arXiv subjects

Homa Shababi

Publications and source records attributed to Homa Shababi.

10 recordsLinked to original sources

arXiv2025

The solution space of a five-dimensional geometry: Kundt spacetimes and cosmological time-crystals

We uncover the solution space of a five dimensional geometry which we deem it as the direct counterpart of the Bianchi Type V cosmological model. We kinematically reduce the scale factor matrix and then, with an appropriate scaling and choice of time, we cast the spatial equations into a simple "Kasner" like form; thus revealing linear integrals of motion. Their number is enough so that, along with the quadratic constraint, it suffices to scan the entire space of solutions. The latter is revealed to be quite rich, containing cosmological solutions, some of which admit dimensional reduction asymptotically to four dimensions, Kundt spacetimes with vanishing type I (polynomial) curvature scalars and solutions describing periodic universes which behave like cosmological time crystals.

gr-qc↗

arXiv2024

The effects of the pole dark energy on gravitational waves

In this paper, we have studied the effects of pole dark energy on the evolution of gravitational waves. The background evolution of gravitational waves in a flat FRW universe is considered and its dynamics are studied in the presence of pole dark energy. Two different potential functions are considered for the study. Using the field equations, we formulated the perturbed equations governing the evolution of gravitational waves with respect to redshift z within the background of the FRW Universe. Subsequently, we delved into the characteristics of gravitational waves for the pole dark energy model and reached interesting results.

gr-qc↗

arXiv2024

On the entropy corrected thermal features of black holes

In this work, we investigate the thermal properties of black holes using a new class of generalized entropy functions [K. Ourabah, Class. Quantum Grav., 41, 015010 (2024)]. At the fundamental level, these entropic forms are associated with alternative gravitational laws, within an entropic gravity framework. Our investigation revolves around three distinct entropy functions associated with the Yukawa Potential Correction, Non-local Gravity Correction, and Gradient Field Gravity Correction. Through comparative analysis, we study how such entropic constructs impact the thermodynamic behavior of black holes. For each case, we derive the stability thermodynamic conditions associated with the respective entropic constructs.

gr-qc↗

arXiv2022

Thermodynamics of a Schwarzschild-like black hole with a minimum observable length and the radiation process of a thin accretion disc around it

We study quantum gravity effects on the thermodynamic character and the radiation process of the thin accretion disks around Schwarzschild-like black hole. The quantum gravity correction is invoked through the framework of generalization of uncertainty which is equivalent to the renormalization group improved quantum gravity and maintain the limit of the asymptotically safe preposition of gravity. It admits a free parameter that encodes the quantum effects on the spacetime geometry. It allows us to study how the thermal properties of the black hole itself and the the accretion around it disk are modified in the quantum regime. We computed explicitly the entropy, temperature, free energy, and enthalpy of the modified black hole and show its variation with with the free parameter that encodes the quantum effects. We explicitly make estimations of quantum correction to the time averaged energy flux, the temperature of the disk, the differential luminosity, and the conversion efficiency of accreting mass into radiation. We observe a conspicuous shifting of the radius of the innermost stable circular orbit (ISCO) toward small values together with an enhancement of the maximum of the values of the average thermal radiation and greater conversion efficiency of accreting mass into radiation compared to the classical gravity scenario.

gr-qc↗

arXiv2021

Minimal length, maximal momentum and stochastic gravitational waves spectrum generated from cosmological QCD phase transition

We investigate thoroughly the temporal evolution of the universe temperature as a function of the Hubble parameter associated with the Stochastic Gravitational Wave (SGW), that formed at the cosmological QCD phase transition epoch to the current epoch, within the Generalized Uncertainty Principle (GUP) framework. Here we use GUP version which provide constraints on the minimum measurable length and the maximum observable momentum, that characterized by a free parameter $α$. We study the effect of this parameter on the SGW background. We show that the effect can slightly enhance the SGW frequency in the lower frequency regime which might be important in the detection of SGW in the future GW detection facilities.

gr-qc↗

arXiv2021

Generalized uncertainty principle and stochastic gravitational wave background spectrum

This paper concerned with the effect of generalized uncertainty principle (GUP) on the stochastic gravitational wave (SGW) background signal that produced during first order cosmological QCD phase transition in early universe. A modified formula of entropy is used to calculate the temporal evolution of temperature of the universe as a function of the Hubble parameter. The pressure that results from the recent lattice calculations, which provides parameterizations of the pressure due to $u,~d,~s$ quarks and gluons, with trace anomaly is used to describe the equation of state around QCD epoch. A redshift in the peak frequency of SGW at current epoch is calculated. The results indicate an increase in the frequency peak due to GUP effect, which improves the ability to detect it. Taking into account bubble wall collisions (BWC) and turbulent magnetohydrodynamics (MHD) as a source of SGW, a fractional energy density is investigated. It is found that the GUP effect weakens the SGW signal generated during QCD phase transition in comparison to its counterpart in the absence of GUP. These results support understanding the cosmological QCD phase transition and test the effectiveness of the GUP theory.

gr-qc↗

arXiv2020

New Non-commutative and Higher Derivatives Quantum Mechanics from GUPs

We explore a new class of Non-linear GUPs (NLGUP) showing the emergence of a new non-commutative and higher derivatives quantum mechanics. Within it, we introduce the shortest fundamental scale as a UV fixed point in the NLGUP commutators [X, P] = i\hbar f(P), having in mind a fundamental highest energy threshold related to the Planck scale. We show that this leads to lose commutativity of space coordinates, that start to be dependent by the angular momenta of the system. On the other hand, non-linear GUP must lead to a redefinition of the Schrodinger equation to a new non-local integral-differential equation. We also discuss the modification of the Dyson series in time-dependent perturbative approaches. This may suggest that, in NLGUPs, non-commutativity and higher derivatives may be intimately interconnected within a unified and coherent algebra. We also show that Dirac and Klein-Gordon equations are extended with higher space-derivatives according to the NLGUP. We compute momenta-dependent corrections to the dispersion velocity, showing that the Lorentz invariance is deformed. We comment on possible implications in tests of light dispersion relations from Gamma-Ray-Bursts or Blazars, with potential interests for future experiments such as LHAASO, HAWC and CTA.

physics.gen-ph↗

arXiv2015

The minimal length uncertainty and the nonextensive thermodynamics

In this paper, we study the thermodynamics of quantum harmonic oscillator in the Tsallis framework and in the presence of a minimal length uncertainty. The existence of the minimal length is motivated by various theories such as string theory, loop quantum gravity, and black-hole physics. We analytically obtain the partition function, probability function, internal energy, and the specific heat capacity of the vibrational quantum system for $1<q<\frac{3}{2}$ and compare the results with those of Tsallis and Boltzmann-Gibbs statistics without the minimal length scale.

hep-th↗

arXiv2013

Minimal length, maximal momentum and thermodynamics of black body radiation

In this paper we study thermodynamics of black body radiation in the presence of quantum gravitational effects through a Generalized Uncertainty Principle that admits both a minimal measurable length and a maximal momentum. We focus on quantum gravity induced modifications of thermodynamical quantities in this framework. Some important issues such as the generalized Planck distribution, Wien s law and Dulong Petit law are studied in this setup with details.

physics.gen-ph↗

arXiv2013

Statistical mechanics of ideal gas in the presence of minimal length and maximal momentum

Various approaches to quantum gravity suggest that the fundamental volume of the phase space of the given space for representative points, means !0, should be modified. In this paper, we study the effects of this modification on the thermodynamics of an ideal gas within the micro canonical ensemble. For this end, we use a Generalized Uncertainty Principle (GUP) that admits both a minimal measurable length and a maximal momentum. Using this GUP causes decreasing the total number of the microstates of the system. In the first step, we calculate these reductions for classical ideal gas, and in the second step, we calculate these effects for ultra relativistic gas.

physics.gen-ph↗