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.

scholarly journals ASTROPHYSICAL CONDITION ON THE ATTOLENSING AS A POSSIBLE PROBE FOR A MODIFIED GRAVITY THEORY

2008 ◽  
Vol 23 (01) ◽  
pp. 167-179
Author(s):  
TAKAHIRO SATO ◽  
BOBBY E. GUNARA ◽  
KAZUHIRO YAMAMOTO ◽  
FREDDY P. ZEN
Keyword(s):  
Black Hole ◽  
Relative Motion ◽  
Gravitational Lensing ◽  
Modified Gravity ◽  
Source Size ◽  
Gravity Theory ◽  
Solar Mass ◽  
Wave Effect ◽  
Modified Gravity Theory ◽  
Astrophysical Condition

We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10-19 M sun (solar mass), which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed.

scholarly journals Gravitational lensing by exotic objects

2017 ◽  
Vol 32 (34) ◽  
pp. 1730031 ◽  
Author(s):  
Hideki Asada
Keyword(s):  
Time Delay ◽  
Equation Of State ◽  
Gravitational Lensing ◽  
Modified Gravity ◽  
Standard Form ◽  
Phenomenological Approach ◽  
Gravity Theory ◽  
Gravitational Lens ◽  
Lens Model ◽  
Modified Gravity Theory

This paper reviews a phenomenological approach to the gravitational lensing by exotic objects such as the Ellis wormhole lens, where the exotic lens objects may follow a non-standard form of the equation of state or may obey a modified gravity theory. A gravitational lens model is proposed in the inverse powers of the distance, such that the Schwarzschild lens and exotic lenses can be described in a unified manner as a one parameter family. As observational implications, the magnification, shear, photo-centroid motion and time delay in this lens model are discussed.

scholarly journals A Modified Gravity Theory: Null Aether

2019 ◽  
Vol 71 (3) ◽  
pp. 312 ◽  
Author(s):  
Metin Gürses ◽  
Çetin Şentürk
Keyword(s):  
Modified Gravity ◽  
Gravity Theory ◽  
Modified Gravity Theory

MODIFIED GRAVITY THEORY DUE TO POSITIVE AS WELL AS NEGATIVE CURVATURE INDUCED ACCELERATION

2012 ◽  
Vol 21 (02) ◽  
pp. 1250012
Author(s):  
PRIYADARSHI MAJUMDAR
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Negative Curvature ◽  
Gravity Theory ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Negative Power ◽  
Modified Gravity Theory ◽  
Phase Q ◽  
The Universe

We formulate a modified gravity theory that eliminates the need for dark energy and is stable for a Lagrangian containing R, R2 as well as 1/R terms (i.e. nonlinear contributions of the Ricci curvature with a non-analytic model of f(R) at R = 0) without considering any matter-dominated era. The terms with positive powers (1, 2) of the curvature support the inflationary epoch while the terms with negative power (-1) serves as effective dark energy, supporting current cosmic acceleration. We present a few analytical solutions of evolution equation for the deceleration parameter q as a function of Hubble parameter H and time t; specially in one solution, the universe evolves continuously from q = 1 (a radiation-dominated epoch) to q = -1/2 (dark-energy-dominated late-time accelerating phase) when the universe is sufficiently old. The solution is supported by numerical results. The transition from the decelerated (q > 0) to the accelerated phase (q < 0) of expansion takes place smoothly without having to resort to a study of asymptotic behavior.

scholarly journals EFFECTS OF CHERN–SIMONS CORRECTIONS ON CONSERVED QUANTITIES OF RELATIVISTIC FLUID

2010 ◽  
Vol 25 (31) ◽  
pp. 2655-2666
Author(s):  
KOHKICHI KONNO ◽  
TOYOKI MATSUYAMA ◽  
SATOSHI TANDA
Keyword(s):  
Fluid Flow ◽  
Modified Gravity ◽  
Gravity Theory ◽  
Conserved Quantities ◽  
Maxwell Theory ◽  
Relativistic Fluid ◽  
Modified Gravity Theory ◽  
Chern Simons

We consider relativistic fluid flow under Chern–Simons modified Maxwell theory and under Chern–Simons modified gravity theory. We take account of the effects of Chern–Simons corrections on the quantities of fluid flow that is conserved without the Chern–Simons corrections. We find that the conservations of several quantities are generally broken by the Chern–Simons corrections.

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