5,024 research outputs found

### SUSY-QCD corrections in the squark-gluino sector

A status report is given of the calculations of next-to-leading-order ($N=1$)
supersymmetric QCD corrections to the production of squarks and gluinos in
$p\bar{p}/pp$ collisions. The implementation of these SUSY-QCD corrections
leads to more stable theoretical predictions and to a substantial increase of
the production cross-sections. In addition we give a discussion of the use of
the $\overline{MS}$ scheme for renormalizing the coupling constants in the QCD
sector of ($N=1$) supersymmetric theories.Comment: 6 two-column pages, tar'ed gzip'ed uuencoded files, LaTeX, 7
Encapsulated Postscript figures, uses epsfig and espcrc2. To appear in the
proceedings of the 1996 Zeuthen Workshop on Elementary Particle Theory: "QCD
and QED in Higher Orders", J.Bl\"umlein, F.Jegerlehner, and T.Riemann eds.
Complete postscript file available at
http://rulgm4.LeidenUniv.nl/preprints.htm

### Distribution of the reflection eigenvalues of a weakly absorbing chaotic cavity

The scattering-matrix product SS+ of a weakly absorbing medium is related by
a unitary transformation to the time-delay matrix without absorption. It
follows from this relationship that the eigenvalues of SS+ for a weakly
absorbing chaotic cavity are distributed according to a generalized Laguerre
ensemble.Comment: 4 pages, 1 figure, to appear in Physica E (special issue on Dynamics
of Complex Systems

### Gauge invariant decomposition of 1-loop multiparticle scattering amplitudes

A simple algorithm is presented to decompose any 1-loop amplitude for
scattering processes of the class 2 fermions -> 4 fermions into a fixed number
of gauge-invariant form factors. The structure of the amplitude is simpler than
in the conventional approaches and its numerical evaluation is made faster. The
algorithm can be efficiently applied also to amplitudes with several thousands
of Feynman diagrams.Comment: 6 page

### Light Fermion Mass Effects in e^+e^- -> 4 Fermions

We investigated the effect of the light fermion masses on cross sections for
e^+e^- into 4 fermions in the Fermion Loop scheme defined in hep-ph/9612260,
and approximations to it. The effects are found to be very small, except of
course in the collinear region of single W-boson production where the electron
mass acts as the cut-off.Comment: 8 pages, latex, 3 ps figs include

### Lasing Threshold and Mode Competition in Chaotic Cavities

The lasing threshold is studied of a multi-mode chaotic cavity (linear size D
>> wavelength \lambda) coupled to the outside through a small hole (linear size
d << \lambda). For sufficiently weak absorption by the boundaries, the
statistical distribution of the threshold is wide, its mean value being much
less than the pumping rate needed to compensate the average loss. The average
number N_{nc} >> 1 of non-competing excited modes is proportional to the square
root of the pumping rate. We use the classical model of spatial hole burning to
account for mode competition and find a reduction in the average number of
excited modes to N =3^{1/3} N_{nc}^{2/3}.Comment: 6 pages, RevTeX, 3 figures. Discussion of effects of non-zero
resistivity in the boundaries is adde

### On Large-Angle Bhabha Scattering at LEP

The theoretical accuracy of the program TOPAZ0 in the large-angle Bhabha
channel is estimated. The physical error associated with the full Bhabha cross
section and its forward and backward components separately is given for some
event selections and several energy points of interest for LEP1 physics, both
for the $s$ and non-$s$ contributions to the cross section.Comment: 8 pages, LaTeX, six tables, no figure

### Non-factorizable photonic corrections to ee->WW->4fermions

We study the non-factorizable corrections to W-pair-mediated four-fermion
production in ee annihilation in double-pole approximation. We show how these
corrections can be combined with the known corrections to the production and
the decay of on-shell W-boson pairs, and how the full off-shell Coulomb
singularity is included. Moreover, we find that the actual form of the real
non-factorizable corrections depends on the parametrization of phase space,
more precisely, on the definition of the invariant masses of the resonant W
bosons. For the usual parametrization the full analytical results for the
non-factorizable corrections are presented. Our analytical and numerical
results for the non-factorizable corrections agree with a recent calculation,
which was found to differ from a previous one. The detailed numerical
discussion covers the invariant-mass distribution, various angular
distributions, and the lepton-energy distribution for leptonic final states.Comment: 46 pages, latex, 13 eps figures, incorrect remarks concerning the
universality of non-factorizable corrections to pure invariant-mass
distributions discarde

### Universality of Brezin and Zee's Spectral Correlator

The smoothed correlation function for the eigenvalues of large hermitian
matrices, derived recently by Brezin and Zee [Nucl. Phys. B402 (1993) 613], is
generalized to all random-matrix ensembles of Wigner-Dyson type. Submitted to
Nuclear Physics B[FS].Comment: 6 pages, REVTeX-3.0, INLO-PUB-93100

### Electroweak two-loop Sudakov logarithms for on-shell fermions and bosons

We calculate the virtual electroweak Sudakov (double) logarithms at one- and
two-loop level for arbitrary on-shell/on-resonance particles in the Standard
Model. The associated Sudakov form factors apply in a universal way to
arbitrary non-mass-suppressed electroweak processes at high energies, although
this universality has to be interpreted with care. The actual calculation is
performed in the temporal Coulomb gauge, where the relevant contributions from
collinear-soft gauge-boson exchange are contained exclusively in the
self-energies of the external on-shell/on-resonance particles. In view of the
special status of the time-like components in this gauge, a careful analysis of
the asymptotic states of the theory is required. From this analysis we derive
an all-order version of the Goldstone-boson Equivalence Theorem without the
need for finite compensation factors. By exploiting conditions obtained from
non-renormalization requirements, which are a consequence of our choice of
gauge, we show that the Sudakov corrections can be extracted through a
combination of energy derivatives and projections by means of external sources.
We observe that the Standard Model behaves dynamically like an unbroken theory
in the Sudakov limit, in spite of the fact that the explicit particle masses
are needed at the kinematical (phase-space) level while calculating the Sudakov
form factors.Comment: 55 page

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