scholarly journals Modified Gravity and Dark Matter

2021 ◽  
Author(s):  
Syed Abbas ◽  
Nasim Akhtar ◽  
Danish Alam
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Quantum Mechanics ◽  
Modified Gravity ◽  
Gravitational Force ◽  
Relativistic Quantum ◽  
The Other ◽  
Gravitational Mass ◽  
Galilei Group ◽  
The Universe

At present there is a renewed interest in theories of ”modified” gravity. Here, under a more drastic modification enforced by Galilei group, we obtain a completely new gravitational structure, and which exists in addition to the already available general relativity of today. Correlated with this, we show that in addition, there is a new ”modified” quantum mechanics, in as much as it exists as an independent and new ”pure” non-relativistic quantum me- chanics, and which has no relativistic counterpart. This is in addition to the present quantum mechanics, where the relativistic and non-relativistic structures are counterparts of each other. The above holds, firstly due to the correlation between Galilei group and quantum mechanics. These math- ematical conclusions are consolidated by the fact that there exists a physical Majorana interaction between each neutron- proton pairs in nuclei. Galilei invariance of Majorana exchange in Majorana interaction, shows that the mass here is of pure gravitational nature, and which is immune to the other three forces. This makes an amazing connection between the gravitational force and the quantum mechanics. This pure gravitational mass would man- ifest itself as dark matter of the universe. It is our new modified gravity that generates the dark matter.

HALOS OF MODIFIED GRAVITY

2008 ◽  
Vol 17 (13n14) ◽  
pp. 2555-2562 ◽  
Author(s):  
KIRILL KRASNOV ◽  
YURI SHTANOV
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Cosmological Constant ◽  
Modified Gravity ◽  
Alternative Explanation ◽  
Gravitational Mass ◽  
Spherically Symmetric ◽  
Simple Modification ◽  
Type Ia ◽  
Supernova Type Ia

We describe how a certain simple modification of general relativity, in which the local cosmological constant is allowed to depend on the space–time curvature, predicts the existence of halos of modified gravity surrounding spherically symmetric objects. We show that the gravitational mass of an object weighed together with its halo can be much larger than its gravitational mass as seen from inside the halo. This effect could provide an alternative explanation of the dark-matter phenomenon in galaxies. In this case, the local cosmological constant in the solar system must be some six orders of magnitude larger than its cosmic value obtained in the supernova type Ia experiments. This is well within the current experimental bounds, but may be directly observable in future high-precision experiments.

Dark matter (energy) may be indistinguishable from modified gravity (MOND)

2017 ◽  
Vol 26 (12) ◽  
pp. 1743010 ◽  
Author(s):  
C. Sivaram
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Dark Energy ◽  
Modified Gravity ◽  
Observational Evidence ◽  
Negative Results ◽  
Newtonian Dynamics ◽  
Special Cases ◽  
The Universe ◽  
Matter Energy

For Newtonian dynamics to hold over galactic scales, large amounts of dark matter (DM) are required which would dominate cosmic structures. Accounting for the strong observational evidence that the universe is accelerating requires the presence of an unknown dark energy (DE) component constituting about 70% of the matter. Several ingenious ongoing experiments to detect the DM particles have so far led to negative results. Moreover, the comparable proportions of the DM and DE at the present epoch appear unnatural and not predicted by any theory. For these reasons, alternative ideas like MOND and modification of gravity or general relativity over cosmic scales have been proposed. It is shown in this paper that these alternate ideas may not be easily distinguishable from the usual DM or DE hypotheses. Specific examples are given to illustrate this point that the modified theories are special cases of a generalized DM paradigm.

scholarly journals R2-Cosmology and New Windows for Superheavy Dark Matter

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 877
Author(s):  
Elena Arbuzova ◽  
Alexander Dolgov ◽  
Rajnish Singh
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Modified Gravity ◽  
Gauge Bosons ◽  
Decay Channels ◽  
Decay Modes ◽  
The Masses ◽  
Superheavy Dark Matter ◽  
The Universe

Evolution and heating of the universe in R2-modified gravity are considered. It is shown that the universe’s history can be separated into four different epochs: (1) inflation, (2) heating due to curvature oscillations (scalaron decay), (3) transition to matter dominated period, and (4) conventional cosmology governed by General Relativity. Cosmological density of dark matter (DM) particles for different decay channels of the scalaron is calculated. The bounds on the masses of DM particles are derived for the following dominant decay modes: to minimally coupled scalars, to massive fermions, and to gauge bosons.

scholarly journals The connection between halo concentrations and assembly histories: a probe of gravity?

2019 ◽  
Vol 489 (4) ◽  
pp. 4658-4668
Author(s):  
Piotr Oleśkiewicz ◽  
Carlton M Baugh ◽  
Aaron D Ludlow
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
High Resolution ◽  
Modified Gravity ◽  
Mass Concentration ◽  
The Other ◽  
Formation Time ◽  
Density Profiles ◽  
Time Relation ◽  
Halo Population

ABSTRACT We use two high-resolution N-body simulations, one assuming general relativity (GR) and the other the Hu–Sawicki form of f(R) gravity with $\vert \bar{f}_{\mathrm{ R}} \vert = 10^{-6}$, to investigate the concentration–formation time relation of dark matter haloes. We assign haloes to logarithmically spaced mass bins, and fit median density profiles and extract median formation times in each bin. At fixed mass, haloes in modified gravity are more concentrated than those in GR, especially at low masses and low redshift, and do not follow the concentration–formation time relation seen in GR. We assess the sensitivity of the relation to how concentration and formation time are defined, as well as to the segregation of the halo population by the amount of gravitational screening. We find a clear difference between halo concentrations and assembly histories displayed in modified gravity and those in GR. Existing models for the mass–concentration–redshift relation that have gained success in cold and warm dark matter models require revision in f(R) gravity.

GRAVITY CAN BE OBSERVED IN THE ABSENCE OF CURVED SPACETIME, THUS CURVED SPACETIME IS NOT RESPONCIBLE FOR GRAVITY

2015 ◽  
Vol 8 (1) ◽  
pp. 1976-1981
Author(s):  
Casey McMahon
Keyword(s):  
General Relativity ◽  
Special Relativity ◽  
Relative Position ◽  
Gravitational Force ◽  
Curved Spacetime ◽  
Relative Time ◽  
Curved Space ◽  
Spacetime Curvature ◽  
Equivalence Model ◽  
The Universe

The principle postulate of general relativity appears to be that curved space or curved spacetime is gravitational, in that mass curves the spacetime around it, and that this curved spacetime acts on mass in a manner we call gravity. Here, I use the theory of special relativity to show that curved spacetime can be non-gravitational, by showing that curve-linear space or curved spacetime can be observed without exerting a gravitational force on mass to induce motion- as well as showing gravity can be observed without spacetime curvature. This is done using the principles of special relativity in accordance with Einstein to satisfy the reader, using a gravitational equivalence model. Curved spacetime may appear to affect the apparent relative position and dimensions of a mass, as well as the relative time experienced by a mass, but it does not exert gravitational force (gravity) on mass. Thus, this paper explains why there appears to be more gravity in the universe than mass to account for it, because gravity is not the resultant of the curvature of spacetime on mass, thus the “dark matter” and “dark energy” we are looking for to explain this excess gravity doesn’t exist.

scholarly journals Neutron stars as probes of dark matter

2020 ◽  
Vol 29 (14) ◽  
pp. 2043028
Author(s):  
M. Ángeles Pérez-García ◽  
Joseph Silk
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Equation Of State ◽  
Neutron Stars ◽  
Internal Structure ◽  
Stellar Objects ◽  
Ordinary Matter ◽  
Stable Solutions ◽  
The Universe

Neutron Stars (NSs) are compact stellar objects that are stable solutions in General Relativity. Their internal structure is usually described using an equation of state that involves the presence of ordinary matter and its interactions. However there is now a large consensus that an elusive sector of matter in the universe, described as dark matter, remains as yet undiscovered. In such a case, NSs should contain both, baryonic and dark matter. We argue that depending on the nature of the dark matter and in certain circumstances, the two matter components would form a mixture inside NSs that could trigger further changes, some of them observable. The very existence of NSs constrains the nature and interactions of dark matter in the universe.

scholarly journals Gravity as entanglement, entanglement as gravity

2020 ◽  
Author(s):  
Vasil Dinev Penchev
Keyword(s):  
General Relativity ◽  
Quantum Mechanics ◽  
Reference Frame ◽  
Common Sense ◽  
Reference Frames ◽  
General Covariance ◽  
The Universe

A generalized and unifying viewpoint to both general relativity and quantum mechanics and information is investigated. It may be described as a generaliztion of the concept of reference frame from mechanics to thermodynamics, or from a reference frame linked to an element of a system, and thus, within it, to another reference frame linked to the whole of the system or to any of other similar systems, and thus, out of it. Furthermore, the former is the viewpoint of general relativity, the latter is that of quantum mechanics and information.Ciclicity in the manner of Nicolas Cusanus (Nicolas of Cusa) is complemented as a fundamental and definitive property of any totality, e.g. physically, that of the universe. It has to contain its externality within it somehow being namely the totality. This implies a seemingly paradoxical (in fact, only to common sense rather logically and mathematically) viewpoint for the universe to be repesented within it as each one quant of action according to the fundamental Planck constant.That approach implies the unification of gravity and entanglement correspondiing to the former or latter class of reference frames. An invariance, more general than Einstein's general covariance is to be involved as to both classes of reference frames unifying them. Its essence is the unification of the discrete and cotnitinuous (smooth). That idea underlies implicitly quantum mechanics for Bohr's principle that it study the system of quantum microscopic entities and the macroscopic apparatus desribed uniformly by the smmoth equations of classical physics.e

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 On galaxy rotation curves from a continuum mechanics approach to modified gravity

2018 ◽  
Vol 27 (02) ◽  
pp. 1850007 ◽  
Author(s):  
Christian G. Böhmer ◽  
Nicola Tamanini ◽  
Matthew Wright
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Continuum Mechanics ◽  
Modified Gravity ◽  
Galactic Rotation ◽  
Dark Matter Halos ◽  
Additional Structure ◽  
Rotation Curves ◽  
Small Deviations ◽  
Galaxy Rotation Curves

We consider a modification of General Relativity motivated by the treatment of anisotropies in Continuum Mechanics. The Newtonian limit of the theory is formulated and applied to galactic rotation curves. By assuming that the additional structure of spacetime behaves like a Newtonian gravitational potential for small deviations from isotropy, we are able to recover the Navarro–Frenk–White profile of dark matter halos by a suitable identification of constants. We consider the Burkert profile in the context of our model and also discuss rotation curves more generally.

Massive particles, Kerr–Minkowski fields and singularity removal in relativistic quantum mechanics

2007 ◽  
Vol 463 (2083) ◽  
pp. 1815-1826
Author(s):  
Brian Bramson
Keyword(s):  
General Relativity ◽  
Quantum Mechanics ◽  
Relativistic Quantum ◽  
Radial Distance ◽  
Unitary Representations ◽  
Relativistic Quantum Mechanics ◽  
Twistor Theory ◽  
Kerr Field ◽  
Singularity Removal ◽  
Bounded Below

This paper concerns the spacetime locations of massive spinning particles in relativistic quantum mechanics. Using techniques from twistor theory and the unitary representations of the Lorentz group, it is shown that, for a particle of mass m and spin j , the radial distance from the particle to the observer is bounded below by . If the particle is the source of a Kerr–Minkowski field, the analogue of a Kerr field in general relativity, it is further shown that quantization removes the ring singularity if j is Fermionic or zero.

Sign in / Sign up

Export Citation Format

Share Document