2,562 research outputs found
Two-Loop Correction to the Decay Rate
We present the two-loop correction to the decay rate of the Stan\-dard-Model Higgs boson, assuming that the quark
is much heavier than the Higgs boson. Apart from the universal correction
connected with the renormalizations of the wave function and the vacuum
expectation value of the Higgs field, this involves vertex corrections specific
to the presence of beauty in the final state. We calculate the latter by means
of a low-energy theorem. All would-be mass singularities related to the
quark can be absorbed into the running Higgs-bottom Yukawa coupling. It turns
out that the total correction screens the leading
high- behaviour of the one-loop result by 71\% to 75\% for between
60~GeV and .Comment: 16 p., Latex, 2 figures included (uuencoded PS-files), DESY 94-10
Low-Energy Theorems in Higgs Physics
We present low-energy theorems for the calculation of loop amplitudes with
external scalar or pseudoscalar Higgs bosons which are light compared to the
loop particles. Starting from existing lowest-order versions of these theorems,
we show how their applicability may be extended to the two--loop level. To
illustrate the usefulness of these theorems, we discuss a number of
applications to Higgs production and decay at and beyond the one--loop order.Comment: 24 pages, latex, no figure
A study of stress-free living bone and its application to space flight
Observations of animals and human subjects in weightless space flight (Skylab and COSMOS) document altered bone metabolism. Bone metabolism is affected by a number of local and systemic factors. The calcification and growth of transplanted bone is independent of local muscle, nervous, and mechanical forces; therefore, transplanted bone would provide data on the role of local vs. systematic factors. Bone metabolism in living transplanted bone, devoid of stress, was investigated as a possible tool for the investigation of countermeasures against disuse bone loss. An animal model using Sprague-Dawley rats was developed for transplantation of femur bone tissue on a nutrient vascular pedicel. The long term course of these implants was assessed through the measure of regional and total bone mineral, blood flow, and methylene diphosphonate (MDP) uptake. Clomid, an estrogen agonist/antagonist, was shown to protect bone from disuse loss of minerals by retarding trabecular and cortical resorption
HDECAY: a Program for Higgs Boson Decays in the Standard Model and its Supersymmetric Extension
We describe the Fortran code HDECAY which calculates the decay widths and the
branching ratios of the Standard Model Higgs boson, and of the neutral and
charged Higgs particles of the Minimal Supersymmetric extension of the Standard
Model. The program is self-contained (with all subroutines included), easy to
run, fast and calculates the decay widths and branching ratios according to the
current theoretical knowledge.Comment: LaTeX, 26 pages, 3 ps figures include
Large-p_T Photoproduction of D^*+- Mesons in ep Collisions
The cross section for the inclusive photoproduction of large-p_T D^*+- mesons
is calculated at next-to-leading order, adopting different approaches to
describe the fragmentation of charm quarks into D^*+- mesons. We treat the
charm quark according to the massless factorization scheme, where it is assumed
to be one of the active flavours inside the proton and the photon. We present
inclusive single-particle distributions in transverse momentum and rapidity,
including the contributions due to both direct and resolved photons. We compare
and assess the various implementations of fragmentation. We argue that, in the
high-p_T regime, a particularly realistic description can be obtained by
convoluting the Altarelli-Parisi-evolved fragmentation functions of Peterson et
al. with the hard-scattering cross sections of massless partons where the
factorization of the collinear singularities associated with final-state charm
quarks is converted to the massive-charm scheme. The predictions thus obtained
agree well with recent experimental data by the H1 and ZEUS Collaborations at
DESY HERA.Comment: 31 pages (Latex), 13 figures (Postscript). This version of the
manuscript is identical with the one being printed in Z. Phys.
Decays of Supersymmetric Particles: the program SUSY-HIT (SUspect-SdecaY-Hdecay-InTerface)
We present the program package SUSY-HIT for the computation of supersymmetric
particle decays within the framework of the Minimal Supersymmetric extension of
the Standard Model. The code is based on two existing programs HDECAY and
SDECAY for the calculation of the decay widths and branching ratios of,
respectively, the MSSM Higgs bosons and the SUSY particles, and calls a program
for the calculation of the SUSY particle spectrum such as SuSpect. Including
all important higher order effects, the package allows the consistent
calculation of the MSSM particle spectrum and decays with the presently highest
level of precision.Comment: 8 pages, no figure
Search for MSSM Higgses at the Tevatron
We present an overview of searches for MSSM Higgs at the Tevatron,
concentrating on searches probing the high tan(beta) region. We discuss the
search for A/H -> tau tau which is soon to be completed in the Run I data and
review the new tau triggers implemented by CDF and D0 in Run II, which will
greatly impact this analysis. We also present the results of a Run I search for
A/H bb -> bbbb performed by CDF and highlight expected improvements in this
channel by both experiments in Run II.Comment: 3 pages with 1 figure, to be published in "Proceedings of the 31st
International Conference on High Energy Physics ICHEP 2002
Cross Sections for Charm Production in Collisions: Massive versus Massless Scheme
The next--to--leading order inclusive cross section for large-
photoproduction of charm quarks at HERA is calculated in two different
approaches. In the first approach the charm quarks are treated as massive
objects which are strictly external to the proton and the photon while in the
second approach the charm mass is neglected and the quark is assumed to be
one of the active flavours in the proton and photon structure functions. We
present single-inclusive distributions in transverse momentum and rapidity
including direct and resolved photons. The cross section in the massless
approach is found to be significantly larger than in the massive scheme. The
deviation originates from several contributions which are disentangled. We
argue that large- photoproduction of charm quarks at HERA will be
sensitive to the charm content of the photon structure function.Comment: 11 pages, Latex, epsfig, 6 figures appended as uuencoded file
(hardcopy can be obtained upon request from [email protected]
Two-Photon Decay Widths of Higgs Particles
Two--photon decays of Higgs bosons are important channels for the search of
these particles in the intermediate mass range at the colliders LHC and
SSC. Dynamical aspects of the Higgs coupling to two photons can also be studied
by means of the fusion of Higgs particles at high--energy
ee linear colliders. Extending earlier analyses which had been
restricted to the Standard Model, we present in this note the QCD radiative
corrections to the decay widths of scalar and pseudoscalar
Higgs particles in multi--doublet extensions of the Higgs sector, as realized
for instance in supersymmetric theories.Comment: 8pages + 3figures (not included, a hard copy is available from A.D.
upon request), Prep. DESY 92-170 (to appear in Phys. Lett. B
The measurement of the Higgs self-coupling at the LHC: theoretical status
Now that the Higgs boson has been observed by the ATLAS and CMS experiments
at the LHC, the next important step would be to measure accurately its
properties to establish the details of the electroweak symmetry breaking
mechanism. Among the measurements which need to be performed, the determination
of the Higgs self-coupling in processes where the Higgs boson is produced in
pairs is of utmost importance. In this paper, we discuss the various processes
which allow for the measurement of the trilinear Higgs coupling: double Higgs
production in the gluon fusion, vector boson fusion, double Higgs-strahlung and
associated production with a top quark pair. We first evaluate the production
cross sections for these processes at the LHC with center-of-mass energies
ranging from the present TeV to TeV, and discuss
their sensitivity to the trilinear Higgs coupling. We include the various
higher order QCD radiative corrections, at next-to-leading order for gluon and
vector boson fusion and at next-to-next-to-leading order for associated double
Higgs production with a gauge boson. The theoretical uncertainties on these
cross sections are estimated. Finally, we discuss the various channels which
could allow for the detection of the double Higgs production signal at the LHC
and the accuracy on the self-coupling that could be ultimately achieved.Comment: 37 pages, 10 tables, 17 figures. Typos corrected, matches the journal
versio
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