Showing papers in "Canadian Journal of Physics in 2013"

Bound state solutions of the Manning-Rosen potential

Abstract: Using the asymptotic iteration method (AIM), we have obtained analytical approximations to the l-wave solutions of the Schrodinger equation with the Manning–Rosen potential. The energy eigenvalues equation and the corresponding wavefunctions have been obtained explicitly. Three different Pekeris-type approximation schemes have been used to deal with thecentrifugal term. To show the accuracy of our results, we have calculated the eigenvalues numerically for arbitrary quantumnumbers n and l for some diatomic molecules (HCl, CH, LiH, and CO). It is found that the results are in good agreement with other results found in the literature. A straightforward extension to the s-wave case and Hulthen potential case are also presented.

Finite-time future singularities models in $f(T)$ gravity and the effects of viscosity

Abstract: We investigate models of future finite-time singularities in $f(T)$ theory, where $T$ is the torsion scalar. The algebraic function $f(T)$ is put as the teleparallel term $T$ plus an arbitrary function $g(T)$. A suitable expression of the Hubble parameter is assumed and constraints are imposed in order to provide an expanding universe. Two parameters $\beta$ and $H_s$ that appear in the Hubble parameter are relevant in specifying the types of singularities. Differential equations of $g(T)$ are established and solved, leading to the algebraic $f(T)$ models for each type of future finite time singularity. Moreover, we take into account the viscosity in the fluid and discuss three interesting cases: constant viscosity, viscosity proportional to $\sqrt{-T}$ and the general one where the viscosity is proportional to $(-T)^{n/2}$, where $n$ is a natural number. We see that for the first and second cases, in general, the singularities are robust against the viscous fluid, while for the general case, the Big Rip and the Big Freeze can be avoided from the effects of the viscosity for some values of $n$.

Finite-time singularities in f(R, T) gravity and the effect of conformal anomaly

Abstract: We investigate $f(R,T)$ gravity models ($R$ is the curvature scalar and $T$ is the trace of the stress-energy tensor of ordinary matter) that are able to reproduce the four known types of future finite-time singularities. We choose a suitable expression for the Hubble parameter in order to realise the cosmic acceleration and we introduce two parameters, $\alpha$ and $H_s$, which characterise each type of singularity. We address conformal anomaly and we observe that it cannot remove the sudden singularity or the type IV one, but, for some values of $\alpha$, the big rip and the type III singularity may be avoided. We also find that, even without taking into account conformal anomaly, the big rip and the type III singularity may be removed thanks to the presence of the $T$ contribution of the $f(R,T)$ theory.

STU–QCD correspondence

Abstract: In this review article we consider a special case of D = 5, N=2 supergravity called the STU model. We apply the gauge–gravity correspondence to the STU model to gain insight into properties of the quark–gluon plasma. Given that the quark–gluon plasma is in reality described by quantum chromodynamics (QCD), we call our study STU–QCD correspondence. First, we investigate the thermodynamics and hydrodynamics of the STU background. Then we use a dual picture of the theory, which is type IIB string theory, to obtain the drag force and jet-quenching parameter of an external probe quark.

Reconstruction of f(T) and f(R) gravity according to (m, n)-type holographic dark energy

Abstract: Motivated by earlier works (Wu and Zhu. Phys. Lett. B, 660, 293 (2008); Daouda et al. Eur. Phys. J. C, 72, 1893 (2012)), we extend them by considering a newly proposed model of (m, n)-type holographic dark energy in f(R) and f(T) gravity theories, where R and T represent Ricci scalar and torsion scalar respectively. Specifically, we reconstruct the two later gravity models and discuss their viability and cosmography. The obtained gravity models are free from ghosts, consistent with local solar system tests, and describe effective positive gravitational constant.

Two-dimensional Duffin–Kemmer–Petiau oscillator under an external magnetic field

Abstract: The eigensolutions of massive spin-0 and spin-1 particles of a Dirac oscillator in an external magnetic field, both in the commutative and noncommutative space, are found by using the Duffin–Kemmer–Petiau equation. The solutions in both cases are obtained using the parametric generalization of the Nikiforov–Uvarov method.

Holographic, new agegraphic, and ghost dark energy models in fractal cosmology

Abstract: We investigate the holographic, new agegraphic, and ghost dark energy models in the framework of fractal cosmology. We consider a fractal flat Friedmann–Robertson–Walker universe filled with dark energy and matter. We obtain the deceleration and equation of state parameters of the selected dark energy models in the ultraviolet regime and discuss their implications in the early universe.

A reconstruction of modified holographic Ricci dark energy in f(R, T) gravity

Abstract: In this paper, we consider a recently proposed model of dark energy (DE) know as modified holographic Ricci DE (which is function of the Hubble parameter and its first derivative with respect to cosmic time, t) in light of the f(R, T) model of modified gravity, considering the particular model f(R, T) = μR + νT, with μ and ν constants. The equation of state parameter ωΛ approaches but never reaches the value −1, implying a quintessence-like behavior of the model. The deceleration parameter q passes from decelerated to accelerated phase at a redshift of z ≈ 0.2, showing also a small dependence from the values of the parameters considered. Thanks to the statefinder diagnostic analysis, we observed that the ΛCDM phase for the considered model is attainable. We observed that the fractional energy densities for DE and dark matter, ΩΛ and Ωm, have an increasing and a decreasing pattern, respectively, with the evolution of the universe, indicating an evolution from matter to DE dominated universe. Finally, study...

Noether gauge symmetry of modified teleparallel gravity minimally coupled with a canonical scalar field

Abstract: This paper is devoted to the study of Noether gauge symmetries of f(T) gravity minimally coupled with a canonical scalar field. We explicitly determine the unknown functions of the theory: f(T), V(ϕ), and W(ϕ). We have shown that there are two invariants for this model, one of which defines the Hamiltonian, H, under time invariance (energy conservation) and the other is related to scaling invariance. We show that the equation of state parameter in the present model can cross the cosmological constant boundary. The behavior of the Hubble parameter in our model closely matches to that of the ΛCDM model, thus our model is an alternative to the latter.

MHD mixed convection flow of a viscoelastic fluid over an inclined surface with a nonuniform heat source/sink

Abstract: The steady mixed convection boundary layer flow over an inclined stretching surface immersed in an incompressible viscoelastic fluid is considered in this paper. Employing suitable similarity transformations, the governing partial differential equations are transformed into ordinary differential equations, and the transformed equations are solved numerically using Runge–Kutta–Fehlberg method. Herein, two different types of heating processes are considered, namely, (i) prescribed surface temperature and (ii) prescribed wall heat flux. The effects of the governing parameters on the flow field and heat transfer characteristics are obtained and discussed. It is found that velocity decreases and temperature increases with an increase in the value of angle of inclination.

Le troisième coefficient du viriel du gaz de Bose unitaire

Abstract: Nous entendons par gaz de Bose unitaire un systeme compose de bosons sans spin interagissant dans l'onde s par un potentiel de longueur de diffusion infinie et de portee (reelle ou effective) presque negligeable, systeme pour l'instant abstrait mais dont la tentative de realisation avec des atomes froids est en cours. A partir de la solution analytique connue du probleme a trois corps dans un piege harmonique, et de methodes precedemment developpees pour des fermions, nous determinons le troisieme cumulant b3, puis le troisieme coefficient du viriel a3 de ce gaz, dans le cas spatialement homogene, en fonction de sa temperature et du parametre a trois corps Rt caracterisant l'effet Efimov. Un point marquant est qu'en convertissant des series en des integrales (par une methode des residus inverse), puis en utilisant un petit parametre inattendu, l'angle de masse ν = π/6 des trois bosons, on peut pousser l'estimation completement analytique de b3 et de a3 jusqu'a une erreur en pratique negligeable.

Nonstandard fractional exponential Lagrangians, fractional geodesic equation, complex general relativity, and discrete gravity

Abstract: Nonstandard Lagrangians are generating functions of different equations of motion. They have gained increasing importance in many different fields. In fact, nonstandard Lagrangians date back to 1978, when Arnold entitled them "non- natural" in his classic book, Mathematical Methods of Classical Mechanics (Springer, New York. 1978). In applied mathematics, most dynamical equations can be obtained by using generating Lagrangian functions (e.g., power-law and exponential Lagrangians), which has been shown by mathematicians, who have also demonstrated that there is an infinite number of such functions. Besides this interesting field, the topic of fractional calculus of variations has gained growing importance because of its wide application in different fields of science. In this paper, we generalize the fractional actionlike variational approach for the case of a nonstandard exponential Lagrangian. To appreciate this new approach, we explore some of its main consequences in Einstein's general relativity. Some results are revealed and discussed accordingly mainly the transition from general relativity to complex relativity and emergence of a discrete gravitational coupling constant.

Multiconfigurational Dirac–Fock energy levels and radiative rates for Br-like tungsten

Abstract: Energies, lifetimes, and wavefunction compositions have been computed for all levels of odd parity 4s24p5 ground configuration and 3d94s24p6 excited configuration as well as 4s4p6 and 4s24p44d even parity excited configurations in highly charged Br-like tungsten ion (W XL) by using the multiconfigurational Dirac–Fock method. Also, we have reported the transition wavelengths, oscillator strengths, transition probabilities and line strengths for the electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transition from the 4s24p5 configuration. We have compared our calculated results with the other available experimental and theoretical results. The excellent agreement observed between our new results and those obtained using different approaches confirm the quality of our results.

Tensor coupling and relativistic spin and pseudospin symmetries with the Hellmann potential

Abstract: The Hellmann potential is a superposition potential that consists of an attractive Coulomb potential −a/r and Yukawa potential be −δr/r. By using the generalized parametric Nikiforov–Uvarov method,...

The impact theory of spectral line shapes: a paradigm shift1

Abstract: An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, a...

Fermion tunneling for traversable wormholes

Abstract: Hawking radiation can be interpreted as a quantum phenomenon of particles tunneling through black hole horizons. In this formulation, Kerner and Mann analyzed fermions emission via tunneling and investigated tunneling probabilities related to the Hawking temperature. This paper is devoted to the use of the Kerner and Mann technique for axially symmetric slowly rotating wormholes. We calculate tunneling probability for outgoing (as well as incoming) charged fermions and obtain their respective Hawking temperatures at horizon radii and also explore their graphical pictures.

Isgur–Wise function within a QCD quark model with Airy's function as the wave function of heavy–light mesons

Abstract: We report a somewhat improved wave function for mesons by taking the linear confinement term in standard QCD potential as a parent and the coulombic term as a perturbation while applying quantum me...

Solvent effect on the dipole moments and photo physical behaviour of 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene dye

Abstract: The absorption and emission spectra of fluorescent thiophene dye, namely, 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene, have been recorded at room temperature in solvents of different polarities. The excited state dipole moments ( e) were estimated from Lippert’s, Bakhshiev’s, and Kawski–Chamma–Viallet’s equations using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The optimized geometry of themolecule and gwere calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The g and ewere calculated bymeans of solvatochromic shift method and ewas determined in combination with g. It was observed that ewere higher than those of the g, indicating a substantial redistribution of the -electron densities in a more polar excited state for the selected thiophene dye. Further, the change in the dipole moment ( ) was calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter ET N and values are compared. PACS Nos.: 33.50.−j, 87.64.i, 31.70.Hq, 87.15.kg. Resume : Nous avons enregistre, a la temperature de la piece et dans des solvants de differentes polarites, les spectres d’absorption et d’emission du colorant thiophene fluorescent 2,5-di-(5-tertbutyl-benzoxazolyl). Nous estimons le moment dipolaire ( e) des etats excites a partir des equations de Bakhshiev et Kawski–Chamma–Viallet en utilisant la variation du deplacement de Stokes, avec la constante dielectrique du solvant et l’indice de refraction. La geometrie de lamolecule est completement optimisee et nous calculons g a l’aide du logiciel Gaussian 03 utilisant le modele theorique B3LYP/6-31g*. Les parametres g et e sont calcules par lamethode du deplacement solvatochromique et e est determine en combinaison avec g. Nous observons que les valeurs de e sont plus elevees que celles de g, ce qui indique une redistribution substantielle des densites d’electrons dans un etat excite plus polaire pour le colorant thiophene choisi. De plus, nous evaluons les changements dumoment dipolaire ( ) a partir de deux methodes, celle du deplacement solvatochromique et sur la base d’un parametre de polarite empirique microscopique ET N et nous comparons ensuite les resultats. [Traduit par la Redaction]

Some late-time cosmological aspects of a Gauss–Bonnet gravity with nonminimal coupling à la Brans–Dicke: solutions and perspectives

Abstract: In this paper, we study modified homogeneous and isotropic cosmological models based on the Gauss–Bonnet invariant term as models of an accelerating universe. We discuss and criticize the late-time dynamics of six independent cosmological models: in the first model, we discuss the case of the modified gravity f(R) ∝ R1+δ for δ = −1/2 and 1 augmented by the Gauss–Bonnet invariant term; in the second model, we discuss the general case of f(R) ∝ R1+δ accompanied by a nonminimal coupling between the scalar field and the Ricci curvature as well as the Gauss–Bonnet invariant; in the third model, we discuss a generalized modified gravity model that includes the Einstein–Hilbert action, a dynamical cosmological constant, and an effective gravitational coupling constant; in the fourth model, we discuss a more generalized modified scalar–tensor cosmology that includes in addition to the Gauss–Bonnet invariant term, stringy corrections motivated from string and heterotic superstring arguments; in the fifth model, we...

Makarov potential in relativistic equation via Laplace transformation approach

Abstract: Exact solutions and corresponding normalized eigenfunctions of the Dirac equation are studied for the Makarov potential by using the Laplace transform approach under the pseudospin symmetry. By using the ideas of SUSY and shape invariance, we obtain the energy eigenvalues equation. The wave functions of the angle part are obtained by using the Nikiforov–Uvarov method, too. Finally, we also discuss the special cases of this potential and the valence energy states can be produced from our solution for the hole state by taking appropriate transformation of parameters.

A study on the modified holographic Ricci dark energy in logarithmic f(T) gravity

Abstract: In this paper, we have studied and investigated the behavior of a modified holographic Ricci dark energy (DE) model interacting with pressureless dark matter (DM) under the theory of modified gravity, dubbed logarithmic f(T) gravity. We have chosen the interaction term between DE and DM in the form Q = 3γHρm and investigated the behavior of the torsion, T, the Hubble parameter, H, the equation of state parameter, ωDE, the energy density of DE, ρDE, and the energy density contribution due to torsion, ρT, as functions of the redshift, z. We have found that T increases with the redshift, z, H increases with the evolution of the universe, ωDE has a quintessence-like behavior, and both energy densities increase going from higher to lower redshifts.

Obliquely propagating dust-ion acoustic solitary waves and their multidimensional instabilities in magnetized dusty plasmas with bi-maxwellian electrons

Abstract: The nonlinear propagation of dust-ion acoustic (DIA) waves in an obliquely propagating magnetized dusty plasma, consisting of bi-maxwellian electrons (namely lower and higher temperature maxwellian electrons), negatively charged immo- bile dust grains, and inertial ions is rigorously investigated by deriving the Zakharov-Kuznetsov equation. Later, the multidi- mensional instability of the DIA solitary waves (DIASWs) is analyzed using the small-k perturbation technique. It is investigated that the nature of the DIASWs, the instability criterion, and the growth rate of the perturbation mode are significantly modified by the external magnetic field and the propagation directions of both the nonlinear waves and their perturbation modes. The implications of the results obtained from this investigation in space and laboratory dusty plasmas are briefly discussed.

Dark energy and viscous cosmology with variable G and Λ in an anisotropic background

Abstract: The general Bianchi type I with dark energy in the form of standard and modified Chaplygin gas with variable G and Λ and bulk viscosity have been investigated. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models that reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe, that which yields a constant value for the deceleration parameter. We reconstruct bulk viscosity, ξ, gravitational parameter, G, cosmological term, Λ, density parameter, Ω, cosmological constant density parameter, ΩΛ, and deceleration parameter, q, for different equations of state. In the large time limit the model describes an accelerating universe wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pres...

Role of the nonlocality of the vector potential in the Aharonov-Bohm effect

Abstract: When the electromagnetic potentials are expressed in the Coulomb gauge in terms of the electric and magnetic fields rather than the sources responsible for these fields they have a simple form that is nonlocal (i.e., the potentials depend on the fields at every point in space). It is this nonlocality of classical electrodynamics that is primarily responsible for the puzzle associated with the static Aharonov-Bohm effect: that its interference pattern is affected by fields in a region of space that the electron beam never enters.

Massless fermion quasinormal modes in the Horava-Lifshitz background

Abstract: In this paper we consider the Horava–Lifshitz background and obtain the massless fermion quasinormal modes. In that case we use the Newman–Penrose formalism and the massless Dirac equation to calculate the radial and angular parts of equations. The wave function and corresponding modes can be obtained using the factorization method.

Collision-induced spectra and current astronomical research1

Abstract: Collision-induced spectra are the spectra of complexes of two or more atoms or molecules in a “fly-by” collisional encounter. Collision-induced absorption (CIA) has been observed in many dense gases and gas mixtures, in most cases at infrared frequencies in the form of quasi continua, and also in liquids and solids. CIA spectra of several binary complexes have been computed using modern quantum chemical methods, combined with molecular scattering theory, which couples the collisional complex to the radiation field as usual in other spectroscopic work. Binary collisional systems, such as H2 interacting with another H2 molecule, or with a helium or hydrogen atom, are first candidates for such computational work, owing to their small number of electrons and the astrophysical interest in such systems. The computed CIA spectra are found to be in close agreement with existing laboratory measurements of such spectra. Laboratory measurements exist at a limited selection of temperatures around 300 K and lower, but...

Exact solution of the unsteady Krook kinetic model and nonequilibrium thermodynamic study for a rarefied gas affected by a nonlinear thermal radiation field

Abstract: A development of the previous paper (J. Non-Equilib. Thermodyn. 36, 75 (2011)) is introduced. The nonstationary Krook kinetic equation model for a rarefied gas affected by nonlinear thermal radiation field is solved, instead of the stationary equation. In a frame comoving with the fluid, analytically the Bhatnager–Gross–Krook model kinetic equation is applied. The travelling wave solution method is used to get the exact solution of the nonlinear partial differential equations. These equations were produced from applying the moment method to the unsteady Boltzmann equation. Now we should solve nonlinear partial differential equations in place of nonlinear ordinary differential equations, which represent an arduous task. The unsteady solution gives the problem a great generality and more applications. The new problem is investigated to follow the behavior of the macroscopic properties of the gas, such as the temperature and concentration. They are substituted into the corresponding two-stream maxiwallian di...

Fluorescence quenching of 6BDTC by aniline in different solvents1

Abstract: Quenching mechanisms of coumarin derivative 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) were carried out in different solvents using the steady-state method to understand the role of diffusion in the quenching mechanism. The solute was excited by UV radiation of wavelength 360 nm. Various quenching parameters like frequency of encounter, kd; probability of quenching per encounter, p; and quenching rate parameter, kq, were experimentally determined for all solvents. Activation energies of quenching, Ea, were also determined by using the literature values of activation energy of diffusion, Ed. It was found that the values of Ea were less than Ed in all solvents indicating that the quenching reactions are more significantly influenced by material diffusion.

Thermodynamics of charged Newman–Unti–Tamburino accelerating rotating black holes

Abstract: This paper is devoted to studying the thermodynamics of charged Newman–Unti–Tamburino black hole solutions to the field equations, including rotation and acceleration. We evaluate some thermodynami...

Coupled quantum oscillators within independent quantum reservoirs

Abstract: This paper addresses the problem of open quantum systems. The energy of interaction of coupled dissipative systems is the main focus of the study. Quantum Langevin equations for two quantum couplin...