Quark Condensate in the Deuteron

We study the changes produced by the deuteron on the QCD quark condensate by means the Feynman-Hellmann theorem and find that the pion mass dependence of the pion-nucleon coupling could play an important role. We also discuss the relation between the many body effect of the condensate and the meson exchange currents, as seen by photons and pions. For pion probes, the many-body term in the physical amplitude differs significantly from that of soft pions, the one linked to the condensate. Thus no information about the many-body term of the condensate can be extracted from the pion-deuteron scattering length. On the other hand, in the Compton amplitude, the relationship with the condensate is a more direct one.Comment: to appear in Physics Review C (19 pages, 3 figures

GUI Matlab para o cálculo de funções de Bessel usando frações continuadas

[EN] Higher order Bessel functions are prevalent in physics and engineering and there exist different methods to evaluate them quickly and efficiently. Two of these methods are Miller's algorithm and the continued fractions algorithm. Miller's algorithm uses arbitrary starting values and normalization constants to evaluate Bessel functions. The continued fractions algorithm directly computes each value, keeping the error as small as possible. Both methods respect the stability of the Bessel function recurrence relations. Here we outline both methods and explain why the continued fractions algorithm is more efficient. The goal of this paper is both (1) to introduce the continued fractions algorithm to physics and engineering students and (2) to present a MATLAB GUI (Graphic User Interface) where this method has been used for computing the Semi-integer Bessel Functions and their zeros.[PT] Funções de Bessel de ordem mais alta são recorrentes em física e nas engenharias, sendo que há diferentes métodos para calculá-las de maneira rápida e eficiente. Dois destes métodos são o algoritmo de Miller e o algoritmo de frações continuadas. O primeiro faz uso de valores iniciais e constantes de normalização arbitrários, enquanto o segundo o faz calculando cada valor diretamente, minimizando tanto quanto possível o erro. Ambos respeitam a estabilidade das relações de recorrência das funções de Bessel. Neste trabalho descrevemos ambos os métodos e explicamos a razão pela qual o algoritmo das frações continuadas é mais eficiente. O objetivo do artigo é (1) introduzir o algoritmo de frações continuadas para estudantes de física e das engenharias e (2) apresentar um GUI (Graphic User Interface) em Matlab no qual este método foi utilizado para calcular funções de Bessel semi-inteiras e seus zeros.The authors wish to thank the financial support received from the Universidad Politécnica de Valencia under grant PAID-06-09-2734, from the Ministerio de Ciencia e Innovación through grant ENE2008-00599 and specially from the Generalitat Valenciana under grant reference 3012/2009.Hernandez Vargas, E.; Commeford, K.; Pérez Quiles, MJ. (2011). MATLAB GUI for computing Bessel functions using continued fractions algorithm. Revista Brasileira de Ensino de Física. 33(1):1303-1311. https://doi.org/10.1590/S1806-11172011000100003S13031311331Giladi, E. (2007). Asymptotically derived boundary elements for the Helmholtz equation in high frequencies. Journal of Computational and Applied Mathematics, 198(1), 52-74. doi:10.1016/j.cam.2005.11.024Havemann, S., & Baran, A. J. (2004). Calculation of the phase matrix elements of elongated hexagonal ice columns using the T-matrix method. Journal of Quantitative Spectroscopy and Radiative Transfer, 89(1-4), 87-96. doi:10.1016/j.jqsrt.2004.05.014Segura, J., Fernández de Córdoba, P., & Ratis, Y. L. (1997). A code to evaluate modified bessel functions based on thecontinued fraction method. Computer Physics Communications, 105(2-3), 263-272. doi:10.1016/s0010-4655(97)00069-6Bastardo, J. L., Abraham Ibrahim, S., Fernández de Córdoba, P., Urchueguía Schölzel, J. F., & Ratis, Y. L. (2005). Evaluation of Fresnel integrals based on the continued fractions method. Applied Mathematics Letters, 18(1), 23-28. doi:10.1016/j.aml.2003.12.009Barnett, A. R., Feng, D. H., Steed, J. W., & Goldfarb, L. J. B. (1974). Coulomb wave functions for all real η and ϱ. Computer Physics Communications, 8(5), 377-395. doi:10.1016/0010-4655(74)90013-

Density functional study of Aun_n (n=2-20) clusters: lowest-energy structures and electronic properties

We have investigated the lowest-energy structures and electronic properties of the Au$_n$(n=2-20) clusters based on density functional theory (DFT) with local density approximation. The small Au$_n$ clusters adopt planar structures up to n=6. Tabular cage structures are preferred in the range of n=10-14 and a structural transition from tabular cage-like structure to compact near-spherical structure is found around n=15. The most stable configurations obtained for Au$_{13}$ and Au$_{19}$ clusters are amorphous instead of icosahedral or fcc-like, while the electronic density of states sensitively depend on the cluster geometry. Dramatic odd-even alternative behaviors are obtained in the relative stability, HOMO-LUMO gaps and ionization potentials of gold clusters. The size evolution of electronic properties is discussed and the theoretical ionization potentials of Au$_n$ clusters compare well with experiments.Comment: 6 pages, 7 figure

Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources

We introduce a method to quantify the quality-of-fit between data and observables depending on the large scale Galactic magnetic field. We combine WMAP5 polarized synchrotron data and Rotation Measures of extragalactic sources in a joint analysis to obtain best fit parameters and confidence levels for GMF models common in the literature. None of the existing models provide a good fit in both the disk and halo regions, and in many instances best-fit parameters are quite different than the original values. We note that probing a very large parameter space is necessary to avoid false likelihood maxima. The thermal and relativistic electron densities are critical for determining the GMF from the observables but they are not well constrained. We show that some characteristics of the electron densities can already be constrained using our method and with future data it may be possible to carry out a self-consistent analysis in which models of the GMF and electron densities are simultaneously optimized.Comment: 27 pages, 13 figures. Accepted for publication in JCAP; arXiv version updated to include minor revision

Generating a checking sequence with a minimum number of reset transitions

Given a finite state machine M, a checking sequence is an input sequence that is guaranteed to lead to a failure if the implementation under test is faulty and has no more states than M. There has been much interest in the automated generation of a short checking sequence from a finite state machine. However, such sequences can contain reset transitions whose use can adversely affect both the cost of applying the checking sequence and the effectiveness of the checking sequence. Thus, we sometimes want a checking sequence with a minimum number of reset transitions rather than a shortest checking sequence. This paper describes a new algorithm for generating a checking sequence, based on a distinguishing sequence, that minimises the number of reset transitions used.This work was supported in part by Leverhulme Trust grant number F/00275/D, Testing State Based Systems, Natural Sciences and Engineering Research Council (NSERC) of Canada grant number RGPIN 976, and Engineering and Physical Sciences Research Council grant number GR/R43150, Formal Methods and Testing (FORTEST)

A Compact Beam Stop for a Rare Kaon Decay Experiment

We describe the development and testing of a novel beam stop for use in a rare kaon decay experiment at the Brookhaven AGS. The beam stop is located inside a dipole spectrometer magnet in close proximity to straw drift chambers and intercepts a high-intensity neutral hadron beam. The design process, involving both Monte Carlo simulations and beam tests of alternative beam-stop shielding arrangements, had the goal of minimizing the leakage of particles from the beam stop and the resulting hit rates in detectors, while preserving maximum acceptance for events of interest. The beam tests consisted of measurements of rates in drift chambers, scintilation counter hodoscopes, a gas threshold Cherenkov counter, and a lead glass array. Measurements were also made with a set of specialized detectors which were sensitive to low-energy neutrons, photons, and charged particles. Comparisons are made between these measurements and a detailed Monte Carlo simulation.Comment: 39 pages, 14 figures, submitted to Nuclear Instruments and Method

Charged and Pseudoscalar Higgs production at a Muon Collider

We consider single charged Higgs ($H^{\pm}$) and pseudoscalar Higgs ($A^0$) production in association with a gauge boson at $\mu^+\mu^-$ colliders. We find that the tree-level t-channel and s-channel contributions to $\mu^+\mu^-\to H^{\pm}W^{\mp}, A^0Z$ are enhanced for large values of $\tan\beta$, allowing sizeable cross-sections whose analogies at $e^+e^-$ colliders would be very small. These processes provide attractive new ways of producing such particles at $\mu^+\mu^-$ colliders and are superior to the conventional methods in regions of parameter space.Comment: 11 pages Latex, 5 figures, formulae added in sections 2.2 and 2.3, extra discussion in section 2.3, references adde

Exact formulae for Higgs production through e gamma --> e H in the non-linear R_\xi gauge

We study the production of the SM Higgs boson (H^0) at future e gamma colliders, through the reaction e gamma --> e H^0. The amplitude is evaluated using the non-linear R_\xi gauge, which greatly simplifies the calculation. Complete analytical expressions for the amplitudes are presented, which include the contributions from 1-loop triangles "gamma gamma^* H^0" and "gamma Z^* H^0" as well as the W- and Z-boxes with their related $eeH^0$ triangle graphs. The resulting cross section for this mechanism indicates that it could be used to detect the Higgs signal and to test its properties.Comment: 6 pages, 2 figures, RevTe

1/Nc1/N_c Expansion for Excited Baryons

We derive consistency conditions which constrain the possible form of the strong couplings of the excited baryons to the pions. The consistency conditions follow from requiring the pion-excited baryon scattering amplitudes to satisfy the large-N_c Witten counting rules and are analogous to consistency conditions used by Dashen, Jenkins and Manohar and others for s-wave baryons. The consistency conditions are explicitly solved, giving the most general allowed form of the strong vertices for excited baryons in the large-N_c limit. We show that the solutions to the large-N_c consistency conditions coincide with the predictions of the nonrelativistic quark model for these states, extending the results previously obtained for the s-wave baryons. The 1/N_c corrections to these predictions are studied in the quark model with arbitrary number of colors N_c.Comment: 56 pages, REVTeX; one new Appendix added containing a discussion of the results in the language of quark operator

Photon and Z induced heavy charged lepton pair production at a hadron supercollider

We investigate the pair production of charged heavy leptons via photon-induced processes at the proposed CERN Large Hadron Collider (LHC). Using effective photon and Z approximations, rates are given for $L^+L^-$ production due to $\gamma \gamma$ fusion and $Z \gamma$ fusion for the cases of inelastic, elastic and semi-elastic $pp$ collisions. These are compared with the corresponding rates for production via the gluon fusion and Drell-Yan mechanisms. Various $\gamma \gamma$ and $Z \gamma$ differential luminosities for $pp$ collisions are also presented.Comment: 22 pages, RevTex 3.0, 6 uuencoded and compressed postscript figures included. Reference to one paper changed from the original preprint number to the published version. Everything else unchange