5,024 research outputs found

    SUSY-QCD corrections in the squark-gluino sector

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    A status report is given of the calculations of next-to-leading-order (N=1N=1) supersymmetric QCD corrections to the production of squarks and gluinos in ppˉ/ppp\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 MS‾\overline{MS} scheme for renormalizing the coupling constants in the QCD sector of (N=1N=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

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    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

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    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

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    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

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    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

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    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 ss and non-ss contributions to the cross section.Comment: 8 pages, LaTeX, six tables, no figure

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

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    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

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    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

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    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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