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Volume 102 • Number 2 • February 2024

Articles

Vol. 102No. 2pp. 69–84
Many models have been proposed to minimize the dark matter (DM) content in various astronomical objects at every scale in the Universe. The most widely known model is MOdified Newtonian dynamics (MOND). MOND was first published by Mordehai Milgrom in 1983. A second concurrent model is modified gravity, which is a covariant scalar–tensor–vector extension of general relativity. Other theories also exist but have not been broadly applied to a large list of astronomical objects. Eventually, we can also mention the Newtonian fractional-dimension gravity, a gravity theory based on spaces with fractional (i.e., non-integer) dimension. A new model, called κ-model, based on very elementary phenomenological considerations, has recently been proposed in the astrophysics field. This model shows that the presence of DM can be considerably minimized with regard to the dynamics of galaxies. The κ-model belongs to the general family of theories descended from MOND. Under this family of theories, there is no need to develop a highly uncertain DM sector of physics to explain the observations.
Vol. 102No. 2pp. 85–95
Aim of this paper is to investigate an anisotropic locally rotationally symmetric (LRS) Bianchi type-I space–time in the context of the recently proposed f(Q, T) gravity, where Q is the non-metricity scalar and T is energy–momentum tensor. We have considered f(Q, T) = αQ + βT a linear form, where α and β are model parameters. We have analyzed the exact solution of LRS Bianchi type-I space–time by assuming relation between metric potential A = B n , where n is arbitrary non-zero real number. To study the anisotropic nature of the dynamical dark energy, we assume that the skewness parameters are time dependent and n ≠ 1. We have constrained to our model by using observational Hubble dataset. Onwards, discussed the physical behavior of cosmological parameters such as energy density, pressure, EoS parameter, deceleration parameter and, Energy conditions.
OPEN ACCESS
Vol. 102No. 2pp. 96–99
We calculate the Big Bang nucleosynthesis abundances for helium-4 and deuterium for a range of neutron lifetimes, τn = 840–1050 s, using the state-of-the-art Python package PRyMordial. We show the results for two different nuclear reaction rates, calculated by NACRE II and the PRIMAT collaborations.
Vol. 102No. 2pp. 100–112
We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric (M.C. Durgapal, J. Phys. A: Math. Gen. 15, 2637 (1982)). In this work, we investigate the effects of the scale parameter k on the local matter distribution. Here, we have chosen the compact star candidate SMC X-1 with observed values of mass = (1.29 ± 0.05) M and radius
cover
km, respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here, we solve the modified Einstein field equations in the presence of the background metric γμν. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For rk, the background de Sitter space–time reduces into Minkowski form, and the coupling vanishes. We discuss certain physical quantities of our obtained solution, such as density, isotropic pressure, sound speed, pressure-density gradients, compactness, and surface redshift, to claim the physical viability of our model. It is found that our model clearly satisfies all the energy conditions, the causality condition, and the dynamical equilibrium via a modified Tolman–Oppenheimer–Volkov equation. Finally, we can conclude that our proposed model is physically realistic and well behaved.
Vol. 102No. 2pp. 113–118
This work reported the investigation of optical spectra of Rh-like Xe9+ and Ru-like Xe10+ ions at a low-energy electron beam ion trap. The line from 4d9 2D3/22D5/2 M1 transition of Xe9+ ions was remeasured, the wavelength of which was determined to be 598.365(5) nm, and the uncertainty was significantly improved. In the region of 200–700 nm, four spectral lines emitted from Xe10+ ions were directly observed for the first time. The relativistic many-body perturbation method was adopted for the investigation of fine structure in Xe10+ ions. The theoretical and experimental results were in good agreement within 2%, and the four observed lines of Xe10+ ions were identified.
Vol. 102No. 2pp. 119–126
In the present study, we have described the accelerated cosmological models of the universe in f(Q) gravity. In f(Q) gravity, the gravitational field equations are modified by a function of the non-metricity tensor, which characterizes the deviation of the affine connection from the metric compatibility condition. We have considered two different forms of f(Q) gravity as f(Q) = β + αQ(n + 1) and f(Q) = βQ + αQ n to explain the dynamics of the expanding universe. We have discussed the dynamics of the universe through graphical representation by considering the power law ( a = kt m ). The free parameters of the models are fitted with the latest observational data set of observational Hubble data, consisting of 57 points, using statistical analysis based on the Markov Chain Monte Carlo method. The best-fit values for the model’s parameter are estimated as H0 = 67.3 ± 1.1, m = 1.0213 ± 0.0071, and k = 65.4 ± 1.1. The parameters of the derived model, like energy density, isotropic pressure, EoS (Equation of state) parameter, and jerk parameter, are discussed. We have described the energy conditions to explain the viability of the considered models. We have also verified the stability of the derived model through perturbation analysis.

Tutorial

Vol. 102No. 2pp. 127–137
We present a simple model of a metal in a gravitational field in order to show some physical features that help in understanding how the metal holds itself up against gravity. The nuclei are held up against gravity by their bound electron(s) as well as the electric field due to all the gravitationally induced electric dipoles at other lattice sites; these dipoles result from the bound electrons sinking, in response to the gravitational field, by a smaller distance than the nuclei. We also consider the conduction electrons to be held up by Fermi pressure. We use the model to estimate the magnitude of the gravitationally induced electric field in a metal and to establish its direction. We work in the low temperature limit.

Retractions

List of Issues
Volume 102
Issue 2
February 2024
Volume 102
Issue 1
January 2024
Volume 101
Issue 12
December 2023
Volume 101
Issue 11
November 2023
Volume 101
Issue 10
October 2023
Volume 101
Issue 9
September 2023