ON GENERATING SOME KNOWN BLACK HOLE SOLUTIONS

AbstractBlack holes represent outstanding astrophysical laboratories to test the strong gravity regime, since alternative theories of gravity may predict black hole solutions whose properties may differ distinctly from those of general relativity. When higher curvature terms are included in the gravitational action as, for instance, in the form of the Gauss–Bonnet term coupled to a scalar field, scalarized black holes result. Here we discuss several types of scalarized black holes and some of their properties.

Testing the Vainshtein mechanism using stars and galaxies

International Journal of Modern Physics D ◽

10.1142/s0218271815440216 ◽

2015 ◽

Vol 24 (12) ◽

pp. 1544021 ◽

Cited By ~ 8

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.

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

EPJ Web of Conferences ◽

10.1051/epjconf/201819101010 ◽

2018 ◽

Vol 191 ◽

pp. 01010 ◽

Cited By ~ 5

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.

On the black holes in alternative theories of gravity: The case of nonlinear massive gravity

International Journal of Modern Physics D ◽

10.1142/s0218271815500224 ◽

2015 ◽

Vol 24 (03) ◽

pp. 1550022 ◽

Cited By ~ 16

Author(s):

Ivan Arraut

Keyword(s):

Black Holes ◽

Black Hole ◽

Degrees Of Freedom ◽

Massive Gravity ◽

Alternative Theories Of Gravity ◽

De Sitter ◽

Theories Of Gravity ◽

Bound Orbits ◽

Black Hole Temperature ◽

Alternative Theories

I derive general conditions in order to explain the origin of the Vainshtein radius inside dRGT. The set of equations, which I have called "Vainshtein" conditions are extremal conditions of the dynamical metric (gμν) containing all the degrees of freedom of the theory. The Vainshtein conditions are able to explain the coincidence between the Vainshtein radius in dRGT and the scale [Formula: see text], obtained naturally from the Schwarzschild de-Sitter (S-dS) space inside general relativity (GR). In GR, this scale was interpreted as the maximum distance in order to get bound orbits. The same scale corresponds to the static observer position if we want to define the black hole temperature in an asymptotically de-Sitter space. In dRGT, the scale marks a limit after which the extra degrees of freedom of the theory become relevant.

The black hole at the Galactic Center: Observations and models

International Journal of Modern Physics D ◽

10.1142/s0218271818410092 ◽

2018 ◽

Vol 27 (06) ◽

pp. 1841009 ◽

Cited By ~ 12

Author(s):

Alexander F. Zakharov

Keyword(s):

Black Hole ◽

Theoretical Analysis ◽

Observational Data ◽

Galactic Center ◽

Massive Gravity ◽

Alternative Theories Of Gravity ◽

Graviton Mass ◽

Vlbi Observations ◽

Theories Of Gravity ◽

Alternative Theories

One of the most interesting astronomical objects is the Galactic Center. It is a subject of intensive astronomical observations in different spectral bands in recent years. We concentrate our discussion on a theoretical analysis of observational data of bright stars in the IR-band obtained with large telescopes. We also discuss the importance of VLBI observations of bright structures which could characterize the shadow at the Galactic Center. If we adopt general relativity (GR), there are a number of theoretical models for the Galactic Center, such as a cluster of neutron stars, boson stars, neutrino balls, etc. Some of these models were rejected or the range of their parameters is significantly constrained with consequent observations and theoretical analysis. In recent years, a number of alternative theories of gravity have been proposed because there are dark matter (DM) and dark energy (DE) problems. An alternative theory of gravity may be considered as one possible solution for such problems. Some of these theories have black hole solutions, while other theories have no such solutions. There are attempts to describe the Galactic Center with alternative theories of gravity and in this case one can constrain parameters of such theories with observational data for the Galactic Center. In particular, theories of massive gravity are intensively developing and theorists have overcome pathologies presented in the initial versions of these theories. In theories of massive gravity, a graviton is massive in contrast with GR where a graviton is massless. Now these theories are considered as an alternative to GR. For example, the LIGO–Virgo collaboration obtained the graviton mass constraint of about [Formula: see text] eV in their first publication about the discovery of the first gravitational wave detection event that resulted of the merger of two massive black holes. Surprisingly, one could obtain a consistent and comparable constraint of graviton mass at a level around [Formula: see text][Formula: see text]eV from the analysis of observational data on the trajectory of the star S2 near the Galactic Center. Therefore, observations of bright stars with existing and forthcoming telescopes such as the European extremely large telescope (E-ELT) and the thirty meter telescope (TMT) are extremely useful for investigating the structure of the Galactic Center in the framework of GR, but these observations also give a tool to confirm, rule out or constrain alternative theories of gravity. As we noted earlier, VLBI observations with current and forthcoming global networks (like the Event Horizon Telescope) are used to check the hypothesis about the presence of a supermassive black hole at the Galactic Center.

FOURTH-ORDER GRAVITY AND EXPERIMENTAL CONSTRAINTS ON EDDINGTON PARAMETERS

Modern Physics Letters A ◽

10.1142/s0217732306021633 ◽

2006 ◽

Vol 21 (30) ◽

pp. 2291-2301 ◽

Cited By ~ 58

Author(s):

S. CAPOZZIELLO ◽

A. STABILE ◽

A. TROISI

Keyword(s):

Experimental Data ◽

General Relativity ◽

Alternative Theories Of Gravity ◽

Third Order ◽

Definitive Answer ◽

Order Polynomial ◽

Theories Of Gravity ◽

Definition Of ◽

Ppn Parameters ◽

Alternative Theories

PPN-limit of alternative theories of gravity represents a still controversial matter of debate and no definitive answer has been provided, up to now, about this issue. By using the definition of the PPN-parameters γ and β in terms of f(R) theories of gravity, we show that a family of third-order polynomial theories, in the Ricci scalar R, turns out to be compatible with the PPN-limit and the deviation from General Relativity, theoretically predicted, can agree with experimental data.

Renormalizability of Alternative Theories of Gravity: Differences between Power Counting and Entropy Argument

Universe ◽

10.3390/universe7050148 ◽

2021 ◽

Vol 7 (5) ◽

pp. 148

Author(s):

Francesco Bajardi ◽

Francesco Bascone ◽

Salvatore Capozziello

Keyword(s):

General Relativity ◽

Teleparallel Gravity ◽

Power Counting ◽

Alternative Theories Of Gravity ◽

Spherically Symmetric ◽

Asymptotic Safety ◽

Renormalizable Theory ◽

Theories Of Gravity ◽

Working Out ◽

Alternative Theories

It is well known that General Relativity cannot be considered under the standard of a perturbatively renormalizable quantum field theory, but asymptotic safety is taken into account as a possibility for the formulation of gravity as a non-perturbative renormalizable theory. Recently, the entropy argument has however stepped into the discussion claiming for a “no-go” to the asymptotic safety argument. In this paper, we present simple counter-examples, considering alternative theories of gravity, to the entropy argument as further indications, among others, on the possible flows in the assumptions on which the latter is based. We considered different theories, namely curvature-based extensions of General Relativity as f(R), f(G), extensions of teleparallel gravity as f(T), and Horava–Lifshitz gravity, working out the explicit spherically symmetric solutions in order to make a comparison between power counting and the entropy argument. Even in these cases, inconsistencies were found.

Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities

Contributions of the Astronomical Observatory Skalnaté Pleso ◽

10.31577/caosp.2020.50.1.203 ◽

2020 ◽

Vol 50 (1) ◽

Author(s):

A.F. Zakharov ◽

P. Jovanović ◽

D. Borka ◽

V. Borka Jovanović

Keyword(s):

General Relativity ◽

Galactic Center ◽

Alternative Theories Of Gravity ◽

Tests Of General Relativity ◽

Theories Of Gravity ◽

Alternative Theories

TESTS OF GENERAL RELATIVITY AND ALTERNATIVE THEORIES OF GRAVITY USING GRAVITATIONAL WAVE OBSERVATIONS

International Journal of Modern Physics D ◽

10.1142/s0218271813410125 ◽

2013 ◽

Vol 22 (01) ◽

pp. 1341012 ◽

Cited By ~ 17

Author(s):

K. G. ARUN ◽

ARCHANA PAI

Keyword(s):

General Relativity ◽

Gravitational Wave ◽

Strong Field ◽

Information Matrix ◽

Simons Theory ◽

Alternative Theories Of Gravity ◽

Newtonian Theory ◽

Theories Of Gravity ◽

Model Independent ◽

Alternative Theories

Gravitational wave (GW) observations of coalescing compact binaries will be unique probes of strong-field, dynamical aspects of relativistic gravity. We present a short review of various schemes proposed in the literature to test general relativity (GR) and alternative theories of gravity using inspiral waveforms. Broadly these schemes may be classified into two types: model dependent and model independent. In the model dependent category, GW observations are compared against a specific waveform model representative of a particular theory or a class of theories such as scalar-tensor theories, dynamical Chern–Simons theory and massive graviton theories. Model independent tests are attempts to write down a parametrized gravitational waveform where the free parameters take different values for different theories and (at least some of) which can be constrained by GW observations. We revisit some of the proposed bounds in the case of downscaled LISA configuration (eLISA) and compare them with the original LISA configuration. We also compare the expected bounds on alternative theories of gravity from ground-based and space-based detectors and find that space-based GW detectors can test GR and other theories of gravity with unprecedented accuracies. We then focus on a recent proposal to use singular value decomposition of the Fisher information matrix to improve the accuracies with which post-Newtonian theory can be tested. We extend those results to the case of space-based detector eLISA and discuss its implications.

Radioscience simulations in general relativity and in alternative theories of gravity

Classical and Quantum Gravity ◽

10.1088/0264-9381/29/23/235027 ◽

2012 ◽

Vol 29 (23) ◽

pp. 235027 ◽

Cited By ~ 32

Author(s):

A Hees ◽

B Lamine ◽

S Reynaud ◽

M-T Jaekel ◽

C Le Poncin-Lafitte ◽

...

Keyword(s):

General Relativity ◽

Alternative Theories Of Gravity ◽

Theories Of Gravity ◽

Alternative Theories