613 research outputs found

### 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 $e^+ e^- \to e^+ e^- \gamma$, 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 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

### 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

### 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

### 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

### Two-loop scalar self-energies and pole masses in a general renormalizable theory with massless gauge bosons

I present the two-loop self-energy functions for scalar bosons in a general
renormalizable theory, within the approximation that vector bosons are treated
as massless or equivalently that gauge symmetries are unbroken. This enables
the computation of the two-loop physical pole masses of scalar particles in
that approximation. The calculations are done simultaneously in the
mass-independent \bar{MS}, \bar{DR}, and \bar{DR}' renormalization schemes, and
with arbitrary covariant gauge fixing. As an example, I present the two-loop
SUSYQCD corrections to squark masses, which can increase the known one-loop
results by of order one percent. More generally, it is now straightforward to
implement all two-loop sfermion pole mass computations in supersymmetry using
the results given here, neglecting only the electroweak vector boson masses
compared to the superpartner masses in the two-loop parts.Comment: 16 pages, 4 figures. v2: typo in eq. (5.30) fixe

### Simulation of the process $e^+ e^- \mapsto e^+ e^- \gamma$ 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

### Strong and Yukawa two-loop contributions to Higgs scalar boson self-energies and pole masses in supersymmetry

I present results for the two-loop self-energy functions for neutral and
charged Higgs scalar bosons in minimal supersymmetry. The contributions given
here include all terms involving the QCD coupling, and those following from
Feynman diagrams involving Yukawa couplings and scalar interactions that do not
vanish as the electroweak gauge couplings are turned off. The impact of these
contributions on the computation of pole masses of the neutral and charged
Higgs scalar bosons is studied in a few examples.Comment: 23 pages, 9 figures, revtex4. New paragraph in introduction, more
explanation of Figure

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