arXiv subjects

N. Sadeghnezhad

Publications and source records attributed to N. Sadeghnezhad.

8 recordsLinked to original sources

arXiv2025

Observational constraints on New Tsallis holographic energy in Rastall theory

The cosmological implications of New Tsallis holographic dark energy (NTHDE) in Rastall theory have been studied. Using the data set that includes DESI BAO (DR2), PantheonPlus SNe Ia, H(z) measurements, and BBN and the MCMC analysis, the key cosmological and model-specific parameters are constrained. The result is compared with that of the ΛCDM model indicating that in addition to providing a viable dynamical dark energy framework, predictions for H(z) are slightly more consistent with intermediate-redshift observations. Generally, the model remains compatible with current data and offers testable deviations from ΛCDM for upcoming surveys. It is also seen that when the energy density of quantum fields in vacuum, exposed by NTHDE, is combined with the Rastall correction term to the general relativity, a plausible candidate for dynamical dark energy is obtained that mimic the current value of the dark energy density parameter reported in the ΛCDM model. The latter cannot be repeated by NTHDE alone. The study also confirms previous theoretical and observational constraints on the Rastall parameter obtained by focusing on the thermodynamics, early universe, pulsars, and the early-type galaxies.

astro-ph.CO↗

arXiv2022

Entropic Gravity and Cosmology in Kaniadakis Statistics

By using the Kaniadakis statistics, we discuss the modifications of Newtonian gravity and radial velocity profile in the light of Verlinde's formalism for gravitational entropy. After considering the implications of k-statistics on the gravitational potential, it is shown that an accelerated universe may be obtained by considering the Friedmann first equation in this non-extensive statistics.

gr-qc↗

arXiv2022

Generalized uncertainty principle and burning stars

Gamow's theory of the implications of quantum tunneling on the star burning has two cornerstones including quantum mechanics and equipartition theorem. It has vastly been proposed that both of these foundations are affected by the existence of a non-zero minimum for length which usually appears in quantum gravity scenarios and leads to the Generalized Uncertainty principle (GUP). Mathematically, in the framework of quantum mechanics, the effects of GUP are considered as perturbation terms. Here, generalizing the de Broglie wavelength relation in the presence of minimal length, GUP correction to the Gamow's temperature is calculated and in parallel, an upper bound for the GUP parameter is estimated.

gr-qc↗

arXiv2019

A note on cosmological features of modified Newtonian potentials

Considering some modified Newtonian potentials and the Hubble law in writing the total energy of a test mass located at the edge of a flat Friedmann-Robertson-Walker universe, we obtain several modified Friedmann equations. Interestingly enough, our study shows that the employed potentials, while some of them have some successes in modelling the spiral galaxies rotation curves, may also address an accelerated universe. This fact indicates that dark energy and dark matter may have some common origins and aspects.

physics.gen-ph↗

arXiv2017

Thermodynamic analysis of gravitational field equations in Lyra manifold

Considering the Einstein field equations in Lyra manifold, and applying the unified first law of thermodynamics as well as the Clausius relation to the apparent horizon of FRW universe, we find the entropy of apparent horizon in Lyra manifold. In addition, the validity of second law of thermodynamics and its generalized form are also studied. Finally, we use the first law of thermodynamics in order to find the horizon entropy of static spherically symmetric spacetimes. Some results of considering (anti)de-Sitter and Schwarzschild metrics have also been addressed.

gr-qc↗

arXiv2017

Traversable asymptotically flat wormholes in Rastall gravity

There are some gravitational theories in which the ordinary energy-momentum conservation law is not valid in the curved spacetime. Rastall gravity is one of the known theories in this regard which includes a non-minimal coupling between geometry and matter fields. Equipped with the basis of such theory, we study the properties of traversable wormholes with flat asymptotes. We investigate the possibility of exact solutions by a source with the baryonic matter state parameter. Our survey indicates that Rastall theory has considerable effects on the wormhole characteristics. In addition, we study various case studies and show that the weak energy condition may be met for some solutions. We also give a discussion regarding to traversability of such wormhole geometry with phantom sources.

gr-qc↗

arXiv2016

A Note on Coherent States with Quantum Gravity Effects

Existence of a minimal measurable length and an upper bound for the momentum fluctuations are the casting reasons for generalization of uncertainty principle and then reformulation of Hilbert space representation of quantum mechanics. In this paper, we study the consequences of the Generalized Uncertainty Principle (GUP) in the presence of both minimal length and maximal momentum. We consider a simple harmonic oscillator in the framework of GUP by introducing it's energy eigenstates and energy spectrum. Investigation of coherent states for a generalized harmonic oscillator and it's generic behavior are the other topics in our study.

gr-qc↗

arXiv2014

Gravitational Radiation in Noncommutative Gravity

The gravitational radiation power of a binary system in a noncommutative space is derived and it's rate of the period decrease is calculated to first order in noncommutativity parameter. By comparing the theoretical results with the observational data of the binary pulsar PSR 1913+16, we find a bound on the noncommutativity parameter.

gr-qc↗