Searcharxiv⌕ Search

arXiv subjects

H. Ez-Zahraouy

Publications and source records attributed to H. Ez-Zahraouy.

At least 19 recordsLinked to original sources
arXiv2024

Klein-Gordon and Schrödinger solutions in Lovelock quantum gravity

This study investigates the application of wave functions to explore various solutions of the Klein-Gordon and Schrödinger equations within the framework of Lovelock gravity. We also present the derived Smarr formula from the topological density. The Klein-Gordon solution leads to the Wheeler-de Witt Hamiltonian and quasinormal modes, and we demonstrate the connection between the potential and the black hole temperature within the Schwarzschild limit. Additionally, we discuss different solutions of the Schr% ödinger equation, with one solution highlighting the influence of the Airy solution on the wave function's evolution over time.

gr-qc↗
arXiv2024

Hopfions of massive gauge bosons in early universe

This letter presents a novel model that characterizes the curvature of space-time, influenced by a massive gauge field in the early universe. This curvature can lead to a multitude of observations, including the Hubble tension issue and the isotropic stochastic gravitational-wave background. We introduce, for the first time, the concept of gauge field Hopfions, which exist in the space-time. We further investigate how hopfions can influence Hubble parameter values. Our findings open the door to utilizing hopfions as a topological source which links both gravitation and the gauge field.

gr-qc↗
arXiv2023

Pulsar timing array results sheds light on Hubble tension during the end of inflation

Recently, pulsar timing array (PTA) collaborations, including NANOGrav, have reported evidence of a stochastic gravitational wave background within the nHz frequency range.\ It can be interpreted by gravitational waves from preheating era. In this context, we demonstrate that the emission of this stochastic gravitational wave background can be attributed to fluctuations occurring at the end of inflation, thus giving rise to the Hubble tension issue. At the onset of inflation, the value of the frequency of the gravitational wave signal stood at $f=0.08nHz$, but it rapidly transitioned to $f=1nHz$ precisely at the end of inflation. However, just before the end of inflation, a phase characterized by curvature perturbation is known to occur, causing a swift increase in the frequency.

astro-ph.CO↗
arXiv2023

Cosmic acceleration in Lovelock quantum gravity

This paper introduces novel solutions for inflation and late-time cosmic acceleration within the framework of quantum Lovelock gravity, utilizing Friedmann equations. Furthermore, we demonstrate the hypergeometric states of cosmic acceleration through the Schrödinger stationary equation. A physical interpretation is proposed, whereby the rescaled Lovelock couplings represent a topological mass that characterizes the Lovelock branch. This research holds the potential for an extension into the quantum description. Predictions for the spectral tilt and tensor-to-scalar ratio are depicted through plotted curves. By utilizing the rescaled Hubble parameter, the spectral index is determined in terms of the number of e-folds.

gr-qc↗
arXiv2023

Implications of the NANOGrav results for primordial black holes and Hubble tension

The purpose of this work is to investigate the formation and evaporation of the primordial black holes in the inflationary scenarios. Thermodynamic parameters such as mass, temperature and entropy are expressed in terms of NANOGrav frequency. By numerical calculations we show that the constraint on the mass range $10^{-5}kg-10^{50}kg$ is well confirmed. We discuss the relation between the redshift and the probability for gravitational wave source populations. A new parameter associated with the frequency and Hubble rate is presented, by which for the spectral index $n_{s}\approx 0.996$ and the Hubble constant $H_{0}\approx 67.27km.s^{-1}.Mpc^{-1}$, the effective Hubble constant is calculated to be $H_{eff,0}\approx 73.24km.s^{-1}.Mpc^{-1} $ which is compatible with the observational data. We make a comparison between the Hubble tension and the primordial perturbations and the expression of the mass loss rate, chemical potential and central charge needed to describe the Hawking evaporation will be established.

gr-qc↗
arXiv2023

Entropy as logarithmic term of the central charge and modified Friedmann equation in AdS/CFT correspondence

This paper is about the extended thermodynamics of AdS black holes and its relation to CFT thermodynamics. The logarithmic term of the central charge is interpreted as black hole entropy. We have obtain a modified Friedmann equation from the Smarr formula. We find that the AdS radius is the critical shadow radius. We obtain the Hawking-Bekenstein formula with logarithmic corrections, which depends on the central charge. The real gas in AdS is a dual of an ideal gas in CFT. This work can be extended to the AdS-Kerr black holes.

gr-qc↗
arXiv2023

Holographic dark energy satisfying the energy conditions in Lovelock gravity

In this paper, we show that the holographic dark energy density hides in the solutions of Lovelock gravity for black holes. Using the obtained mass and temperature we find density equations. We propose a physical interpretation of the rescaled Lovelock couplings as a topological mass that describes the Lovelock branch. In addition to this, we present new solutions that satisfy the energy conditions according to the Lovelock coupling and the horizon curvatures. This work can be extended to the equation of the state ω_{Λ} of dark energy in third-order Lovelock gravity. We show that the value "-1" represents a stable equilibrium of ω_{Λ}.

gr-qc↗
arXiv2020

Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound

The structural, electronic and magnetic properties of Fe7S8 material have been studied within the framework of the ab-initio calculations, the mean field approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin σ=5/2 are the most probable configurations. A mixed Ising model with ferromagnetic spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has been used to study the magnetic properties of this compound. We demonstrated that the magnetic phase transition can be either of the first or of the second order, depending on the value of the exchange interaction and crystal field. The presence of vacancies in every second iron layer leads to incomplete cancellation of magnetic moments, hence to the emergence of the ferrimagnetism. Anomalies in the magnetization behavior have been found and compared with the experimental results.

cond-mat.mtrl-sci↗
arXiv2020

Study of the Ashkin Teller model with spins $S$ = $1$ and $σ$ = $3/2$ subjected to different crystal fields using the Monte-Carlo method

Using the Monte-Carlo method, we study the magnetic properties of the Ashkin-Teller model (ATM) under the effect of the crystal field with spins $S = 1$ and $σ= 3/2$. First, we determine the most stable phases in the phase diagrams at temperature $T = 0$ using exact calculations. For higher temperatures, we use the Monte-Carlo simulation. We have found rich phase diagrams with the ordered phases: a Baxter $3/2$ and a Baxter $1/2$ phases in addition to a $\left\langle σS\right\rangle$ phase that does not show up either in ATM spin 1 or in ATM spin $3/2$ and, lastly, a $\left\langle σ\right\rangle = 1/2$ phase with first and second order transitions.

cond-mat.stat-mech↗
arXiv2005

Phase diagrams in the Blume-Emery-Griffiths Ising films

We study the spin-1 Ising model with bilinear and biquadratic exchange interactions and single-ion crystal field. In addition to the four usual phases: disordered DIS, ferromagnetic FER, antiquadrupolar AQU and ferrimagnetic FRI, we found three new phases in the case of a thin magnetic film, namely: the sublattice A non magnetic phase NMA, the sublattice B non magnetic phase NMB and the global non magnetic phase NMG. These phases are studied, for each layer of the film, either in the temperature-crystal field plane $(T,Δ)$ or in the biquadratic coupling-crystal field plane $(d,Δ)$, for diferent film thicknesses. On the other hand, the thermal behaviour of the layer quadrupolar moments $q_{A}, q_{B}$ and layer magnetisations $m_{A}, m_{B}$ are investigated for negative values of the biquadratic coupling and crystal field. It is also found that for fixed values of the biquadratic coupling, the temperature and the crystal field, each layer of the film can belong to a differnt phase. To illustrate this situation, an example is given for $d=-3.0$, $Δ=-3.0$ and $T=1.3$.

cond-mat.stat-mech↗
arXiv2005

Effect of the inhomogeneity of substrate on layering transitions

We study the surface substrate inhomogeneity effect on the wetting of a spin-1/2 Ising ferromagnetic film in an external magnetic field $H$, using Monte Carlo simulations. It is found the inhomogeneity leads to the formation of islands of positive spins in each layer. However, depending on the values of $H$, for a fixed surface magnetic field $H_s$, each layer exhibits three different phases; totally wet, nonwet and partially wet (PW). In the latter case, we show the existence of three distinct configurations namely: A configuration (PWTD) in which the layer is partially wet with a total disconnection between islands; (PWPD) a configuration in which the layer is partially wet with a partial disconnection between islands; (PWTC) a configuration in which the layer is partially wet and the islands are totally connected. Furthermore, we show that an increase of $H_s$ values breaks the bonds connecting some islands of the phase (PWTC) which leads to an expansion of the (PWPD) region. On the other hand, the frequency distribution and the mean size of island are investigated in the (PWTD) region for fixed values of temperature $T$, $H_s$ and $H$. Moreover, we show the existence of 3D-islands resulting from the formation of islands in each layer.

cond-mat.mtrl-sci↗
arXiv2005

The Effect Of Delay Times On The Optimal Velocity Traffic Flow Behavior

We have numerically investigated the effect of the delay times $τ_f$ and $τ_s$ of a mixture of fast and slow vehicles on the fundamental diagram of the optimal velocity model. The optimal velocity function of the fast cars depends not only on the headway of each car but also on the headway of the immediately preceding one. It is found that the small delay times have almost no effects, while, for sufficiently large delay time $τ_s$ the current profile displays qualitatively five different forms depending on $τ_f$, $τ_s$ and the fractions $d_f$ and $d_s$ of the fast and slow cars respectively. The velocity (current) exhibits first order transitions at low and/or high densities, from freely moving phase to the congested state, and from congested state to the jamming one respectively accompanied by the existence of a local minimal current. Furthermore, there exist a critical value of $τ_f$ above which the metastability and hysteresis appear. The spatial-temporal traffic patterns present more complex structure

cond-mat.other↗
arXiv2005

Surface Effects On Wetting and Layering Transitions

Wetting phenomena plays an interesting role in the technological development of materials. Recently, much attention has been directed to the study of magnetic solid films. To understand, theoretically, the effect of surface on wetting and layering transitions in these systems, we will give in this chapter a presentation of several relevant recent theoretical works realized on wetting and layering transitions in which we explain how the nature of surface can affect the behavior of wetting and layering transitions. Using different spin systems models and different numerical and approximate methods such as mean field and effective field theories, real space renormalization group technique, transfer matrix method and Monte-Carlo simulations, it is found that the wetting and layering transitions depend on the nature of the surface magnetic field, the surface coupling strength, the surface crystal field, the geometry of surface, the in-homogeneity of substrate and the quantum fluctuations at the surface�

cond-mat.mtrl-sci↗
arXiv2004

Blume-Emery-Griffiths Model in a Random Transverse Field

The effect of the random quantum transverse field $Ω$ on the tricritical behavior of the spin-1 Blume- Emery- Griffiths (BEG) model is studied using effective field theory. It is found, that the tricritical behavior depends on both the biquadratic interaction $K$, single- ion anisotropy $Δ$, and the concentration $p$ of the disorder of $Ω$. Indeed, there exist a special value $p_{1}$ of the probability $p$ below which the tricritical behavior disappears.

cond-mat.dis-nn↗
arXiv2004

A Monte Carlo study of random surface field effect on layering transitions

The effect of a random surface field, within the bimodal distribution, on the layering transitions in a spin-1/2 Ising thin film is investigated, using Monte Carlo simulations. It is found that the layering transitions depend strongly on the concentration $p$ of the disorder of the surface magnetic field, for a fixed temperature, surface and external magnetic fields. Indeed, the critical concentration $p_c(k)$ at which the magnetisation of each layer $k$ changes the sign discontinuously, decreases for increasing the applied surface magnetic field, for fixed values of the temperature $T$ and the external magnetic field $H$. Moreover, the behaviour of the layer magnetisations as well as the distribution of positive and negative spins in each layer, are also established for specific values of $H_s$, $H$, $p$ and the temperature $T$. \\

cond-mat.stat-mech↗
arXiv2004

The effect of mixture lenghts of vehicles on the traffic flow behavior in one-dimensional cellular automaton

The effect of mixture lengths of vehicles on the asymmetric exclusion model is studied using numerical simulations for both open and periodic boundaries in parallel dynamics. Densities are calculated as a function of the injecting rates $\alpha1$ and $\alpha2$ of vehicles type 1 and type 2 respectively, and the phase diagram ($\alpha1$,$\alpha2$) is presented for a fixed value of the extracting rate $β$. In this case the first order transition from low to high density phases occurs at $\alpha1+\alpha2=β$ and disappears for $\alpha2>β$. While, in the case of one entry the gap which is a characteristic of the first order transition vanishes with increasing $α$ for n $\neq 0$.However, the first order transition between high and low densities exhibit an end point above which the global density undergoes a continuous passage. The end point coordinate depends strongly on the value of n. In the periodic boundaries case, the presence of vehicles type2 in the chain leads to a modification in the fundamental phase diagram (current, density). Indeed, the maximal current value decreases with increasing the concentration of vehicles type 2, and occurs at higher values of the global density in contrast with what was found by Schadschneider et al \cite{20}.

cond-mat.stat-mech↗
arXiv2003

Monte Carlo Study of Order-Disorder Layering Transitions in the Blume-Capel Model

The order-disorder layering transitions, of the Blume-Capel model, are studied using the Monte Carlo (MC) simulations, in the presence of a variable crystal field. For a very low temperature, the results are in good agreement with the ground state study. The first order transition line, found for low temperatures, is connected to the second order transition line, seen for higher temperatures, by a tri-critical point, for each layer. The reentrant phenomena, caused by a competition of thermal fluctuations and an inductor magnetic field created by the deeper layers, is found for the first $k_0$ layers from the surface, where $k_0$ is exactly the number of layering transitions allowed by the ground state study. The layer magnetizations $m_k$, the magnetic susceptibilities $χ_{m,k}$ and the quadrupolar magnetic susceptibilities $χ_{q,k}$ and the corresponding critical exponent, for each layer $k$, are also investigated.

cond-mat.soft↗