Relativistic Cosmology, Numerical Analysis, General Relativity and Modified Gravity Theories

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 10290

Special Issue Editors


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Department of Mathematics, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
Interests: mathematical physics; geometry; stellar dynamics; self-gravitating systems; gravitational theories
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
Department of Mathematics, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
Interests: geometry; nonlinear analysis; theoretical and mathematical physics; relativistic astrophysics; cosmology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue welcomes original research articles that focus on the analysis of astrophysical objects in the context of Extended Gravity Theories. We also welcome the paper related to numerical simulations of linear and non-linear dynamical systems. We are hoping to attract studies regarding the possible attainment of high masses of neutron stars and white dwarfs from the Extended Gravity Theories perspective. Moreover, the question of whether it is possible to obtain nonexotic matter wormhole solutions in these theories is expected to be addressed. The physical consequences of studying black holes, strange stars, and gravastars in Extended Gravity Theories are also welcome. The purpose of this special issue is to compile original findings with an emphasis on numerical and theoretical challenges in dynamical systems. Review articles on the current state of the art are also invited.

Traditional formulations or more recent methods based on compartmental models, dynamic networking systems, multi-scale problems, linear and nonlinear differential equations, fractional differential equations and Hamiltonian dynamic evolutions are all welcome. We also expect to receive review articles describing the current state-of-the-art within this broad subject. Potential topics include but are not limited to the following:

Astrophysics and Astroparticle Physics

Astronomical observations; cosmological implications of the God particle; dark matter astrophysics; dark energy; electromagnetic process and properties; fundamental aspects of astrophysics; high-energy astrophysics/astroparticle; relativistic stars, structure, stability and oscillation—other topics.

Cosmology

Cosmic acceleration; cosmic microwave background radiation; inhomogeneous exact cosmologies; large scale structures; mathematical and relativistic aspects of cosmology; observational cosmology including the Hubble constant, distance scale, cosmological constant, early universe; theoretical cosmology—other topics.

Compact Objects

Black holes, mergers and accretion disks; galaxy evolution; measurements common to several branches of physics and astronomy; neutron stars; self-gravitating systems; strong gravitational lensing—other topics.

General Relativity and Modified Gravity Theories

Alternative theories of gravity; classical general relativity; numerical studies of critical behavior, singularities and cosmic censorship; strong-field tests of general relativity—other topics.

Non-linear Analysis

Non-linear analysis in mathematics, physics, biologychemistryengineering, economicshistory, and medicine; dynamical systems; linear dynamic system; nonlinear dynamic system; theoretical challenges in differetial calculus; numerical methods; fractional differential equations.

Dr. Zeeshan Yousaf
Dr. Kazuharu Bamba
Dr. M. Z. Bhatti
Guest Editors

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Keywords

  • astrophysics and astroparticle physics
  • cosmology
  • compact objects
  • general relativity and modified gravity theories

Published Papers (4 papers)

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Research

11 pages, 296 KiB  
Article
On the Periodic Orbits of the Perturbed Two- and Three-Body Problems
by Elbaz I. Abouelmagd, Juan Luis García Guirao and Jaume Llibre
Galaxies 2023, 11(2), 58; https://doi.org/10.3390/galaxies11020058 - 18 Apr 2023
Cited by 3 | Viewed by 1354
Abstract
In this work, a perturbed system of the restricted three-body problem is derived when the perturbation forces are conservative alongside the corresponding mean motion of two primaries bodies. Thus, we have proved that the first and second types of periodic orbits of the [...] Read more.
In this work, a perturbed system of the restricted three-body problem is derived when the perturbation forces are conservative alongside the corresponding mean motion of two primaries bodies. Thus, we have proved that the first and second types of periodic orbits of the rotating Kepler problem can persist for all perturbed two-body and circular restricted three-body problems when the perturbation forces are conservative or the perturbed motion has its own extended Jacobian integral. Full article
17 pages, 538 KiB  
Article
The Simplest Parametrization of the Equation of State Parameter in the Scalar Field Universe
by Preeti Shrivastava, Abdul Junaid Khan, Mukesh Kumar, Gopikant Goswami, Jainendra Kumar Singh and Anil Kumar Yadav
Galaxies 2023, 11(2), 57; https://doi.org/10.3390/galaxies11020057 - 17 Apr 2023
Cited by 10 | Viewed by 1501
Abstract
In this paper, we investigate a scalar field cosmological model of accelerating Universe with the simplest parametrization of the equation of state parameter of the scalar field. We use H(z) data, pantheon compilation of SN Ia data and BAO data [...] Read more.
In this paper, we investigate a scalar field cosmological model of accelerating Universe with the simplest parametrization of the equation of state parameter of the scalar field. We use H(z) data, pantheon compilation of SN Ia data and BAO data to constrain the model parameters using the χ2 minimization technique. We obtain the present values of Hubble constant H0 as 66.21.34+1.42, 70.70.31+0.32 and 67.741.04+1.24 for H(z), H(z) + Pantheon and H(z) + BAO respectively. In addition, we estimate the present age of the Universe in a derived model t0=14.380.64+0.63 for joint H(z) and pantheon compilation of SN Ia data which has only 0.88σ tension with its empirical value obtained in Plank collaboration. Moreover, the present values of the deceleration parameter q0 come out to be 0.550.038+0.031, 0.610.021+0.030 and 0.6270.025+0.022 by bounding the Universe in the derived model with H(z), H(z) + Pantheon compilation of SN Ia and H(z) + BAO data sets, respectively. We also have performed the state-finder diagnostics to discover the nature of dark energy. Full article
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14 pages, 4984 KiB  
Article
The Effects of Inertial Forces on the Dynamics of Disk Galaxies
by Roy Gomel and Tomer Zimmerman
Galaxies 2021, 9(2), 34; https://doi.org/10.3390/galaxies9020034 - 13 May 2021
Cited by 2 | Viewed by 3489
Abstract
When dealing with galactic dynamics, or more specifically, with galactic rotation curves, one basic assumption is always taken: the frame of reference relative to which the rotational velocities are given is assumed to be inertial. In other words, fictitious forces are assumed to [...] Read more.
When dealing with galactic dynamics, or more specifically, with galactic rotation curves, one basic assumption is always taken: the frame of reference relative to which the rotational velocities are given is assumed to be inertial. In other words, fictitious forces are assumed to vanish relative to the observational frame of a given galaxy. It might be interesting, however, to explore the outcomes of dropping that assumption; that is, to search for signatures of non-inertial behavior in the observed data. In this work, we show that the very discrepancy in galaxy rotation curves could be attributed to non-inertial effects. We derive a model for spiral galaxies that takes into account the possible influence of fictitious forces and find that the additional terms in the new model, due to fictitious forces, closely resemble dark halo profiles. Following this result, we apply the new model to a wide sample of galaxies, spanning a large range of luminosities and radii. It turns out that the new model accurately reproduces the structures of the rotation curves and provides very good fittings to the data. Full article
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20 pages, 850 KiB  
Article
Magnetized Particle Motion in γ-Spacetime in a Magnetic Field
by Ahmadjon Abdujabbarov, Javlon Rayimbaev, Farruh Atamurotov and Bobomurat Ahmedov
Galaxies 2020, 8(4), 76; https://doi.org/10.3390/galaxies8040076 - 29 Oct 2020
Cited by 20 | Viewed by 2375
Abstract
In the present work we explored the dynamics of magnetized particles around the compact object in γ-spacetime in the presence of an external asymptotically-uniform magnetic field. The analysis of the circular orbits of magnetized particles around the compact object in the spacetime [...] Read more.
In the present work we explored the dynamics of magnetized particles around the compact object in γ-spacetime in the presence of an external asymptotically-uniform magnetic field. The analysis of the circular orbits of magnetized particles around the compact object in the spacetime of a γ-object immersed in the external magnetic field has shown that the area of stable circular orbits of magnetized particles increases with the increase of γ-parameter. We have also investigated the acceleration of the magnetized particles near the γ-object and shown that the center-of-mass energy of colliding magnetized particles increases with the increase of γ-parameter. Finally, we have applied the obtained results to the astrophysical scenario and shown that the values of γ-parameter in the range of γ(0.5,1) can mimic the spin of Kerr black hole up to a0.85, while the magnetic interaction can mimic the γ-parameter at γ(0.8,1) and spin of a Kerr black hole up to a0.3. Full article
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