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M. Bousder

Publications and source records attributed to M. Bousder.

17 recordsLinked to original sources

Klein-Gordon and Schr\"{o}dinger solutions in Lovelock quantum gravity

This study investigates the application of wave functions to explore various solutions of the Klein-Gordon and Schr\"{o}dinger 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% \"{o}dinger equation, with one solution highlighting the influence of the Airy solution on the wave function's evolution over time.

gr-qc

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

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

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 Schr\"{o}dinger 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

A proof of holographic complexity conjecture: wormhole between horizon and singularity

This letter provides evidence of complexity-volume and complexity-action conjectures by examining the structure of a black hole, which comprises a horizon linked to the singularity through a wormhole. In this situation, the shape of the black hole's geometry resembles that of Gabriel's horn. In essence, our results indicate that the information paradox is merely the painter's paradox.

hep-th

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

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

Topological densities in Einstein-scalar-Gauss-Bonnet gravity

The present work is devoted to studying the background dynamical evolution of a scalar field in Einstein-Gauss-Bonnet gravity in maximally symmetric space-time. This study is useful for giving meaning to the presence of two Gauss-Bonnet vacua, instead of using the spherically symmetric bubbles of the "true" vacuum expand in the "false" vacuum. The theory admits two possible effective cosmological constants, which lead to two maximally symmetric vacuum solutions. The first solution corresponds to the dynamics of dark energy. When there is matter, the second solution describes dark matter. In Einstein-Gauss-Bonnet gravity, we establish the expression of the topological mass spectrum which depends on the golden ratio and its inverse. In the Schwarzschild limit, the topological density corresponds to the standard model radiation energy density. We find the mass loss rate which gives the evolution of mass over time.

gr-qc

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 {\omega}_{{\Lambda}} of dark energy in third-order Lovelock gravity. We show that the value "-1" represents a stable equilibrium of {\omega}_{{\Lambda}}.

gr-qc

Interpretation of galaxy rotation curves from primordial black holes in 4D Einstein-Gauss-Bonnet gravity

We develop a novel approach to the dark matter halos in the context of 4 dimensional Einstein--scalar-Gauss-Bonnet gravity to reproduce the flat rotation curves of galaxies. Moreover, the Gauss-Bonnet coupling describes the interior structure of the galaxies, while there is a presence of a scalar field $\phi $ in the galaxy edges. This can provide an interesting interpretation for the functional coupling $f(\phi )$. We discuss how this comparison can naturally drive the observed percentages of matter and dark matter in the Universe. The effective mass range\ in our model is $% 10^{-2}kg-10^{3}kg$, which is in good agreement with the constraints on primordial black holes.

physics.gen-ph

Unitary description of the black hole by prime numbers

In this paper, we study the thermofield double states of doubly-holographic gravity in two copies of the horizons. We show that the asymptotically AdS spacetimes describe an entangled states of a pair of CFTs based on the Farey sequence. We propose a new technique to geometrize the black hole horizon. Our protocol is based on the so-called Farey diagram. We construct states and entropies to describe the unit cells on the horizon. As a result, we have proved that the quantum states on the horizon are encoded by prime numbers. Therefore, we found that the entropy of the code space and area law are writtens in logarithmic form of the prime numbers. We show that the number of connected components of the Farey sequence can build the Fermi--Dirac distribution. To solve the information paradox problem, we find that the Hawking radiation follows geodesic of the Farey diagram, then he turns around and falls on the horizon. Our aim is to show that there is appearance of several Page times, because of discontinuous emission of these radiations. Finally, we mention the possibility to describe the quantum Hall effect by using the Farey diagram. In this paper, we find a link between quantum information and the theory of numbers passing through geometry.

hep-th

Preheating and Reheating Constraints in Supersymmetric Braneworld Inflation

We study the evolution of the Universe at early stages, we discuss also preheating in the framework of hybrid braneworld inflation by setting conditions on the coupling constants $\lambda $ and $g$\ for effective production of $\chi$-particles. Considering the phase between the time observable CMB scales crossed the horizon and the present time, we write reheating and preheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in terms of the scalar spectral index $n_{s}$, and prove that, unlike the reheating case, the preheating duration does not depend on the values of the equation of state $\omega ^{\ast }$. We apply the slow-roll approximation in the high energy limit to constrain the parameters of D-term hybrid potential. We show also that some inflationary parameters, in particular, the spectral index $n_{s}$ demand that the potential parameter $\alpha$ is bounded as $\alpha \geq 1$ to be consistent with $Planck$'s data, while the ratio $r$ is in agreement with observation for $ \alpha \leq 1 $ considering high inflationary e-folds. We also propose an investigation of the brane tension effect on the reheating temperature. Comparing our results to recent CMB measurements, we study preheating and reheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in the Hybrid D-term inflation model in the range $0.8\leq \alpha\leq 1.1$\, and conclude that $T_{re}$ and $N_{re}$ require $\alpha \leq 1$, while for $N_{pre}$ the condition $\alpha \leq 0.9$ must be satisfied, to be compatible with $Planck$'s results.

astro-ph.CO

A new constant behind the rotational velocity of galaxies

The present work is devoted to study the dynamical evolution of the galaxies in scalar-GaussBonnet gravity in relationship with the MOND paradigm. This study is useful for giving meaning to the presence of a new gravitational constant. The stability of dark matter is strongly dependent on matter energy density. We interested in calculating the maximum rotational velocity of galaxies. We show that rotating galaxies can be described by a new parameter which depends on both on the minimum value of scalar fields and the effective mass of this field. According to the observation data, we have shown that this parameter is a constant.

gr-qc

Charged 4D Einstein-Gauss-Bonnet Black Hole: Vacuum solutions, Cauchy Horizon, Thermodynamics

In this paper, we investigate the four-dimensional Einstein-Gauss-Bonnet black hole. The thermodynamic variables and equations of state of black holes are obtained in terms of a new parameterization. We discuss a formulation of the van der Waals equation by studying the effects of the temperature on P-V isotherms. We show the influence of the Cauchy horizon on the thermodynamic parameters. We prove by different methods, that the black hole entropy obey area law (plus logarithmic term that depends on the Gauss-Bonnet coupling {\alpha}). We propose a physical meaning for the logarithmic correction to the area law. This work can be extended to the extremal EGB black hole, in that case, we study the relationship between compressibility factor, specific heat and the coupling {\alpha}.

gr-qc

Particle-antiparticle in 4D charged Einstein-Gauss-Bonnet black hole

We study the charge of the 4D-Einstein-Gauss-Bonnet black hole by a negative charge and a positive charge of a particle-antiparticle pair on the horizons r- and r+, respectively. We show that there are two types of the Schwarzschild black hole. We show also that the Einstein-Gauss-Bonnet black hole charge has quantified values. We obtain the Hawking-Bekenstein formula with two logarithmic corrections, the second correction depends on the cosmological constant and the black hole charge. Finally, we study the thermodynamics of the EGB-AdS black hole.

gr-qc

Quantum f(R) gravity and AdS/CFT

We propose to study the entanglement entropy in braneworld modified gravity. We show that the $d+1$-dimensional action $I_{d+1}$ is the dual of $d-1$% -dimensional entanglement entropy $S_{d-1}^{EE}$. Moreover, we remark that the generalization of action-entropy shows us a new form of $f(R)$ gravity which is in good agreement with the most choices of $f(R)$ gravity in the literature. We show also that there are two copies of the AdS spaces in holographic entanglement $f(R)$ gravity. We have proposed that the time is a holographic projection of the hidden $d$-brane on the visible $d$-brane. To determine the geometry of this holographic projection, we have used the $% AdS_{2}$ geometry of the black hole. Namely, the past of events is memorized over an $\mathbb{S}^{1}$. We show that the time projection is a stereographic projection from a time sphere $\mathbb{S}^{d-2}$ on the hidden $d$-brane to the visible $d$-brane. We suggest that there is a difference between the time in classical gravity and the time in quantum gravity.

hep-th

A new unified model of dark matter and dark energy in 5-dimensional $f(R,\phi)$ gravity

We propose a new unified model that describes~dark energy and dark matter in the context of $f(R,\phi )$ gravity using a massive scalar field in five dimensions. The scalar field is considered in the bulk that surrounds the 3-brane in branworld model. We show that for a specific choice of the $% f(R,\phi )$ function, we can describe the Einstein gravitation in 4-dimensional space-time. We obtain a relationship between the speed of the universe's expansion and the speed of the bulk's expansion. We also propose that the dark matter is represented by the scalar field mass and that the dark energy is a kinetic energy of this field. Finally, we show that, according to conditions, one can obtain the percentages of density\ of dark matter and the density of ordinary matter.

gr-qc