arXiv subjects

H. Moradpour

Publications and source records attributed to H. Moradpour.

At least 19 recordsLinked to original sources

arXiv2026

Finite Hilbert space and maximum mass of Schwarzschild black holes from a Generalized Uncertainty Principle

We show that implementing a generalized uncertainty principle (GUP) with both minimal length and maximal momentum directly on the reduced phase space of the Schwarzschild black hole (BH) leads to a finite and discrete mass spectrum, a strict upper bound on the BH mass, a bounded entropy, and a fully regulated Hawking temperature. We further construct a GUP-deformed lapse function that preserves the ADM mass and horizon radius while exactly reproducing the GUP temperature through the surface gravity. Using the most massive observed supermassive BHs, we derive the constraint on the GUP parameter, $\beta\lesssim 10^{-98}$, showing that present astrophysical data already impose robust bounds on minimal length quantum gravity.

gr-qc↗

arXiv2026

$q$-Deformed Quantum Mechanics and the Thermodynamics of Black Hole/White Hole Spectral pair

In this work, we investigate the thermodynamics of Schwarzschild black and white holes within a $q$-deformed Wheeler--DeWitt framework. By introducing a $q$-deformed Heisenberg--Weyl algebra at a root of unity, we derive a finite-dimensional Hilbert space, a bounded mass spectrum, and an adiabatic invariant leading to a bounded entropy-mass relation. The deformation results in a universal logarithmic correction, as well as a minimum temperature and a maximum entropy that matches the de Sitter bound. Also, we examine the interpretation of a cold remnant, which is dynamically stable because its radiation rate approaches zero, even though its heat capacity remains negative. We also explore the holographic implications of this limited entropy. Our results thus provide a consistent semiclassical picture, where quantum deformation naturally introduces an entropy bound, avoids divergences at the final evaporation stage, and suggests a smooth transition from quantum gravity to cosmology.

gr-qc↗

arXiv2026

Constraining fractionality using some observational tests

Recently, a fractional version of the Schwarzschild-Tangherlini black hole with a fractal horizon has been introduced. Motivated by the key role of the Schwarzschild solution in gravitational and astrophysical studies, some consequences of this fractional-fractal generalization of the Schwarzschild black hole have been investigated. In this line, the corresponding i) Shapiro and Sagnac time delays, ii) shadow, iii) orbital precession, and iv) gravitational lensing are studied and confronted with observational data. MCMC analysis also unveils i) the potential of this metric in dealing with the solar-system tests and ii) the necessity of studying fractional spacetimes and objects.

gr-qc↗

arXiv2026

Quantum corrected thermodynamics and horizon quantization of the Reissner--Nordstr\"om black hole

In this letter, we develop a unified semiclassical framework for the thermodynamics and quantization of the Reissner--Nordstr\"om (RN) black hole (BH) based on the Misner--Sharp--Hernandez (MSH) mass. Treating the quasi-local horizon energies as the relevant thermodynamic variables, we formulate a horizon-by-horizon first law and Smarr relation. Using a reduced phase-space quantization, we obtain a discrete MSH mass spectrum for both horizons, which reproduces the minimal entropy spacing. Quantum transitions between adjacent levels yield Planck-scale corrections to the Hawking temperatures and a universal logarithmic contribution to the entropy, consistent with independent approaches to quantum gravity. We encode these corrections into a quantum-deformed RN geometry via a simple multiplicative factor that preserves the classical horizon positions while reproducing the corrected surface gravities. The associated effective stress tensor behaves as a conserved vacuum-polarization source with characteristic $r^{-4}$ falloff and a small trace, providing a compact representation of semiclassical backreaction. The deformation slightly lowers both horizon temperatures, weakens the inner-horizon instability, and induces tiny shifts in photon-sphere and shadow observables for macroscopic BHs.

gr-qc↗

arXiv2026

Reduced Phase Space Quantization and Quantum Corrected Entropy of Schwarzschild-de Sitter Horizons

This paper investigates the quantization of the Schwarzschild--de Sitter (SdS) black hole (BH) using the Misner--Sharp--Hernandez (MSH) mass as the internal energy in a reduced phase space framework. After introducing the canonical variables of the reduced phase space, we derive a discrete spectrum for the surface areas of the BH event horizon (EH) as well as MSH masses. We utilized the MSH mass spectrum to obtain the entropy of the BH. The entropy of the BH and cosmic EHs reveals a logarithmic correction to the Bekenstein--Hawking term. Our results support the robustness of the logarithmic form of quantum corrections in SdS thermodynamics.

gr-qc↗

arXiv2026

Minimal length: A source of quantum non-locality

The narrow and subtle difference between the Hilbert spaces of operators corresponding to the canonical momentum and the generalized momentum that includes minimal length effects is polished. Consequently, complex eigenvalues may be allowed for the canonical momentum operator due to the existence of minimal length. A novel quantum entanglement generation is also reported indicating the power of theories including a minimal length in enriching the current understanding of quantum non-locality.

quant-ph↗

arXiv2025

Fractional Schwarzschild-Tangherlini black hole with a fractal event horizon

We demonstrate that the implementation of the fractional and non-local Wheeler--DeWitt (WDW) equation within the context of Schwarzschild geometry leads to the emergence of a Schwarzschild--Tangherlini black hole (BH), which is uniquely characterized by an event horizon that exhibits fractal properties and is defined by a non-integer dimension that lies in the continuum between the values of 1 and 2. Our calculations further reveal that this intriguing fractional BH may potentially possess a temperature that is substantially lower than that of a conventional BH, thereby suggesting a significant deviation from the expected thermodynamic properties of standard BHs. These remarkable characteristics, which are intrinsically linked to the non-integer dimensionality of the event horizon, likely arise from applying the Riesz fractional derivative as a sophisticated non-local operator, thus introducing fascinating dynamics into the theoretical framework of BH physics.

gr-qc↗

arXiv2025

Fractional entropy of the Brown-Kucha\v{r} dust in fractional anti-de Sitter quantum gravity

This study derives the mass spectrum and entropy of the Brown-Kucha\v{r} dust in anti-de Sitter (AdS) spacetime using the fractional Wheeler-DeWitt (WDW) equation. The generalized fractional WDW equation is formulated using a fractional quantization map, demonstrating a correlation between the fractal mass dimension of the Brown-Kucha\v{r} dust and L\'evy's fractional parameter $\alpha$ of the Riesz fractional quantum operator. These findings may provide new insights into the ramifications of the fractal behavior of cosmic structures in quantum cosmology and quantum gravity.

gr-qc↗

arXiv2024

Fractional Stars

This study examines the possibility of starting the process of collapsing and forming stars from a fractional molecular cloud. Although the Verlinde's approach is employed to derive the corresponding gravitational potential, the results are easily generalizable to other gravitational potential proposals for fractional systems. It is due to the fact that the different methods, despite the difference in the details of results, all obtain power forms for the potential in terms of radius. An essential result of this analysis is the derivation of the corresponding Jeans mass limit, which is a crucial parameter in understanding the formation of stars. The study shows that the Jeans mass of a cloud in fractional gravity is much smaller than the traditional value. In addition, the study also determines the burning temperature of the resulting star using the Gamow theory. This calculation provides insight into the complex processes that govern the evolution of these celestial bodies. Finally, the study briefly discusses the investigation of hydrostatic equilibrium, a crucial condition that ensures the stability of these fractional stars. It also addresses the corresponding Lane--Emden equation, which is pivotal in understanding this equilibrium.

gr-qc↗

arXiv2024

Holographic vacuum energy regularization and corrected entropy of de Sitter space

We propose that the spectrum of the surface area of the apparent horizon (AH) of de Sitter (dS) spacetime leads to corrected temperature and entropy of the dS spacetime, offering new insights into its thermodynamic properties. This is done by employing the spectrum of the AH radius, acquired from the Wheeler--DeWitt (WDW) equation, together with the Stefan--Boltzmann law, the time-energy uncertainty relation, and the unified first law of thermodynamics.

gr-qc↗

arXiv2024

Friedmann equations of the fractal apparent horizon

From a fractal perspective, the entropy bound of gravitational systems undergoes changes. Furthermore, in the cosmological setting, the conservation law of a perfect fluid is also altered in such systems, affecting spatial elements like volume, area, and radius. By applying the first law of thermodynamics and deriving the Friedmann equations, we can gain insight into the evolution of such a fractal cosmos. However, observations continue to necessitate the existence of a dark energy source. To address this, in this article, we have created a novel fractal $\Lambda$CDM cosmological model and determined the fractal cosmological observables. We show that the spatial fractal dimension is two, and the age of the Universe is 13.91 Gyr, by fitting the model's parameters to cosmological data.

gr-qc↗

arXiv2024

Gravitational Collapse without Singularity Formation in Brans-Dicke Theory

In the present work we study collapse process of a homogeneous and isotropic fluid in Brans-Dicke ({BD}) theory with non-vanishing spacetime torsion. In this theory, torsion can be generated by the {BD} scalar field as well as the intrinsic angular momentum (spin) of matter. Assuming the matter content of the collapsing body to be a Weyssenhoff fluid, which is a generalization of perfect fluid in general relativity ({GR}) in order to include the spin effects, we find that in BD theory with torsion, the existence of spin effects could avoid the spacetime singularity that forms in the original version of this theory (Scheel et al. in Phys Rev D 51:4208, 1995, Scheel et al. in Phys Rev D 51:4236, 1995). Numerical simulations of collapse model show that the spacetime singularity is replaced by a non-singular bounce, the spacetime event at which the collapse process halts at a minimum radius and then turns into an expanding phase. Moreover, the model parameters can be set so that the apparent horizon will never meet the boundary of the collapsing body so that the bounce event can be detectable by external observers in the Universe.

gr-qc↗

arXiv2023

Modified cosmology from quantum deformed entropy

In Ref. [S. Jalalzadeh, Phys. Lett. B 829 (2022) 137058], Jalalzadeh established that the thermodynamical entropy of a quantum-deformed black hole with horizon area $A$ can be written as $S_q=π\sin\left(\frac{A}{8G\mathcal N} \right)/\sin\left(\fracπ{2\mathcal N} \right)$, where $\mathcal N=L_q^2/L_\text{P}^2$, $L_\text{P}$ being the Planck length and $L_q$ denoting, generically, the q-deformed cosmic event horizon distance $L_q$. Motivated by this, we now extend the framework constructed in [S. Jalalzadeh, Phys. Lett. B 829 (2022) 137058] towards the Friedmann and Raychaudhuri equations describing spatially homogeneous and isotropic universe dynamics. Our procedure in this paper involves a twofold assumption. On the one hand, we take the entropy associated with the apparent horizon of the Robertson-Walker universe in the form of the aforementioned expression. On the other hand, we assume that the unified first law of thermodynamics, $dE=TdS+WdV$, holds on the apparent horizon. Subsequently, we find a novel modified cosmological scenario characterized by quantum-deformed (q-deformed) Friedmann and Raychaudhuri equations containing additional components that generate an effective dark energy sector. Our results indicate an effective dark energy component, which can explain the Universe's late-time acceleration. Moreover, the Universe follows the standard thermal history, with a transition redshift from deceleration to acceleration at $z_\text{tran}=0.5$. More precisely, according to our model, at a redshift of $z = 0.377$, the effective dark energy dominates with a de Sitter universe in the long run. We include the evolution of luminosity distance, $μ$, the Hubble parameter, $H(z)$, and the deceleration parameter, $q(z)$, versus redshift. Finally, we have conducted a comparative analysis of our proposed model with others involving non-extensive entropies.

gr-qc↗

arXiv2023

Some applications of the Shapiro time delay

Listening to echoes has long been a way to estimate distances, a technique whose backbone is the time delay. The gravitational field also creates a time delay, called Shapiro time delay, that helps us extract some information from the field and is indeed due to the photon journey through the field. Here, the ability of the Shapiro effect to distinguish naked singularities from non-naked ones (black holes) is discussed. It is also inferred that this time delay may be hired to compare the various types of singularities with different dimensions. Besides them, the possibility of detecting the rotation of the assumed objects through surveying the gravitational time delay is also addressed.

gr-qc↗

arXiv2023

On the thermodynamics of reconciling quantum and gravity

Is thermodynamics consistent with the quantum gravity reconciliation hypothesis [A. G. Cohen et al. Phys. Rev. Lett. 82, 4971 (1999)], which establishes holographic dark energy models? Here, we have attempted to address this issue in the affirmative by concentrating on the first law of thermodynamics.

gr-qc↗

arXiv2022

The third law of thermodynamics, non-extensivity, and energy definition in black hole physics

Working in the framework of generalized statistics, the problem of establishing the third law of thermodynamics in the black hole physics is studied by focusing on Schwarzschild black hole which easily and clearly exposes the violation of this law in the common approach based on Bekenstein entropy. Additionally, it is addressed that some inconsistencies between the predictions of quantum field theory and thermodynamics about the black hole temperature may be reconciled by using the thermodynamics laws in order to broaden energy definition. It claims that thermodynamics should be employed as a powerful tool in looking for more comprehensive energy definitions in high-energy physics, still mysterious.

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↗

arXiv2022

On Some Applications of the Sagnac Effect

Considering exact spacetimes representing rotating black holes and naked singularities, we study the possibility that the Sagnac effect detects $i$) higher dimensions, $ii$) rotation of black holes in higher dimension, and also, $iii$) distinguishes black holes from naked singularities. The results indicate that the Sagnac time delay gets affected by the presence of extra-dimension or its associated angular momentum. This time delay is also different in the spacetime of a naked singularity compared to that of a black hole. Hence, the Sagnac effect may be used as an experiment for better understanding of spacetimes with higher dimensions or those that admit naked singularities.

gr-qc↗