Showing papers in "European Physical Journal Plus in 2012"

Noninertial effects on the Dirac oscillator in a topological defect spacetime

Abstract: In this paper, we study the influence of noninertial effects on the Dirac oscillator in the cosmic string spacetime background. We discuss the behaviour of the oscillator frequency in a noninertial system that allows us to obtain relativistic bound state solutions. We also discuss the influence of the topology of the cosmic string spacetime on the relativistic energy levels, and obtain the Dirac spinors for positive-energy solutions. Furthermore, by taking the nonrelativistic limit of the energy levels, we compare the nonrelativistic energy levels to the confinement of a spin-half particle to quantum dot described by the Tan-Inkson model for a quantum dot (W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)), and a hard-wall confining potential (E. Tsitsishvili et al., Phys. Rev. B 70, 115316 (2004)).

Testing General Relativity and gravitational physics using the LARES satellite

Abstract: The discovery of the accelerating expansion of the Universe, thought to be driven by a mysterious form of “dark energy” constituting most of the Universe, has further revived the interest in testing Einstein’s theory of General Relativity. At the very foundation of Einstein’s theory is the geodesic motion of a small, structureless test-particle. Depending on the physical context, a star, planet or satellite can behave very nearly like a test-particle, so geodesic motion is used to calculate the advance of the perihelion of a planet’s orbit, the dynamics of a binary pulsar system and of an Earth-orbiting satellite. Verifying geodesic motion is then a test of paramount importance to General Relativity and other theories of fundamental physics. On the basis of the first few months of observations of the recently launched satellite LARES, its orbit shows the best agreement of any satellite with the test-particle motion predicted by General Relativity. That is, after modelling its known non-gravitational perturbations, the LARES orbit shows the smallest deviations from geodesic motion of any artificial satellite: its residual mean acceleration away from geodesic motion is less than $\ensuremath 0.5\times10^{-12}$ m/s^2. LARES-type satellites can thus be used for accurate measurements and for tests of gravitational and fundamental physics. Already with only a few months of observation, LARES provides smaller scatter in the determination of several low-degree geopotential coefficients (Earth gravitational deviations from sphericity) than available from observations of any other satellite or combination of satellites.

Relativistic symmetries of Dirac equation and the Tietz potential

Abstract: Relativistic symmetries of the Dirac equation, namely the spin and pseudospin symmetries, are investigated under the Tietz potential for the scalar and vector interactions beside a Coulomb tensor term. The analytical approach of supersymmetry quantum mechanics is applied to the problem and the problem is discussed in a quite detailed manner.

Looking for magnetic monopoles at LHC with diphoton events

Abstract: Magnetic monopoles have been a subject of interest since Dirac established the relation between the existence of monopoles and charge quantization. The intense experimental search carried thus far has not met with success. The Large Hadron Collider is reaching energies never achieved before allowing the search for exotic particles in the TeV mass range. In a continuing effort to discover these rare particles we propose here other ways to detect them. We study the observability of monopoles and monopolium, a monopole-antimonopole bound state, at the Large Hadron Collider in the γγ channel for monopole masses in the range 500–1000 GeV. We conclude that LHC is an ideal machine to discover monopoles with masses below 1TeV at present running energies and with 5 fb−1 of integrated luminosity.

Pippi — Painless parsing, post-processing and plotting of posterior and likelihood samples

Abstract: Interpreting samples from likelihood or posterior probability density functions is rarely as straightforward as it seems it should be. Producing publication-quality graphics of these distributions is often similarly painful. In this short note I describe pippi, a simple, publicly available package for parsing and post-processing such samples, as well as generating high-quality PDF graphics of the results. Pippi is easily and extensively configurable and customisable, both in its options for parsing and post-processing samples, and in the visual aspects of the figures it produces. I illustrate some of these using an existing supersymmetric global fit, performed in the context of a gamma-ray search for dark matter. Pippi can be downloaded and followed at http://github.com/patscott/pippi.

On the black hole’s thermodynamics and the entropic origin of gravity

Abstract: The effects of gravity on the Schwarzschild’s black-hole behavior is described on using the thermodynamic equations of state for contractile materials. Its entropy and temperature, obtained by using classical principles, reproduce the results derived from quantum field theories and statistical mechanics. The given results show that, by using the gravitational dynamics to reproduce the thermodynamic equation TdS/dx = F gravity , there is no way to establish the entropic origin of gravity, because the results can be seen the other way around.

On the influence of a Coulomb-like potential induced by the Lorentz symmetry breaking effects on the harmonic oscillator

Abstract: In this work, we obtain bound states for a nonrelativistic spin-half neutral particle under the influence of a Coulomb-like potential induced by the Lorentz symmetry breaking effects. We present a new possible scenario of studying the Lorentz symmetry breaking effects on a nonrelativistic quantum system defined by a fixed space-like vector field parallel to the radial direction interacting with a uniform magnetic field along the z -axis. Furthermore, we also discuss the influence of a Coulomb-like potential induced by Lorentz symmetry violation effects on the two-dimensional harmonic oscillator.

Plotting the differences between data and expectation

Abstract: This article proposes a way to improve the presentation of histograms where data are compared to expectation. Sometimes, it is difficult to judge by eye whether the difference between the bin content and the theoretical expectation (provided by either a fitting function or another histogram) is just due to statistical fluctuations. More importantly, there could be statistically significant deviations which are completely invisible in the plot. We propose to add a small inset at the bottom of the plot, in which the statistical significance of the deviation observed in each bin is shown. Even though the numerical routines which we developed have only illustration purposes, it comes out that they are based on formulae which could be used to perform statistical inference in a proper way.

Oscillator strengths based on the Möbius square potential under Schrödinger equation

Abstract: By applying the NU method and an approximation to the centrifugal term, we have solved the Schrodinger equation in D-dimensions for the Mobius square potential which in some particular cases gives the Morse and Hulthen potentials. The eigenfunctions as well as the energy eigenvalues are obtained and some expectation values are reported. The important parameter of oscillator strength is obtained and discussed in terms of various parameters of the system.

Minimizing Higgs potentials via numerical polynomial homotopy continuation

Abstract: The study of models with extended Higgs sectors requires to minimize the corresponding Higgs potentials, which is in general very difficult. Here, we apply a recently developed method, called numerical polynomial homotopy continuation (NPHC), which guarantees to find all the stationary points of the Higgs potentials with polynomial-like non-linearity. The detection of all stationary points reveals the structure of the potential with maxima, metastable minima, saddle points besides the global minimum. We apply the NPHC method to the most general Higgs potential having two complex Higgs-boson doublets and up to five real Higgs-boson singlets. Moreover the method is applicable to even more involved potentials. Hence the NPHC method allows to go far beyond the limits of the Grobner basis approach.

The Sudakov Veto Algorithm Reloaded

Abstract: We perform a careful analysis of the main Monte Carlo algorithm used in parton shower simulations, the Sudakov veto algorithm. We prove a general version of the algorithm, directly including the dependence on the infrared cutoff. Taking this as a starting point, we then consider non-positive definite splitting kernels, as encountered when dealing with sub-leading colour correlations or splitting kernels beyond leading order. New algorithms suited for these situations are developed.

Schwarzschild's singularity is semi-regularizable

Abstract: It is shown that the Schwarzschild spacetime can be extended so that the metric becomes analytic at the singularity. The singularity continues to exist, but it is made degenerate and smooth, and the infinities are removed by an appropriate choice of coordinates. A family of analytic extensions is found, and one of these extensions is semi-regular. A degenerate singularity does not destroy the topology, and when it is semi-regular, it allows the field equations to be rewritten in a form which avoids the infinities, as it was shown elsewhere. In the new coordinates, the Schwarzschild solution extends beyond the singularity. This suggests a possibility that the information is not destroyed in the singularity, and can be restored after the evaporation.

Analytical solution of N-dimensional Klein-Gordon and Dirac equations with Rosen-Morse potential

Abstract: The solutions of the N-dimensional Klein-Gordon and Dirac wave equations with equal scalar and vector Rosen-Morse potentials are studied. The energy equations and the radial wave functions are derived using the Nikiforov-Uvarov method. The low-dimensional (N = 3 s-wave limits and the variation of the bound-state energies with the dimension and the angular momentum are discussed.

String cosmological models from early deceleration to current acceleration phase with varying G and $ \Lambda$

Abstract: Thepresent study deals with spatially homogeneous and anisotropic Bianchi-I cosmological models representing massive strings with variable G and decaying vacuum energy density \( \Lambda\) . The energy-momentum tensor, as formulated by Letelier (Phys. Rev. D 20, 1294 (1979); Phys. Rev. D 28, 2414 (1983)), has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor and barotropic EoS. The Einstein field equations have been solved by considering the time-dependent deceleration parameter which yields a scale factor \( a(t) = (\sinh(\alpha t))^{\frac{1}{n}}\) , where n is a positive constant. For n > 1 , this generates a transition of the Universe from the early decelerating phase to the recent accelerating phase and the transition redshift zt has been calculated. The study reveals that massive strings dominate the early Universe evolving with deceleration and in the later phase they disappear, which is in good agreement with current astronomical observations. The cosmological constant \( \Lambda\) is found to be a positive decreasing function of time which is corroborated by results from recent Supernovae Ia observations. The physical and geometric properties of the models have been also discussed in detail.

Re-Evaluation of Neutrino Mixing Pattern According to Latest T2K result

Abstract: We re-evaluate neutrino mixing patterns according to the latest T2K result for a larger mixing angle θ 13, and find that the PMNS mixing matrix has larger deviations from bimaximal (BM) and tribimaximal (TB) mixing patterns than previously expected. We also find that several schemes connecting PMNS and CKM mixing matrices can accommodate the latest T2K result nicely. As necessary updates to former works, we make new triminimal expansions of PMNS mixing matrix based on BM and TB mixing patterns. We also propose a new mixing pattern with a self-complementary relation between the mixing angles θ 12 + θ 13 ⋍ 45°, and find such a new mixing pattern in leading order can provide a rather good description of the data.

On small proofs of the Bell-Kochen-Specker theorem for two, three and four qubits

Abstract: The Bell-Kochen-Specker (BKS) theorem rules out realistic non-contextual theories by resorting to impossible assignments of rays among a selected set of maximal orthogonal bases. We investigate the geometrical structure of small v-l BKS proofs involving v real rays and l 2n-dimensional bases of n-qubits (1 < n 5). Specifically, we look at the parity proof 18-9 with two qubits (A. Cabello, 1996), the parity proof 36-11 with three qubits (M. Kernaghan, A. Peres, 1995) and a newly discovered non-parity proof 80-21 with four qubits (that improves work of P.K. Aravind’s group in 2008). The rays in question arise as real eigenstates shared by some maximal commuting sets (bases) of operators in the n-qubit Pauli group. One finds characteristic signatures of the distances between the bases, which carry various symmetries in their graphs.

Thermodynamics of phantom Reissner-Nordstrom-AdS black hole

Abstract: We obtain a new solution of the Einstein-anti-Maxwell theory with cosmological constant, called anti-Reissner-Nordstrom-(A)de Sitter (anti-RN-(A)dS) solution The basic properties of this solution is reviewed Its thermodynamics is consistently established, with the extreme cases and phase transitions, where the analysis is performed through two methods, the usual one and that of Geometrothermodynamics The Geometrothermodynamics analysis does not provide a result in agreement with the usual method or by the specific heat We establish local and global thermodynamic stabilities of anti-RN-AdS solution through the specific heat and the canonical and grand-canonical ensembles

Measurement of the cosmic ray energy spectrum using hybrid events of the Pierre Auger Observatory

Abstract: The energy spectrum of ultra-high energy cosmic rays above 10(18)eV is measured using the hybrid events collected by the Pierre Auger Observatory between November 2005 and September 2010. The large exposure of the Observatory allows the measurement of the main features of the energy spectrum with high statistics. Full Monte Carlo simulations of the extensive air showers (based on the CORSIKA code) and of the hybrid detector response are adopted here as an independent cross check of the standard analysis (Phys. Lett. B 685, 239 (2010)). The dependence on mass composition and other systematic uncertainties are discussed in detail and, in the full Monte Carlo approach, a region of confidence for flux measurements is defined when all the uncertainties are taken into account. An update is also reported of the energy spectrum obtained by combining the hybrid spectrum and that measured using the surface detector array.

A suite of user-friendly global climate models: Hysteresis experiments

Abstract: A hierarchy of global spectral circulation models is introduced ranging from the shallow-water system via the primitive-equation dynamical core of the atmosphere to the Planet Simulator as a Global Climate Model (GCM) of Intermediate Complexity (MIC) which can be used to run climate and paleo-climate simulations for time scales up to ten thousand years or more in an acceptable real time. The priorities in development are set to speed, easy handling and portability with a modular structure suitable for problem-dependent configuration. Adaptions exist for the planetary atmospheres of Mars and of Saturn’s moon Titan and are being extended. Common coupling interfaces enable the addition of ocean, ice, vegetation models and more. An interactive mode with a Model Starter and a Graphical User Interface (GUI) is available to select a configuration from the available model suite, to set its parameters and inspect atmospheric fields while changing the models’ parameters on the fly. This is especially useful for teaching, debugging and tuning of parameterizations. An updated overview of the model suite’s features is presented based on the Earth-like climate model Planet Simulator with mixed-layer ocean introducing static and memory hysteresis in terms of a parameter sweep of the solar constant and CO2 concentrations. The static hysteresis experiment demonstrates that the solar constant varying by 20% reveals warm and snowball Earth climate regimes depending on the history of the system. This hysteresis subjected to a thermodynamic analysis shows the following features: i) Both climate regimes are characterized by global mean surface temperature and entropy growing with increasing solar constant. ii) The climate system’s efficiency decreases (increases) with increasing solar constant in present-day warm (snowball) climate conditions. iii) Climate transitions near bifurcation points are characterized by high efficiency associated with the system’s large distance from the stable regime. Memory hysteresis evolves when changing the direct atmospheric radiative forcing which, associated with a well-mixed CO2 concentration, modifies the planetary thermodynamic state, and hence the surface temperature. The hysteresis effected by different CO2 change rates is analysed: i) The response is due to infrared cooling (for constant temperature lapse-rate) which, in turn, is related to the surface temperature through the Stefan-Boltzmann law in a ratio proportional to the new infrared opacity. Subsequent indirect effects, that are water-vapour-greenhouse and ice-albedo feedbacks, enhance the response. ii) Different rates of CO2 variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO2 concentration. iii) Far from the bifurcation points, the model’s climate depends on the history of the radiative forcing thus displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model determined by the mixed-layer depth of the ocean. Results are supported by a zero-dimensional energy balance model.

Kinetic theory of spatially homogeneous systems with long-range interactions: I. General results

Abstract: We review and complete the existing literature on the kinetic theory of spatially homogeneous systems with long-range interactions taking collective effects into account. The evolution of the system as a whole is described by the Lenard-Balescu equation which is valid in a weak coupling approximation. When collective effects are neglected it reduces to the Landau equation and when collisions (correlations) are neglected it reduces to the Vlasov equation. The relaxation of a test particle in a bath is described by a Fokker-Planck equation involving a diffusion term and a friction term. For a thermal bath, the diffusion and friction coefficients are connected by an Einstein relation. General expressions of the diffusion and friction coefficients are given, depending on the potential of interaction and on the dimension of space. We also discuss the scaling with $N$ (number of particles) or with $\Lambda$ (plasma parameter) of the relaxation time towards statistical equilibrium. Finally, we consider the effect of an external stochastic forcing on the evolution of the system and compute the corresponding term in the kinetic equation.

Using Weyl symmetry to make graphene a real lab for fundamental physics

Abstract: I review recent work on the applications of the Weyl symmetry to the electronic properties of graphene, by enlarging and deepening the discussion of certain aspects, and by pointing the wayto the steps necessary to make graphene a testing ground of fundamental ideas.

Entropic force approach to noncommutative Schwarzschild black holes signals a failure of current physical ideas

Abstract: Recently, a new perspective of gravitational-thermodynamic duality as an entropic force arising from alterations in the information associated with the positions of material bodies is found. In this paper, we generalize some features of this model in the presence of noncommutative Schwarzschild black hole by applying the method of coordinate coherent states describing smeared structures. We employ two different distributions: a) Gaussian and b) Lorentzian. Both mass distributions provide the similar quantitative aspects for the entropic force. Our study show the entropic force on the smallest fundamental unit of the holographic screen with radius r0 is zero. As a result, black-hole remnants are unconditionally inert and gravitational interactions do not exist therein. So, a distinction between gravitational and inertial mass in the size of black-hole remnant is observed, i.e. the failure of the principle of equivalence. In addition, if one considers the screen radius to be less than the radius of the smallest holographic surface at the Planckian regime, then one encounters some unusual dynamical features leading to gravitational repulsive force and negative energy. On the other hand, the significant distinction between the two distributions is perceived to occur around r0, and that is worth of mentioning: at this regime either our analysis is not the proper one, or nonextensive statistics should be applied.

Exact solution Dirac equation for an energy-dependent potential

Abstract: We study Dirac equation for an energy-dependent potential in the presence of spin and pseudospin symmetries with arbitrary spin-orbit quantum number \( \kappa\) . We calculate the corresponding eigenfunctions and eigenvalues of this system by comparing with analytically solvable energy-dependent potentials. Some numerical results are given in the presence and absence of tensor interaction.

Magnetized dark energy and the late time acceleration

Abstract: In the present work we have searched the existence of the late time acceleration of the Universe. The matter source that is responsible for the late time acceleration of the Universe consists of cosmic fluid with the equation of state parameter $\ensuremath \omega = p/\rho$ and uniform magnetic field of energy density $\ensuremath \rho_{B}$ . The study is done here under the framework of spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi-I cosmological model in the presence of magnetized dark energy. To get the deterministic model of the Universe, we assume that the shear scalar ( $ \sigma$ ) in the model is proportional to expansion scalar ( $ \theta$ ) . This condition leads to $\ensuremath A=B^{n}$ , where A and B are metric functions and n is a positive constant giving the proportionality condition between shear and expansion scalar. It has been found that the isotropic distribution of magnetized dark energy leads to the present accelerated expansion of the Universe and the derived model is in good agreement with the recent astrophysical observations. The physical behavior of the Universe has been discussed in details.

Dynamics of a biological system with time-delayed noise

Abstract: This work studies the dynamics of a biological system with a time-delayed random excitation. The model used is a multi-limit-cycle variation of the Van der Pol oscillator introduced to analyze enzymatic substrate reactions in brain waves. We found birhythmicity in the system and observed that the two frequencies are strongly influenced by the nonlinear coefficients. In the presence of a random excitation, such as a Gaussian white noise, the stability of the attractor is measured by calculating Kramer’s escape time. The activation energy is also estimated. Taking into account the time delay on the Gaussian white noise, we showed that the problem of the traditional Kramer escape time can be extended to analyze a bistable system under the influence of a noise made up of a superposition of a Gaussian white noise and its replicas delayed of time τ. The escape times for the intervals 0 < t < τ and τ < t < 2τ are calculated analytically.

First experimental detection of antiproton in-flight annihilation on nuclei at ∼ 130 keV

Abstract: The existing data of antinucleon-nucleon and antinucleon-nuclei annihilation cross-sections are confined to energies above about 1MeV. Experimental limitations have prevented till now the lower energies data to be achieved in spite of the interest they represent for theoretical models. One of the unresolved question concerns the antiproton annihilation cross-section measured at LEAR on light nuclei in the MeV region, which show a saturation with the mass number of the target nucleus against any naive expectation. With regard to fundamental cosmology, the knowledge of the annihilation cross-sections at energies below 1MeV can contribute to understand the matter-antimatter asymmetry in the Universe. We present here the experimental demonstration of the feasibility of the measurement of antiproton-nuclei annihilation cross-sections in the 100 keV region.

The Baksan Neutrino Observatory

Abstract: An overall view of the history of the Baksan Neutrino Observatory INR RAS creation is presented. Ground-based and underground facilities used to study cosmic rays, rare nuclear reactions and decays, register solar neutrinos, observe various geophysical phenomena are described. Some main results obtained with these facilities are given.

The SNOLAB deep underground facility

Abstract: The rigorous radiation background constraints imposed by several studies in particle and astro-particle physics, such as Galactic dark-matter searches, man-made, terrestrial, solar and supernova neutrino studies and 0νββ-decay studies, require deep underground science facilities to afford shielding from penetrating cosmic rays and their secondary by-products. New threads of research focused on deep sub-surface biology, chemistry, geology and engineering have also been developing rapidly at several sites, benefitting from the significant investment in underground access and infrastructure developed. This paper summarises the developments at the SNOLAB deep underground facility in Canada, following the significant expansion of the availablespace within this facility.

Simulations of planar channeling of relativistic nuclei in a bent crystal

Abstract: The motion of relativistic nuclei through an oriented bent crystal was considered on the basis of a developed computer code. To get the angular distributions of projectiles behind the crystals and to estimate the influence of multiple scattering on beam deflection, a detailed study of the beam dynamics due to the processes of channeling, dechanneling and quasichanneling of the particles is presented. The analysis of the beam redistribution in a crystal was performed simulating the main features of the scattering of relativistic Pb ions and protons in the field of bent crystal planes. The comparison of simulated data with experimental ones has been also carried out.

A new approach to Lorentz invariance in electromagnetism with hyperbolic octonions

Abstract: In this study, after introducing the hyperbolic octonionic (counteroctonion) algebra and its properties, Maxwell’s equations with magnetic monopole and currents, Lorenz conditions for the electric, magnetic fields and Lorentz invariance are presented in detail with the most acknowledged forms using vectors. In a subsequent step, the differential operator and Laplacian, the hyperbolic octonionic Lorentz invariance of Maxwell’s equations with monopole and relevant field equations, which are newly described, and the components of the wave equation are obtained in a compact, useful, simple and elegant form in higher dimensions. This approach demonstrates that the hyperbolic octonionic representations for the Lorentz invariance of Maxwell’s equations with magnetic monopole can also contribute to field theories. Maxwell’s equations with sources are provided in Gauss units. As a result, the terms of Lorentz invariance for electromagnetism with the newly described field equations, and the wave equation are clearly attained in the hyperbolic octonionic algebra.