arXiv subjects

Hooman Moradpour

Publications and source records attributed to Hooman Moradpour.

17 recordsLinked to original sources

arXiv2026

Constraints on Rastall gravity from current observational data

We study the cosmological features of Rastall gravity, where the covariant energy-momentum conservation is modified to $\nabla_{\mu}T^{\mu}_{\nu}=\lambda \nabla_{\nu}R$ in curved spacetime. For this purpose, we obtain the modified field equations of Rastall model to linear order of perturbations, and then inspect the evolutionary behavior of cosmological observables, chiefly the matter power spectrum and the Hubble parameter, within the context of Rastall gravity. We also compare Rastall model with cosmological probes, namely cosmic microwave background, weak lensing, supernovae, baryon acoustic oscillations, and redshift-space distortions data. According to our numerical results, Rastall gravity prefers lower growth of structures compared to the $\Lambda$CDM model, which indicates consistency with low-redshift large-scale structure probes. Moreover, numerical analysis reveals that Rastall gravity with a cosmological constant as the dark energy component suffers from the Hubble tension, like the $\Lambda$CDM model.

physics.gen-ph↗

arXiv2026

Observational Constraints on Emergent Fractional Fractal Cosmology

We constrain the Emergent Fractional Fractal (EFF) cosmological model through a joint likelihood analysis of recent cosmological observations at the background and perturbation levels. In this framework, an effective fractal dimension $d$ is introduced to parameterize possible fractional deviations from the standard cosmological model. We consider three combinations of datasets: (i) late-time (LT) observations including PantheonPlus Type Ia supernovae, $H(z)$ measurements, and growth-rate measurements $f\sigma_8$; (ii) LT combined with DESI DR2 BAO and Big Bang nucleosynthesis (BBN); and (iii) LT combined with DESI DR2 BAO and CMB distance priors. With the inclusion of CMB distance priors, the fractal dimension is constrained to $d = 2.0004^{+0.0006}_{-0.0003}$ at the $1\sigma$ confidence level. Model comparison using the Akaike Information Criterion (AIC) shows that the EFF and $\Lambda$CDM models fit the observational data equally well, while the Bayesian Information Criterion (BIC) favors the simpler $\Lambda$CDM model because of its smaller parameter space. These results show that current cosmological observations place strong constraints on fractal extensions of the standard cosmological framework and possible deviations from the $\Lambda$CDM model.

gr-qc↗

arXiv2025

A Double-Sine-Gordon Early Universe

A solitonic model of the early universe is introduced by employing the Double-Sine-Gordon (DSG) potential. The model predicts the appropriate number of e-foldings ($N_e$) required for favored inflation and is an advantage for the model in addressing the flatness, horizon, and magnetic monopole problems. Compatibility of the model with observations, including the Planck $2018$ data \cite{Akrami et al. (2020)} and the Planck $2018$ data+BK$18$+BAO \cite{Ade et al. (2021)} paves the way to estimate the model's free parameters. The results generate acceptable and proper values for the spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) in agreement with the Planck $2018$ data \cite{Akrami et al. (2020)} and the Planck $2018$ data+BK$18$+BAO \cite{Ade et al. (2021)}. Correspondingly, a consistent description of the reheating era is obtained, yielding positive reheating number of e-foldings ($N_{\mathrm{reh}}$) and reheating final temperature ($T_{\mathrm{reh}}$) from $10^{-2}$ GeV to $10^{16}$ GeV. Overall, the model seems viable at the inflationary and reheating eras.

astro-ph.CO↗

arXiv2024

The shadows of quantum gravity on Bell's inequality

This study delves into the validity of quantum mechanical operators in the context of quantum gravity, recognizing the potential need for their generalization. A primary objective is to investigate the repercussions of these generalizations on the inherent non-locality within quantum mechanics, as exemplified by Bell's inequality. Additionally, the study scrutinizes the consequences of introducing a non-zero minimal length into the established framework of Bell's inequality. The findings contribute significantly to our theoretical comprehension of the intricate interplay between quantum mechanics and gravity. Moreover, this research explores the impact of quantum gravity on Bell's inequality and its practical applications within quantum technologies, notably in the realms of device-independent protocols, quantum key distribution, and quantum randomness generation.

quant-ph↗

arXiv2024

Effective information bounds in modified quantum mechanics

A common feature of collapse models and an expected signature of the quantization of gravity at energies well below the Planck scale is the deviation from ordinary quantum-mechanical behavior. Here, we analyze the general consequences of such modifications from the point of view of quantum information theory and we anticipate applications to different quantum systems. We show that quantum systems undergo corrections to the quantum speed limit which, in turn, imply the modification of the Heisenberg limit for parameter estimation. Our results hold for a wide class of scenarios beyond ordinary quantum mechanics. For some nonlocal models inspired by quantum gravity, the bounds are found to oscillate in time, an effect that could be tested in future high-precision quantum experiments.

quant-ph↗

arXiv2022

Einstein Static Universe and its Stability in Generalized Rastall Gravity

The Einstein static (ES) state is a good candidate for describing the very early universe in terms of a regular cosmological model in which the Big Bang singularity is avoided. In the present study we propose an ES solution in the framework of generalized Rastall gravity (GRG), a modified version of original Rastall theory in which the coupling parameter is allowed to vary with respect to the spacetime coordinates. Introducing an ansatz for the Rastall parameter, existence and the corresponding stability of the solutions are investigated. We show that the GRG is capable of describing a stable singularity-free state for the universe. The problem of transition from an ES to an inflationary state is also addressed. We find that a time variation of the equation of state parameter from values lying in the range |w|<1/3 to the value w=-1/3 can give rise to such a phase transition. The vector and tensor perturbations around the ES solution are studied, as well. In the case of GRG, the vector perturbations remain frozen, nevertheless, the tenor perturbations can grow in such a way that the ES solution remains stable provided the ratio of Rastall gravitational constant to the Einsteinian one always exceeds a minimum value for each tensor mode.

gr-qc↗

arXiv2022

A dynamical system representation of generalized Rastall gravity

In this work we study the phase-space analysis of generalized Rastall gravity (GRG) which has recently been introduced as a modification to the original version of Rastall gravity (RG). In GRG, the coupling parameter assumes a dynamical feature and may play the role of dark energy (DE) which is responsible for the present accelerating expansion of the Universe. Our investigation shows that such a modification of General Relativity (GR) admits a stable critical point corresponding to the late time accelerated expansion of the Universe. Assuming both dark matter (DM) and an ultra-relativistic perfect fluid (radiation) as the cosmic ingredients, we find that the underlying model presents a viable sequence of cosmic evolution, beginning from radiation dominated era passing then through DM domination and finally reaches the late time DE dominated era. Moreover, taking into account the contribution due to the spatial curvature within the total energy density leads to a growing mode for it in such a way that its present values are consistent with those reported in recent observations. We also present a numerical simulation of the model which particularizes our dynamical system representation. These studies demonstrate the ability of GRG to describe the present accelerated expansion of the Universe.

gr-qc↗

arXiv2022

Gamow Temperature in Tsallis and Kaniadakis Statistics

Relying on the quantum tunnelling concept and Maxwell-Boltzmann-Gibbs statistics, Gamow shows that the star-burning process happens at temperatures comparable to a critical value, called the Gamow temperature ({\tt T}) and less than the prediction of the classical framework. In order to highlight the role of the equipartition theorem in the Gamow argument, a thermal length scale is defined, and then the effects of non-extensivity on the Gamow temperature have been investigated by focusing on the Tsallis and Kaniadakis statistics. The results attest that while the Gamow temperature decreases in the framework of Kaniadakis statistics, it can be bigger or smaller than {\tt T} when Tsallis statistics are employed.

cond-mat.stat-mech↗

arXiv2021

Constraining the generalized uncertainty principle with neutron interferometry

The non-zero minimal length arises in various theories of gravity, leading to the so-called generalized uncertainty principle (GUP). In this short paper we analyze the GUP effects on neutron interferometry, showing that the obtained phase shifts depend on the mass and velocity of the particle. New upper bounds on the dimensionless GUP parameter have been found that are in agreement with the literature.

gr-qc↗

arXiv2021

Non-minimal coupling inspires the Dirac cosmological model

In the framework of the generalized Rastall theory (GRT), we study the ability of a non-minimal coupling between geometry and matter fields in order to provide a setting which allows for a variable G during the cosmic evolution. In this regard, the compatibility of this theory with Dirac hypothesis on the variations of G is investigated, and additionally, the possibility of obtaining the current accelerated universe is also addressed. In summary, our study indicates that, in GRT, having in hand the G profile, one may find the corresponding non-minimal coupling between the energy source and geometry and vise versa, in a compatible way with the current accelerated universe.

gr-qc↗

arXiv2021

A Note on Effects of Generalized and Extended Uncertainty Principles on Jüttner Gas

In recent years, the implications of the generalized (GUP) and extended (EUP) uncertainty prin-ciples on Maxwell-Boltzmann distribution have been widely investigated. However, at high energy regimes, the validity of Maxwell-Boltzmann statistics is under debate and instead, the Jüttner distribution is proposed as the distribution function in relativistic limit. Motivated by these considerations, in the present work, our aim is to study the effects of GUP and EUP on a system that obeys the Jüttner distribution. To achieve this goal, we address a method to get the distribution function by starting from the partition function and its relation with thermal energy which finally helps us in finding the corresponding energy density states.

gr-qc↗

arXiv2021

Evolving traversable wormholes satisfying the energy conditions in the presence of pole dark energy

We consider the evolution of traversable wormhole geometries in the inflationary, radiation -- and matter -- dominated eras, and dynamic wormholes with a traceless energy-momentum tensor (EMT), within the recently proposed {\it pole dark energy} model. We show that the evolving radiation -- and matter -- dominated wormhole spacetimes satisfy the null energy condition (NEC), but possess negative energy densities at late times, thus violating the weak energy condition (WEC) in this specific domain. However, we demonstrate with a specific example that the traceless EMT evolving wormholes, supported by conformally invariant massless fields, in principle, could satisfy the WEC, and consequently the NEC, at all times and for all values of the radial coordinate. Thus, one may imagine a scenario in which these geometries originate in the Planckian era through quantum gravitational processes. Inflation could then provide a natural mechanism for the enlargement of these Planckian wormholes, where their FLRW background evolution is governed by pole dark energy. For the first time in the literature, specific dynamical $4$-dimensional solutions are presented that satisfy the NEC and WEC everywhere and everywhen.

gr-qc↗

arXiv2019

On the general relativistic framework of the Sagnac effect

The Sagnac effect is usually considered as being a relativistic effect produced in an interferometer when the device is rotating. General relativistic explanations are known and already widely explained in many papers. Such general relativistic approaches are founded on Einstein's equivalence principle (EEP), which states the equivalence between the gravitational "force" and the pseudo-force experienced by an observer in a non-inertial frame of reference, included a rotating observer. Typically, the authors consider the so-called Langevin-Landau-Lifschitz metric and the path of light is determined by null geodesics. This approach partially hides the physical meaning of the effect. It seems indeed that the light speed varies by c\pmωr in one or the other direction around the disk. In this paper, a slightly different general relativistic approach will be used. The different "gravitational field" acting on the beam splitter and on the two rays of light is analyzed. This different approach permits a better understanding of the physical meaning of the Sagnac effect.

gr-qc↗

arXiv2018

Thermodynamics in Rastall Gravity with Entropy Corrections

We explore the thermodynamic analysis at the apparent horizon in the framework of Rastall theory of gravity. We take different entropies such as the Bakenstein, logarithmic corrected, power law corrected, and the Renyi entropies. We investigate the first law and generalized second law of thermodynamics analytically for these entropies which hold under certain conditions. Furthermore, the behavior of the total entropy in each case is analyzed. As a result, it is implied that the generalized second law of thermodynamics is satisfied. We also check whether the thermodynamic equilibrium condition for these entropies is met at the present horizon.

physics.gen-ph↗

arXiv2016

Entropic gravity from noncommutative black holes

In this paper we will investigate the effects of a noncommutative (NC) space-time on the dynamics of the universe. We will generalize the black hole entropy formula for a NC black hole. Then, using the entropic gravity formalism, we will show that the noncommutativity changes the strength of the gravitational field. By applying this result to a homogeneous and isotropic universe containing nonrelativistic matter and a cosmological constant, we will show that the model modified by the noncommutativity of the space-time is a better fit to the obtained data than the standard one.

gr-qc↗

arXiv2016

Thermodynamic analysis of the static spherically symmetric field equations in Rastall theory

The restrictions on the Rastall theory due to apply the Newtonian limit to the theory are derived. In addition, we use the zero-zero component of the Rastall field equations as well as the unified first law of thermodynamics to find the Misner-Sharp mass content confined to the event horizon of the spherically symmetric static spacetimes in the Rastall framework. The obtained relation is calculated for the Schwarzschild and de-Sitter back holes as two examples. Bearing the obtained relation for the Misner-Sharp mass in mind together with recasting the one-one component of the Rastall field equations into the form of the first law of thermodynamics, we obtain expressions for the horizon entropy and the work term. Finally, we also compare the thermodynamic quantities of system, including energy, entropy and work, with their counterparts in the Einstein framework to have a better view about the role of the Rastall hypothesis on the thermodynamics of system.

gr-qc↗

arXiv2015

Dynamic conformal spherically symmetric solutions in an accelerated background

We consider dynamical spherically symmetric spacetimes, which are conformal to the static spherically symmetric metrics, and find new solutions of Einstein equations by symmetry considerations. Our study help us classify various conformal Black Holes that are embedded within a dynamic background into the one class of solutions with the same conformal symmetry. In addition, Thermodynamics, mathematical and gravitational properties are addressed. These solutions point to have a better resolution of the meaning of the Black Holes in the dynamic background.

gr-qc↗