Showing papers in "European Physical Journal Plus in 2013"

Performance of the ALICE Time-Of-Flight detector at the LHC

Abstract: The Time-Of-Flight (TOF) detector of the ALICE experiment at the CERN LHC is based on Multi-gap Resistive Plate Chambers (MRPCs) technology. During the 2009-2013 data taking the TOF system had very stable operations with a total time resolution of 80ps. Details of the different calibration procedures and performance with data from collisions at the LHC will be described.

Simulations: The dark side

Abstract: This paper discusses the Monte Carlo and Molecular Dynamics methods. Both methods are, in principle, simple. However, simple does not mean risk-free. In the literature, many of the pitfalls in the field are mentioned, but usually as a footnote --and these footnotes are scattered over many papers. The present paper focuses on the “dark side” of simulation: it is one big footnote. I should stress that “dark”, in this context, has no negative moral implication. It just means: under-exposed.

Numerical solution for boundary layer flow due to a nonlinearly stretching sheet with variable thickness and slip velocity

Abstract: This article presents a numerical solution for the flow of a Newtonian fluid over an impermeable stretching sheet with a power law surface velocity, slip velocity and variable thickness. The flow is caused by a nonlinear stretching of a sheet. The governing partial differential equations are transformed into a nonlinear ordinary differential equation which is using appropriate boundary conditions for various physical parameters. The numerical solutions of the resulting nonlinear ODEs are found by using the efficient finite difference method (FDM). The effects of the slip parameter and the wall thickness parameter on the flow profile are presented. Moreover, the local skin friction is presented. Comparison of the obtained numerical results is made with previously published results in some special cases, and excellent agreement is noted. The results attained in this paper confirm the idea that FDM is a powerful mathematical tool and can be applied to a large class of linear and nonlinear problems arising in different fields of science and engineering.

The introduction of the quantum kinetic energy term via the Hamilton-Jacobi approach

Abstract: In this work, the quantum Hamilton-Jacobi equation, according to the Roncadelli and Schulman method, with some relevant modifications, and based on the de Broglie-Bohm approach to quantum mechanics, has been rewritten; also it has been extended to the relativistic regime. Then, based on the results, we have introduced a term as “quantum kinetic energy” which could provide a meaningful link between the Brownian theory and the nature of the wave function, once the existence of an additional real space-filling fluid has been accepted.

Analysis of F(R, T) gravity models through energy conditions

Abstract: This paper is devoted to study the energy conditions in the F(R, T) gravity for a FRW universe with perfect fluid, where R is the Ricci scalar and T is the torsion scalar. We construct the general energy conditions in this theory and reduce them in F(R) as well as F(T) theory of gravity. Further, we assume some viable models and investigate bounds on their constant parameters to satisfy the energy condition inequalities. We plot some of the cases using present-day values of the cosmological parameters and also check the results under cosmographic analysis. It is interesting to mention here that the model F(R, T) = μR + νT satisfies the energy conditions for different ranges of the parameters as well as represents the phantom behavior of the universe.

MHD three-dimensional flow of couple stress fluid with Newtonian heating

Abstract: Effects of Newtonian heating on the magnetohydrodynamic (MHD) three-dimensional flow past a stretching surface are analyzed. Mathematical formulation is completed using constitutive equations of couple stress fluid. A constant magnetic field normal to the surface is applied. Viscous dissipation and Joule heating effects are present. The transformation procedure reduces the involved partial differential equations into the ordinary differential equations. Series solutions of the resulting systems are constructed. The convergence of the obtained series solutions is seen through graphical results and tabular values. Numerical values of skin friction and the Nusselt number for different parameters are also tabulated and analyzed.

On CCC-predicted concentric low-variance circles in the CMB sky

Abstract: A new analysis of the CMB, using WMAP data, supports earlier indications of non-Gaussian features of concentric circles of low temperature variance. Conformal cyclic cosmology (CCC) predicts such features from supermassive black-hole encounters in an aeon preceding our Big Bang. The significance of individual low-variance circles in the true data has been disputed; yet a recent independent analysis has confirmed CCC's expectation that CMB circles have a non-Gaussian temperature distribution. Here we examine concentric sets of low-variance circular rings in the WMAP data, finding a highly non-isotropic distribution. A new “sky-twist” procedure, directly analysing WMAP data, without appeal to simulations, shows that the prevalence of these concentric sets depends on the rings being circular, rather than even slightly elliptical, numbers dropping off dramatically with increasing ellipticity. This is consistent with CCC's expectations; so also is the crucial fact that whereas some of the rings' radii are found to reach around 15° , none exceed 20° . The non-isotropic distribution of the concentric sets may be linked to previously known anomalous and non-Gaussian CMB features.

The thermal properties of a two-dimensional Dirac oscillator under an external magnetic field

Abstract: In the language of creation and annihilation operators, we study a relativistic spin- $$\tfrac{1} {2}$$ fermion subject to a Dirac oscillator (DO) coupling and a constant magnetic field in both commutative and non-commutative (NC) spaces All dynamical physical variables, in a two-dimensional complex formalism, are expressed in terms of the creation and annihilation operators via a z , $$\bar a_z$$ and a z , $$\bar a_z$$ in the commutative space, and d z , $$\bar d_z$$ and d z , $$\bar d_z$$ in the NC space The eigensolutions of our problem have been determinated, and the exact connection with both Jaynes-Cummings (JC) and anti-Jaynes-Cummings (AJC) models has been established In addition, we revealed the existence of the quantum phase transition in both commutative and NC spaces The thermal properties of the Dirac oscillator under a magnetic field, calculated from the partition function, have been investigated, and the effect of the non-commutative parameters on these properties has been tested

Spontaneous Lorentz violation in gauge theories

Abstract: Frohlich, Morchio and Strocchi long ago proved that the Lorentz invariance is spontaneously broken in QED because of infrared effects. We develop a simple model where the consequences of this breakdown can be explicitly and easily calculated. For this purpose, the superselected U(1) charge group of QED is extended to a superselected “Sky” group containing direction-dependent gauge transformations at infinity. It is the analog of the Spi group of gravity. As Lorentz transformations do not commute with Sky, they are spontaneously broken. These Abelian considerations and model are extended to non-Abelian gauge symmetries. Basic issues regarding the observability of twisted non-Abelian gauge symmetries and of the asymptotic ADM symmetries of quantum gravity are raised.

Reconstruction of f(G) gravity with the new agegraphic dark-energy model

Abstract: We consider the reconstruction scenario of the new agegraphic dark-energy model and f(G) theory of gravity where G represents the Gauss-Bonnet invariant in the flat FRW spacetime. In this context, we assume a solution of the scale factor in power law form and study the correspondence scenario. A new agegraphic f(G) model is constructed and discussed graphically for the evolution of the universe. Using this model, we investigate the different eras of the expanding universe and stability with the help of the equation-of-state (EoS) parameter and squared speed of sound, respectively. It is mentioned here that the reconstructed model represents the accelerated expansion of the universe with instability. Moreover, the statefinder trajectories are studied and we find out that the model is not capable of reaching the ΛCDM phase of the universe.

Topological 1-soliton solution of nonlinear Schrödinger equation with dual-power law nonlinearity in nonlinear optical fibers

Abstract: The nonlinear Schrodinger equation with dual-power law nonlinearity for describing the propagation of pulses through an optical fiber in an optical communication system is studied. The first integral method, which is based on the division theorem, is used for obtaining the exact 1-soliton solution of this equation. The exact 1-soliton solution is constructed through the established first integral.

Self-completeness and spontaneous dimensional reduction

Abstract: A viable quantum theory of gravity is one of the biggest challenges physicists are facing. We discuss the confluence of two highly expected features which might be instrumental in the quest of a finite and renormalizable quantum gravity —spontaneous dimensional reduction and self-completeness. The former suggests the spacetime background at the Planck scale may be effectively two-dimensional, while the latter implies a condition of maximal compression of matter by the formation of an event horizon for Planckian scattering. We generalize such a result to an arbitrary number of dimensions, and show that gravity in higher than four dimensions remains self-complete, but in lower dimensions it does not. In such a way we established an “exclusive disjunction” or “exclusive or” (XOR) between the occurrence of self-completeness and dimensional reduction, with the goal of actually reducing the unknowns for the scenario of the physics at the Planck scale. Potential phenomenological implications of this result are considered by studying the case of a two-dimensional dilaton gravity model resulting from dimensional reduction of the Einstein gravity.

Forty years of Galilean Electromagnetism (1973–2013)

Abstract: We review Galilean Electromagnetism since the 1973 seminal paper of Jean-Marc Levy-Leblond and Michel Le Bellac and we explain for the first time all the historical experiments of Rowland, Vasilescu Karpen, Roentgen, Eichenwald, Wilson, Wilson and Wilson, which were previously interpreted in a Special Relativistic framework by showing the uselessness of the latter for setups involving slow motions of a part of the apparatus. Galilean Electromagnetism is not an alternative to Special Relavity but is precisely its low-velocity limit in Classical Electromagnetism.

Soret and Dufour effects on the stagnation point flow of Jeffery fluid with convective boundary condition

Abstract: The influence of heat and mass transfer on the stagnation point flow near a stretched surface is explored. The problem formulation is completed using convective boundary conditions. Soret and Dufour effects are retained. The series solutions for velocity, temperature and concentration are constructed and discussed. Numerical values of skin friction coefficient, local Nusselt and Sherwood numbers are analyzed.

Kinetic theory of spatially homogeneous systems with long-range interactions: II. Historic and basic equations

Abstract: We provide a short historic of the early development of kinetic theory in plasma physics and synthesize the basic kinetic equations describing the evolution of systems with long-range interactions derived in Paper I. We describe the evolution of the system as a whole and the relaxation of a test particle in a bath of field particles at equilibrium or out of equilibrium. We write these equations for an arbitrary long-range potential of interaction in a space of dimension d . We discuss the scaling of the relaxation time with the number of particles for non-singular potentials. For always spatially homogeneous distributions, the relaxation time of the system as a whole scales like N in d > 1 and like N2 (presumably) or like eN (possibly) in d = 1 . For always spatially inhomogeneous distributions, the relaxation time of the system as a whole scales like N in any dimension of space. For 1D systems undergoing a dynamical phase transition from a homogeneous to an inhomogeneous phase, we expect a relaxation time of the form N δ with 1 < δ < 2 intermediate between the two previous cases. The relaxation time of a test particle in a bath always scales like N . We also discuss the kinetic theory of systems with long-range interactions submitted to an external stochastic potential. This paper gathers basic equations that are applied to specific systems in Paper III.

Wronskian representation for confluent supersymmetric transformation chains of arbitrary order

Abstract: We prove that iterations of confluent supersymmetric transformations (confluent SUSY chains) in quantum mechanics can be represented through Wronskian determinants. It is further shown that the latter Wronskian representation remains valid, if the SUSY chain is built from arbitrary combinations of confluent and non-confluent subchains. In addition, we obtain an integral representation of generalized eigenfunctions for quantum-mechanical Hamiltonians that proves useful for the application of confluent SUSY chains. Our results generalize former findings for second- and third-order chains.

Dynamics of charged radiating collapse in modified Gauss-Bonnet gravity

Abstract: This paper deals with the dynamics of a shearfree charged radiating collapse in the modified Gauss-Bonnet gravity. The field equations for shearfree spherical interior geometry of a charged dissipative star are formulated. To study the dynamical behavior of collapsing matter, we derive the dynamical as well as transport equations. We conclude that the gravitational force in the modified Gauss-Bonnet gravity is much stronger as compared to general relativity, which implies the increase in the rate of the collapse. Finally, we study the effect of the charge on the dynamics of the collapse.

Thermal radiation effects in squeezing flow of a Jeffery fluid

Abstract: The aim of this work is to analyze the thermal radiation effects in a time-dependent axisymmetric flow of a Jeffery fluid. The flow in a fluid is induced by the unsteady squeezing of two parallel disks. The related partial differential equations for the modeled problem are simplified and transformed into coupled ordinary differential equations by using appropriate transformations. The differential system is solved for the convergent series solution. Effects of the various physical parameters have been analyzed for suction and injection cases.

Solutions of the Klein-Gordon equation with the improved Rosen-Morse potential energy model

Abstract: We solve the Klein-Gordon equation with the improved Rosen-Morse empirical potential energy model. The bound-state energy equation has been obtained by using the supersymmetric shape invariance approach. The relativistic vibrational transition frequencies for the $3^{3}\Sigma_{g}^{+}$ state of the Cs2 molecule have been computed by using the improved Rosen-Morse potential model. The relativistic vibrational transition frequencies are in good agreement with the experimental RKR values and DPF values.

Generalized second law of thermodynamics in the emergent universe for some viable models of f(T) gravity

Abstract: The present work is motivated by the study of the paper K. Karami, A. Abdolmaleki, J. Cosmol. Astropart. Phys. 04, 007 (2012), where the generalized second law (GSL) of thermodynamics has been investigated for a flat FRW universe for three viable models of f(T) gravity. We have here considered a non-flat universe and, accordingly, studied the behaviors of the equation-of-state (EoS) parameter ω and of the deceleration parameter q. Subsequently, using the first law of thermodynamics, we derived the expressions for the time derivative of the total entropy of a universe enveloped by apparent horizon. In the next phase, with the choice of scale factor a(t) pertaining to an emergent universe, we have investigated the sign of the time derivatives of total entropy for the models of f(T) gravity considered.

Unsteady MHD three-dimensional flow with viscous dissipation and Joule heating

Abstract: This article addresses the viscous dissipation and Joule heating effects in unsteady magnetohydrodynamic (MHD) three-dimensional flow forced by an exponentially stretching surface. The momentum and thermal equations in the boundary layer regime are reduced into the ordinary differential equations using appropriate transformations. Computations for series solutions of velocity and temperature are first made and then analyzed with respect to influential parameters. Numerical values of skin friction coefficients and local Nusselt number are given and examined. The present results are also found to be in very good agreement with the existing aymptotic solutions.

Holographic reconstruction of f(G) gravity for scale factors pertaining to emergent, logamediate and intermediate scenarios

Abstract: In this paper, we reconstruct the holographic dark energy in the framework of the f (G) modified theory of gravity, where G is the Gauss-Bonnet invariant. In this context, we choose the infrared cut-off as the Granda-Oliveros cut-off, which is proportional to the Hubble parameter H and its first derivative with respect to the cosmic time t . We reconstruct the f (G) model with the inclusion of HDE and the three well-known forms of the scale factor a(t) , i.e. the emergent, the logamediate and the intermediate scale factors. The reconstructed model as well as equation of state parameter are discussed numerically with the help of graphical representations to explore the accelerated expansion of the universe. Moreover, the stability of the models incorporating all the scale factors is checked through squared speed of sound v s 2.

Anandan quantum phase and quantum holonomies induced by the effects of the Lorentz symmetry violation background in the CPT-even gauge sector of the Standard Model Extension

Abstract: We study the rise of geometric quantum phases corresponding to the analogues of the Anandan quantum phase (J. Anandan, Phys. Lett. A 138, 347 (1989)) based on possible scenarios of the Lorentz symmetry violation background in the CPT-even gauge sector of the Standard Model Extension. We also show that we can obtain quantum holonomies associated with the analogues of the Anandan quantum phase, and discuss a possible analogy with the holonomic quantum computation (P. Zanardi, M. Rasetti, Phys. Lett. A 264, 94 (1999)).

Exact multisoliton solutions of nonlinear Klein-Gordon equation in 1 + 2 dimensions

Abstract: This paper studies the nonlinear generalized Klein-Gordon equation in 1 + 2 dimensions. Exact multisoliton solution of this equation is obtained for the case of quadratic-law nonlinearity by the formal linearization method. Subsequently, exact travelling wave solutions of the generalized forms of Klein-Gordon equations in 1 + 2 dimensions are established by the modification of the truncated expansion method.

An approximate approach to the nonlinear DGLAP evaluation equation

Abstract: We determined the effects of the first nonlinear corrections to the gluon distribution using the solution of the QCD nonlinear Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (NLDGLAP) evolution equation at small x. By using a Laplace-transform technique, the behavior of the gluon distribution is obtained by solving the Gribov, Levin, Ryskin, Mueller and Qiu (GLR-MQ) evolution equation with the nonlinear shadowing term incorporated. We show that the strong rise that is corresponding to the linear QCD evolution equations at small x can be tamed by screening effects. Consequently, the nonlinear effects for the gluon distributions are calculated and compared with the results for the integrated gluon density from the Balitsky-Kovchegov (BK) equation. The resulting analytic expression allows us to predict the shadowing correction to the logarithmic derivative F 2(x, Q 2) with respect to ln Q 2 and to compare the results with H1 data and a QCD analysis fit.

Combined thermal stratified and thermal radiation effects in mixed-convection flow of a thixotropic fluid

Abstract: This article addresses the mixed-convectionflow of a thixotropic fluid over a linearly stretching surface. Thermal stratified effects are taken into account in the presence of thermal radiation. Governing partial differential equations are first reduced into the ordinary differential equations and then solved for the homotopic solutions. Graphs to the obtained expressions are sketched for different parameters. Numerical values of skin-friction coefficient and local Nusselt number are computed with and without thermal stratified effects in viscous and non-Newtonian fluids.

Infinite face-centered-cubic network of identical resistors: Application to lattice Green's function

Abstract: The equivalent resistance between the origin and any other lattice site, in an infinite face-centered-cubic network consisting of identical resistors, has been expressed rationally in terms of the known value $ f_o(3;0,0,0)$ and $ \pi$ . The asymptotic behavior is investigated, and some calculated values for the equivalent resistance are presented.

The EEE experiment project: status and first physics results

Abstract: The Extreme Energy Events Project is an experiment for the detection of Extensive Air Showers which exploits the Multigap Resistive Plate Chamber technology. At the moment 40 EEE muon telescopes, distributed all over the Italian territory, are taking data, allowing the relative analysis to produce the first interesting results, which are reported here. Moreover, this Project has a strong added value thanks to its effectiveness in terms of scientific communication, which derives from the peculiar way it was planned and carried on.

Neutron transmission and capture cross section measurements for 241Am at the GELINA facility

Abstract: Resonance parameters for neutron-induced reactions on 241Am below 110 eV have been determined. The parameters result from a resonance shape analysis of transmission and capture data measured at the time-of-flight facility GELINA, with the accelerator operating at a 50 Hz repetition rate. The transmission experiments were carried out at a 25 m station using a Li glass scintillator. The capture experiments were performed at a 12.5 m station by applying the total energy detection principle in combination with the pulse height weighting technique using a pair of C6D6 detectors. The normalization of the capture data was determined by a combined least squares adjustment of the transmission and capture data. From the adjusted resonance parameters a capture cross section of 749 ± 35 b for a neutron energy of 0.0253 eV and an average radiation width of 〈Γ γ 〉 = 42.0 meV for s-wave resonances were obtained. A missing-level analysis for s-wave neutron resonances within the statistical model results in compatible values with previous estimates. The neutron widths obtained in this work are approximately 22% larger compared to other experimental data and evaluated data libraries. Also the thermal capture cross section is larger than most of the recommended values. However, the resonance parameter file presented in this work is consistent with results of both integral experiments and of the experimentally determined resonance integrals.

Heavy quark perturbative QCD fragmentation functions in the presence of hadron mass

Abstract: The dominant mechanism to produce hadronic bound states with large transverse momentum is fragmentation, that is the splitting of a high-energy parton into a hadronic state and other partons. We review the present schemes to calculate the heavy quark fragmentation functions (FFs) and derive an exact analytical expression of FF which includes most of the kinematical and dynamical properties of the process. Using the perturbative QCD, we calculate the FF for c-quark to split into S-wave D+ meson to leading order in the QCD coupling constant. Our result is compared with the current well-known phenomenological models which are obtained through a global fit to e+e− data from SLAC SLC and CERN LEP1 and we also compare the FF with experimental data form BELLE and CLEO. Specifically, we study the effect of outgoing meson mass on the pQCD FF. Meson masses are responsible for the low-z threshold, where z is the scaled energy variable.