1,767 research outputs found
BOKASUN: a fast and precise numerical program to calculate the Master Integrals of the two-loop sunrise diagrams
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
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
BHAGEN-1PH is a FORTRAN program providing fast Monte Carlo event generation
of the process , 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
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
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
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 within electroweak theory with longitudinally polarized initial electrons
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
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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