1,766 research outputs found

    BOKASUN: a fast and precise numerical program to calculate the Master Integrals of the two-loop sunrise diagrams

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    We present the program BOKASUN for fast and precise evaluation of the Master Integrals of the two-loop self-mass sunrise diagram for arbitrary values of the internal masses and the external four-momentum. We use a combination of two methods: a Bernoulli accelerated series expansion and a Runge-Kutta numerical solution of a system of linear differential equations

    Numerical evaluation of the general massive 2-loop sunrise self-mass master integrals from differential equations

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    The system of 4 differential equations in the external invariant satisfied by the 4 master integrals of the general massive 2-loop sunrise self-mass diagram is solved by the Runge-Kutta method in the complex plane. The method, whose features are discussed in details, offers a reliable and robust approach to the direct and precise numerical evaluation of Feynman graph integrals.Comment: 1+21 pages, Latex, 5 ps-figure

    BHAGEN-1PH: A Monte Carlo event generator for radiative Bhabha scattering

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    BHAGEN-1PH is a FORTRAN program providing fast Monte Carlo event generation of the process e+ee+eγe^+ e^- \to e^+ e^- \gamma, within electroweak theory, for both unpolarized beams and also for the longitudinally polarized electron beam. The program is designed for final leptons outside a small cone around the initial leptons direction and has a new algorithm allowing also for a fast generation of non collinear initial and final emission, as well as for asymmetric and different angular cuts for final leptons.Comment: 23 pages, plain Tex, no figure

    Numerical evaluation of the general massive 2-loop 4-denominator self-mass master integral from differential equations

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    The differential equation in the external invariant p^2 satisfied by the master integral of the general massive 2-loop 4-denominator self-mass diagram is exploited and the expansion of the master integral at p^2=0 is obtained analytically. The system composed by this differential equation with those of the master integrals related to the general massive 2-loop sunrise diagram is numerically solved by the Runge-Kutta method in the complex p^2 plane. A numerical method to obtain results for values of p^2 at and close to thresholds and pseudo-thresholds is discussed in details.Comment: Latex, 20 pages, 7 figure

    Exact Hypothesis Tests for Log-linear Models with exactLoglinTest

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    This manuscript overviews exact testing of goodness of fit for log-linear models using the R package exactLoglinTest. This package evaluates model fit for Poisson log-linear models by conditioning on minimal sufficient statistics to remove nuisance parameters. A Monte Carlo algorithm is proposed to estimate P values from the resulting conditional distribution. In particular, this package implements a sequentially rounded normal approximation and importance sampling to approximate probabilities from the conditional distribution. Usually, this results in a high percentage of valid samples. However, in instances where this is not the case, a Metropolis Hastings algorithm can be implemented that makes more localized jumps within the reference set. The manuscript details how some conditional tests for binomial logit models can also be viewed as conditional Poisson log-linear models and hence can be performed via exactLoglinTest. A diverse battery of examples is considered to highlight use, features and extensions of the software. Notably, potential extensions to evaluating disclosure risk are also considered.

    The Threshold Expansion of the 2-loop Sunrise Selfmass Master Amplitudes

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    The threshold behavior of the master amplitudes for two loop sunrise self-mass graph is studied by solving the system of differential equations, which they satisfy. The expansion at the threshold of the master amplitudes is obtained analytically for arbitrary masses.Comment: 1+18 pages, Latex, no figures, as in Journal reference with more changes in Eq.(31),(42),(45

    Simulation of the process e+ee+eγe^+ e^- \mapsto e^+ e^- \gamma within electroweak theory with longitudinally polarized initial electrons

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    We present simple analytic expressions for the distributions of the Bhabha scattering process with emission of one hard photon, including weak boson exchanges, and with longitudinal polarization of the initial electron. The results from the Monte Carlo generator BHAGEN-1PH, based on these expressions, are presented and compared, for the unpolarized case, with those existing in literature.Comment: 9 pages, plain Tex, no figures, small change in Table

    Refined gluino and squark pole masses beyond leading order

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    The physical pole and running masses of squarks and gluinos have recently been related at two-loop order in a mass-independent renormalization scheme. I propose a general method for improvement of such formulas, and argue that better accuracy results. The improved version gives an imaginary part of the pole mass that agrees exactly with the direct calculation of the physical width at next-to-leading order. I also find the leading three-loop contributions to the gluino pole mass in the case that squarks are heavier, using effective field theory and renormalization group methods. The efficacy of these improvements for the gluino and squarks is illustrated with numerical examples. Some necessary three-loop results for gauge coupling and fermion mass beta functions and pole masses in theories with more than one type of fermion representation, which are not directly accessible from the published literature, are presented in an Appendix.Comment: 14 pages. v2: typos in equations (A.11), (A.17), and (A.18) fixe
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