scholarly journals Tests of modified gravity theories in the Solar System

2015 ◽  
Vol 93 (2) ◽  
pp. 151-165
Author(s):  
Ali Mozaffari
Keyword(s):  
Gravitational Field ◽  
Solar System ◽  
Modified Gravity ◽  
Saddle Points ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Modified Gravity Theories ◽  
Different Types ◽  
Theories Of Gravity ◽  
Positive Results

We review the case for testing preferred acceleration scale theories of gravity (sometimes falling under the guise of modified Newtonian dynamics) in the Solar System using the forthcoming LISA Pathfinder (LPF) mission. Using a combination of analytical and numerical results, we suggest that different types of theory should be detectable using the predicted anomalous tidal stresses effects around the saddle points of the Newtonian gravitational field. The saddle point bubbles’ expected extent of ∼400 km are to be contrasted with potential miss parameters of ≤10 km, making such a test in easy reach of LPF. We also consider routes to constraining our theories from data, based on scenarios of both null and positive results.

TESTING STRONG MOND BEHAVIOR IN THE SOLAR SYSTEM

2007 ◽  
Vol 16 (12a) ◽  
pp. 2035-2053 ◽  
Author(s):  
JOÃO MAGUEIJO ◽  
JACOB BEKENSTEIN
Keyword(s):  
Solar System ◽  
Saddle Point ◽  
Gravitational Potential ◽  
Saddle Points ◽  
Space Missions ◽  
Newtonian Theory ◽  
Modified Newtonian Dynamics ◽  
Lisa Pathfinder ◽  
Oblate Ellipsoid ◽  
Newtonian Dynamics

We summarize an interesting set of solar system predictions that we have recently derived for modified Newtonian dynamics (MOND). Specifically, we find that strong MOND behavior may become evident near the saddle points of the total gravitational potential. Whereas in Newtonian theory tidal stresses are finite at saddle points, they are expected to diverge in MOND, and to remain distinctly large inside a sizable oblate ellipsoid around the saddle point. While strong MOND behavior would be a spectacular "backyard" vindication of the theory, pinpointing the MOND bubbles in the setting of the realistic solar system may be difficult. Space missions such as the LISA Pathfinder, equipped with sensitive accelerometers, may be able to explore the larger perturbative region.

scholarly journals A logarithmic correction in the entropy functional formalism

2016 ◽  
Vol 25 (07) ◽  
pp. 1650080 ◽  
Author(s):  
Fayçal Hammad ◽  
Mir Faizal
Keyword(s):  
Quantum Gravity ◽  
Modified Gravity ◽  
Correction Term ◽  
Modified Theories Of Gravity ◽  
Logarithmic Correction ◽  
Functional Formalism ◽  
Entropy Formula ◽  
Entropy Functional ◽  
Modified Gravity Theories ◽  
Theories Of Gravity

The entropy functional formalism allows one to recover general relativity, modified gravity theories, as well as the Bekenstein–Hawking entropy formula. In most approaches to quantum gravity, the Bekenstein–Hawking’s entropy formula acquires a logarithmic correction term. As such terms occur almost universally in most approaches to quantum gravity, we analyze the effect of such terms on the entropy functional formalism. We demonstrate that the leading correction to the micro-canonical entropy in the entropy functional formalism can be used to recover modified theories of gravity already obtained with an uncorrected micro-canonical entropy. Furthermore, since the entropy functional formalism reproduces modified gravity, the rise of gravity-dependent logarithmic corrections turns out to be one way to impose constraints on these theories of modified gravity. The constraints found here for the simple case of an [Formula: see text]-gravity are the same as those obtained in the literature from cosmological considerations.

scholarly journals Testing quasilinear modified Newtonian dynamics in the Solar System

2012 ◽  
Vol 86 (4) ◽  
Author(s):  
Pasquale Galianni ◽  
Martin Feix ◽  
Hongsheng Zhao ◽  
Keith Horne
Keyword(s):  
Solar System ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics

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 The Train Wreck Cluster Abell 520 and the Bullet Cluster 1E0657-558 in a Generalized Theory of Gravitation

Galaxies ◽  
2018 ◽  
Vol 6 (2) ◽  
pp. 41 ◽  
Author(s):  
Norman Israel ◽  
John Moffat
Keyword(s):  
Dark Matter ◽  
Gravitational Field ◽  
Modified Gravity ◽  
Gravitational Theory ◽  
Field Limit ◽  
X Ray ◽  
Weak Gravitational Field ◽  
Modified Gravity Theories ◽  
Theory Of Gravitation ◽  
Map Data

A major hurdle for modified gravity theories is to explain the dynamics of galaxy clusters. A case is made for a generalized gravitational theory called Scalar-Tensor-Vector-Gravity (STVG) or MOG (Modified Gravity) to explain merging cluster dynamics. The paper presents the results of a re-analysis of the Bullet Cluster, as well as an analysis of the Train Wreck Cluster in the weak gravitational field limit without dark matter. The King- β model is used to fit the X-ray data of both clusters, and the κ -maps are computed using the parameters of this fit. The amount of galaxies in the clusters is estimated by subtracting the predicted κ -map from the κ -map data. The estimate for the Bullet Cluster is that 14.1 % of the cluster is composed of galaxies. For the Train Wreck Cluster, if the Jee et al. data are used, 25.7 % of the cluster is composed of galaxies. The baryon matter in the galaxies and the enhanced strength of gravitation in MOG shift the lensing peaks, making them offset from the gas. The work demonstrates that this generalized gravitational theory can explain merging cluster dynamics without dark matter.

scholarly journals Tensor–vector–scalar-modified gravity: from small scale to cosmology

2011 ◽  
Vol 369 (1957) ◽  
pp. 5003-5017 ◽  
Author(s):  
Jacob D. Bekenstein
Keyword(s):  
Gravitational Lensing ◽  
Modified Gravity ◽  
Gravity Theory ◽  
Small Scale ◽  
Scalar Theory ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Modified Gravity Theory ◽  
The Face ◽  
Standard Cosmological Model

The impressive success of the standard cosmological model has suggested to many that its ingredients are all that one needs to explain galaxies and their systems. I summarize a number of known problems with this programme. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the modified Newtonian dynamics (MOND) paradigm, which has proved to be an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the non-relativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first side-stepped with the formulation of tensor–vector–scalar theory (T e V e  S), a covariant-modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in the face of galaxy phenomenology. I also summarize features of T e V e  S cosmology and describe the confrontation with data from strong and weak gravitational lensing.

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