Particle production in modified gravity in the early and present day universe

2020 ◽  
Vol 35 (36) ◽  
pp. 2044027
Author(s):  
E. V. Arbuzova
Keyword(s):  
Dark Matter ◽  
Energy Spectrum ◽  
Cosmic Rays ◽  
Modified Gravity ◽  
Particle Production ◽  
Equations Of Motion ◽  
Modified Theories Of Gravity ◽  
Oscillating Solutions ◽  
Theories Of Gravity ◽  
Gravitational Equations

Gravitational equations of motion in modified theories of gravity have oscillating solutions, both in the early and in the present day universe. Particle production by such oscillations is analyzed and possible observational consequences are considered. This phenomenon has impact on energy spectrum of cosmic rays and abundance of dark matter particles.

On Modified Gravity

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Viktor Toth ◽  
Jean-Pierre Luminet
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Modified Theories Of Gravity ◽  
Theories Of Gravity

Viktor Toth adds theoretical insights to the modified theories of gravity that aimed to solve the dark matter problem without necessitating the existence of hypothetic particles of nonbaryonic matter.

scholarly journals Giant low-surface-brightness dwarf galaxy as a test bench for MOdified Gravity

2020 ◽  
Vol 493 (2) ◽  
pp. 2373-2376 ◽  
Author(s):  
Ivan de Martino
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Dwarf Galaxy ◽  
Weak Field ◽  
Newtonian Potential ◽  
Modified Theories Of Gravity ◽  
Weak Field Limit ◽  
Low Surface Brightness ◽  
Standard Cosmological Model ◽  
Theories Of Gravity

ABSTRACT The lack of detection of supersymmetric particles is leading to look at alternative avenues for explaining dark matter’s effects. Among them, modified theories of gravity may play an important role accounting even for both dark components needed in the standard cosmological model. Scalar–tensor–vector gravity theory has been proposed to resolve the dark matter puzzle. Such a modified gravity model introduces, in its weak field limit, a Yukawa-like correction to the Newtonian potential, and is capable to explain most of the phenomenology related to dark matter at scale of galaxies and galaxy clusters. Nevertheless, some inconsistencies appear when studying systems that are supposed to be dark matter dominated such as dwarf galaxies. In this sense, Antlia II, an extremely diffuse galaxy which has been recently discovered in Gaia’s second data release, may serve to probe the aforementioned theory against the need for invoking dark matter. Our analysis shows several inconsistencies and leads to argue that MOdified Gravity may not be able to shed light on the intriguing nature of dark matter.

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 Higher-derivative f(R,□R,T) theories of gravity

2017 ◽  
Vol 26 (03) ◽  
pp. 1750024 ◽  
Author(s):  
M. J. S. Houndjo ◽  
M. E. Rodrigues ◽  
N. S. Mazhari ◽  
D. Momeni ◽  
R. Myrzakulov
Keyword(s):  
Modified Gravity ◽  
Equations Of Motion ◽  
Momentum Tensor ◽  
De Sitter ◽  
Higher Derivative ◽  
Stress Energy ◽  
Derivative Term ◽  
Theories Of Gravity ◽  
Tensor Formula ◽  
Stress Energy Momentum Tensor

In literature, there is a model of modified gravity in which the matter Lagrangian is coupled to the geometry via trace of the stress–energy–momentum tensor [Formula: see text]. This type of modified gravity is denoted [Formula: see text] in which [Formula: see text] is Ricci scalar [Formula: see text]. We extend manifestly this model to include the higher derivative term [Formula: see text]. We derived equations of motion (EOM) for the model by starting from the basic variational principle. Later we investigate FLRW cosmology for our model. We show that de Sitter (dS) solution is unstable for a generic type of [Formula: see text] model. Furthermore we investigate an inflationary scenario based on this model. A graceful exit from inflation is guaranteed in this type of modified gravity.

scholarly journals PALATINI FORMULATION OF MODIFIED GRAVITY WITH A NON-MINIMAL CURVATURE-MATTER COUPLING

2011 ◽  
Vol 26 (20) ◽  
pp. 1467-1480 ◽  
Author(s):  
TIBERIU HARKO ◽  
TOMI S. KOIVISTO ◽  
FRANCISCO S. N. LOBO
Keyword(s):  
Energy Momentum Tensor ◽  
Equations Of Motion ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
Nonlinear Dependence ◽  
Modified Theories Of Gravity ◽  
Field Equations ◽  
Test Particles ◽  
Theories Of Gravity ◽  
Minimal Curvature

We derive the field equations and the equations of motion for scalar fields and massive test particles in modified theories of gravity with an arbitrary coupling between geometry and matter by using the Palatini formalism. We show that the independent connection can be expressed as the Levi–Cività connection of an auxiliary, matter Lagrangian dependent metric, which is related with the physical metric by means of a conformal transformation. Similarly to the metric case, the field equations impose the nonconservation of the energy–momentum tensor. We derive the explicit form of the equations of motion for massive test particles in the case of a perfect fluid, and the expression of the extra-force is obtained in terms of the matter-geometry coupling functions and of their derivatives. Generally, the motion is non-geodesic, and the extra force is orthogonal to the four-velocity. It is pointed out here that the force is of a different nature than in the metric formalism. We also consider the implications of a nonlinear dependence of the action upon the matter Lagrangian.

scholarly journals Causal hierarchy in modified gravity

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Raúl Carballo-Rubio ◽  
Francesco Di Filippo ◽  
Stefano Liberati ◽  
Matt Visser
Keyword(s):  
Modified Gravity ◽  
Modified Theories Of Gravity ◽  
Global Hyperbolicity ◽  
Signal Velocity ◽  
Superluminal Propagation ◽  
Strong Causality ◽  
Theories Of Gravity ◽  
Stable Causality ◽  
Multiple Metrics ◽  
Extra Structure

Abstract We investigate the causal hierarchy in various modified theories of gravity. In general relativity the standard causal hierarchy, (key elements of which are chronology, causality, strong causality, stable causality, and global hyperbolicity), is well-established. In modified theories of gravity there is typically considerable extra structure, (such as: multiple metrics, aether fields, modified dispersion relations, Hořava-like gravity, parabolic propagation, etcetera), requiring a reassessment and rephrasing of the usual causal hierarchy. We shall show that in this extended framework suitable causal hierarchies can indeed be established, and discuss the implications for the interplay between “superluminal” propagation and causality. The key distinguishing feature is whether the signal velocity is finite or infinite. Preserving even minimal notions of causality in the presence of infinite signal velocity requires the aether field to be both unique and hypersurface orthogonal, leading us to introduce the notion of global parabolicity.

scholarly journals INFLATION IN F(R, T) GRAVITATION WITH f-ESSENCE

2020 ◽  
Vol 5 (333) ◽  
pp. 106-112
Author(s):  
S.R. Myrzakul ◽  
◽  
Y.M. Myrzakulov ◽  
М. Arzimbetova ◽  
◽  
...  
Keyword(s):  
Equations Of Motion ◽  
Accelerated Expansion ◽  
Modified Theories Of Gravity ◽  
Fermion Field ◽  
Theory Of Relativity ◽  
Modern Physics ◽  
Expansion Of The Universe ◽  
Isotropic Cosmological Model ◽  
Theories Of Gravity ◽  
The Universe

. Modified theories of gravity have become a kind of paradigm in modern physics because they seem to solve several shortcomings of the standard General Theory of Relativity (GTR) related to cosmology, astrophysics and quantum field theory. The most famous modified theories of gravity are F(R) and F(T) theories of gravity. A generalization of these two modified theories and gravitations, which was first proposed by Myrzakulov Ratbay. In this paper, we study an inhomogeneous isotropic cosmological model with a fermion field f-essence whose action has the form , where R is the scalar of curvature, and T is the torsion scalar, and Lm is the Lagrangian f-essence. A particular case is studied in detail when parameters are obtained that describe the current accelerated expansion of the Universe. The type of Lagrangian f-essence of this model is determined. The presented results show that gravity with f-essence can describe inflation in the early evolution of the Universe. A modified F(R, T) gravity with f-essence is considered. Equations of motion were obtained and the inflationary period of the early Universe was considered. To describe the inflationary period, the form of the Hubble parameter and the slow-roll parameter were determined.

A primer on modified gravity

2019 ◽  
Vol 28 (05) ◽  
pp. 1942004 ◽  
Author(s):  
Radouane Gannouji
Keyword(s):  
General Relativity ◽  
Modified Gravity ◽  
Alternative Model ◽  
Modified Theories Of Gravity ◽  
Observational Constraints ◽  
Special Issue ◽  
Consistent Model ◽  
Theories Of Gravity

In this first chapter of the Special Issue on Modified Theories of Gravity and Constraints Imposed by Recent GW Observations, we review observational constraints on gravity and the possibility to construct an alternative model to general relativity. For that, we motivate the study of theories beyond Einstein’s gravity, some of their phenomenology and the various ingredients to build a consistent model.

scholarly journals Non-Detection of Dark Matter Particles: A Case for Alternate Theories of Gravity

2020 ◽  
Author(s):  
Arun Kenath ◽  
C Sivaram ◽  
Avijeet Prasad ◽  
Louise Rebecca
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Modified Gravity ◽  
Newtonian Gravity ◽  
Self Energy ◽  
Overwhelming Evidence ◽  
Modified Equations ◽  
Modified Gravity Theories ◽  
Flat Rotation Curves ◽  
Theories Of Gravity

While there is overwhelming evidence for dark matter (DM) in galaxies and galaxy clusters, all searches for DM particles have so far proved negative. It is not even clear whether only one particle is involved or a combination or particles, their masses not precisely predicted. This non-detectability raises the possible relevance of modified gravity theories – MOND, MONG, etc. Here we consider a specific modification of Newtonian gravity (MONG) which involves gravitational self-energy, leading to modified equations whose solutions imply flat rotation curves and limitations of sizes of clusters. The results are consistent with current observations including that involving large spirals. This modification could also explain the current Hubble tension. We also consider effects of dark energy (DE) in terms of a cosmological constant.

scholarly journals Proton energy spectrum with the DAMPE experiment

2019 ◽  
Vol 209 ◽  
pp. 01030 ◽  
Author(s):  
Antonio De Benedittis
Keyword(s):  
Dark Matter ◽  
Energy Spectrum ◽  
Cosmic Rays ◽  
Kinetic Energy ◽  
Elemental Composition ◽  
Proton Energy ◽  
Dark Matter Particle ◽  
Space Mission ◽  
Galactic Cosmic Rays ◽  
Proton Energy Spectrum

The DAMPE (DArk Matter Particle Explorer) experiment, in orbit since December 17th 2015, is a space mission whose main purpose is the detection of cosmic electrons and photons up to energies of 10 TeV, in order to identify possible evidence of Dark Matter in their spectra. Furthermore it aims to measure the spectra and the elemental composition of the galactic cosmic rays nuclei up to the energy of hundreds of TeV. The proton analysis and the flux with kinetic energy ranging from 50 GeV up to 100 TeV, at the end of two years of data taking, will be presented and discussed.

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