Dark matter and dark energy or alternative theories of gravity and cosmology

2008 ◽  
Author(s):  
Alexander F. Zakharov ◽  
Victor N. Pervushin ◽  
Francesco De Paolis ◽  
Gabriele Ingrosso ◽  
Achille A. Nucita ◽  
...  
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Alternative Theories Of Gravity ◽  
Theories Of Gravity ◽  
Alternative Theories

scholarly journals Testing the Vainshtein mechanism using stars and galaxies

2015 ◽  
Vol 24 (12) ◽  
pp. 1544021 ◽  
Author(s):  
Jeremy Sakstein ◽  
Kazuya Koyama
Keyword(s):  
General Relativity ◽  
Solar System ◽  
Main Sequence ◽  
Alternative Theories Of Gravity ◽  
The Novel ◽  
Main Sequence Stars ◽  
Cosmic Expansion ◽  
Astrophysical Objects ◽  
Theories Of Gravity ◽  
Alternative Theories

The Vainshtein mechanism is of paramount importance in many alternative theories of gravity. It hides deviations from general relativity (GR) in the solar system while allowing them to drive the acceleration of the cosmic expansion. Recently, a class of theories have emerged where the mechanism is broken inside astrophysical objects. In this essay, we look for novel probes of these theories by deriving the modified properties of stars and galaxies. We show that main-sequence stars are colder, less luminous and more ephemeral than GR predicts. Furthermore, the circular velocities of objects orbiting inside galaxies are slower and the lensing of light is weaker. We discuss the prospects for testing these theories using the novel phenomena presented here in light of current astrophysical surveys.

scholarly journals Constraints on alternative theories of gravity with observations of the Galactic Center

2018 ◽  
Vol 191 ◽  
pp. 01010 ◽  
Author(s):  
Alexander Zakharov
Keyword(s):  
Black Hole ◽  
Gravitational Wave ◽  
Galactic Center ◽  
Alternative Theories Of Gravity ◽  
Significant Activity ◽  
Graviton Mass ◽  
The Future ◽  
Theories Of Gravity ◽  
Theory Of Gravity ◽  
Alternative Theories

To evaluate a potential usually one analyzes trajectories of test particles. For the Galactic Center case astronomers use bright stars or photons, so there are two basic observational techniques to investigate a gravitational potential, namely, (a) monitoring the orbits of bright stars near the Galactic Center as it is going on with 10m Keck twin and four 8m VLT telescopes equipped with adaptive optics facilities (in addition, recently the IR interferometer GRAVITY started to operate with VLT); (b) measuring the size and shape of shadows around black hole with VLBI-technique using telescopes operating in mm-band. At the moment, one can use a small relativistic correction approach for stellar orbit analysis, however, in the future the approximation will not be precise enough due to enormous progress of observational facilities and recently the GRAVITY team found that the first post-Newtonian correction has to be taken into account for the gravitational redshift in the S2 star orbit case. Meanwhile for smallest structure analysis in VLBI observations one really needs a strong gravitational field approximation. We discuss results of observations and their interpretations. In spite of great efforts there is a very slow progress to resolve dark matter (DM) and dark energy (DE) puzzles and in these circumstances in last years a number of alternative theories of gravity have been proposed. Parameters of these theories could be effectively constrained with of observations of the Galactic Center. We show some cases of alternative theories of gravity where their parameters are constrained with observations, in particular, we consider massive theory of gravity. We choose the alternative theory of gravity since there is a significant activity in this field and in the last years theorists demonstrated an opportunity to create such theories without ghosts, on the other hand, recently, the joint LIGO & Virgo team presented an upper limit on graviton mass such as mg< 1:2 × 10-22eV [1] analyzing gravitational wave signal in their first paper where they reported about the discovery of gravitational waves from binary black holes as it was suggested by C. Will [2]. So, the authors concluded that their observational data do not indicate a significant deviation from classical general relativity. We show that an analysis of bright star trajectories could estimate a graviton mass with a commensurable accuracy in comparison with an approach used in gravitational wave observations and the estimates obtained with these two approaches are consistent. Therefore, such an analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a useful tool to obtain constraints on the fundamental gravity law. We showed that in the future graviton mass estimates obtained with analysis of trajectories of bright stars would be better than current LIGO bounds on the value, therefore, based on a potential reconstruction at the Galactic Center we obtain bounds on a graviton mass and these bounds are comparable with LIGO constraints. Analyzing size of shadows around the supermassive black hole at the Galactic Center (or/and in the center of M87) one could constrain parameters of different alternative theories of gravity as well.

scholarly journals Cosmological production of black holes: A way to constrain alternative theories of gravity

2018 ◽  
Vol 97 (12) ◽  
Author(s):  
Konstantinos F. Dialektopoulos ◽  
Antonios Nathanail ◽  
Athanasios G. Tzikas
Keyword(s):  
Black Holes ◽  
Alternative Theories Of Gravity ◽  
Theories Of Gravity ◽  
Alternative Theories

PRECISION TESTS OF THEORIES OF GRAVITY USING PULSARS

2014 ◽  
Vol 23 (03) ◽  
pp. 1430004 ◽  
Author(s):  
MICHAEL KRAMER
Keyword(s):  
Scalar Fields ◽  
Alternative Theories Of Gravity ◽  
Dipole Radiation ◽  
Geodetic Precession ◽  
Gravity Effects ◽  
Theories Of Gravity ◽  
Orbital Precession ◽  
Tests Of Gravity ◽  
Alternative Theories ◽  
Strong Equivalence Principle

In the quest of understanding gravity, binary pulsars provide indispensable laboratories for precision tests of gravity. Effects that can be studied in great detail include the emission of gravitational waves, Shapiro delay, orbital precession and more. But also fundamental differences between general relativity and alternative theories of gravity can be probed, such as possible violations of the strong equivalence principle, preferred frame effects or the existence of gravitational dipole radiation or scalar fields. Also the effects of spin precession in strongly self-gravitating bodies can be studied by observing effects of geodetic precession.

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