of The Universe ◽  
Best Fit ◽  
The Universe

Modified gravity (MG) theories aim to reproduce the observed acceleration of the Universe by reducing the dark sector while simultaneously recovering General Relativity (GR) within dense environments. Void studies appear to be a suitable scenario to search for imprints of alternative gravity models on cosmological scales. Voids cover an interesting range of density scales where screening mechanisms fade out, which reaches from a density contrast δ ≈ −1 close to their centers to δ ≈ 0 close to their boundaries. We present an analysis of the level of distinction between GR and two modified gravity theories, the Hu–Sawicki f(R) and the symmetron theory. This study relies on the abundance, linear bias, and density profile of voids detected in N-body cosmological simulations. We define voids as connected regions made up of the union of spheres with a mean density given by ρ̅v = 0.2 ρ̅m, but disconnected from any other voids. We find that the height of void walls is considerably affected by the gravitational theory, such that it increases for stronger gravity modifications. Finally, we show that at the level of dark matter N-body simulations, our constraints allow us to distinguish between GR and MG models with |fR0| > 10−6 and zSSB >  1. Differences of best-fit values for MG parameters that are derived independently from multiple void probes may indicate an incorrect MG model. This serves as an important consistency check.

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 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.

scholarly journals Testing dispersion of gravitational waves from eccentric extreme-mass-ratio inspirals

2019 ◽  
Vol 28 (15) ◽  
pp. 1950166
Author(s):  
Shu-Cheng Yang ◽  
Wen-Biao Han ◽  
Shuo Xin ◽  
Chen Zhang
Keyword(s):  
General Relativity ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Arrival Time ◽  
Graviton Mass ◽  
Mass Ratio ◽  
Dispersion Effect ◽  
Intermediate Mass ◽  
Modified Gravity Theories ◽  
Better Than

In general relativity, there is no dispersion in gravitational waves, while some modified gravity theories predict dispersion phenomena in the propagation of gravitational waves. In this paper, we demonstrate that this dispersion will induce an observable deviation of waveforms if the orbits have large eccentricities. The mechanism is that the waveform modes with different frequencies will be emitted at the same time due to the existence of eccentricity. During the propagation, because of the dispersion, the arrival time of different modes will be different, then produce the deviation and dephasing of waveforms compared with general relativity. This kind of dispersion phenomena related with extreme-mass-ratio inspirals could be observed by space-borne detectors, and the constraint on the graviton mass could be improved. Moreover, we find that the dispersion effect may also be constrained by ground detectors better than the current result if a highly eccentric intermediate-mass-ratio inspirals be observed.

scholarly journals Generic off-diagonal solutions and solitonic hierarchies in (modified) gravity

2015 ◽  
Vol 30 (19) ◽  
pp. 1550090 ◽  
Author(s):  
Sergiu I. Vacaru
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Modified Gravity ◽  
Field Equations ◽  
Physical Data ◽  
Modified Gravity Theories ◽  
De Vries ◽  
Einstein Spaces ◽  
Curve Flows ◽  
Gravity Theories

We have summarized our recent results on encoding exact solutions of field equations in Einstein and modified gravity theories into solitonic hierarchies derived for nonholonomic curve flows with associated bi-Hamilton structure. We argue that there is a canonical distinguished connection for which the fundamental geometric/physical equations decouple in general form. This allows us to construct very general classes of generic off-diagonal solutions determined by corresponding types of generating and integration functions depending on all (spacetime) coordinates. If the integral varieties are constrained to zero torsion configurations, we can extract solutions for the general relativity (GR) theory. We conclude that the geometric and physical data for various classes of effective/modified Einstein spaces can be encoded into multi-component versions of the sine-Gordon, or modified Korteweg–de Vries equations.

scholarly journals On the Lambda-evolution of galaxy clusters

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
V. G. Gurzadyan ◽  
A. A. Kocharyan ◽  
A. Stepanian
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Galaxy Clusters ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Cosmological Time ◽  
The Common ◽  
Common Nature ◽  
The Difference ◽  
Evolutionary Paths

AbstractThe evolution of galaxy clusters can be affected by the repulsion described by the cosmological constant. This conclusion is reached within the modified weak-field General Relativity approach where the cosmological constant $$\varLambda $$Λ enables to describe the common nature of the dark matter and the dark energy. Geometrical methods of theory of dynamical systems and the Ricci curvature criterion are used to reveal the difference in the instability properties of galaxy clusters which determine their evolutionary paths. Namely, it is shown that the clusters determined by gravity with $$\varLambda $$Λ-repulsion tend to become even more unstable than those powered only by Newtonian gravity, the effect to be felt at cosmological time scales.

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