228 research outputs found
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario
The open light gluino window allows non-trivial higher twist gluino
contributions to the proton wave function. Using a two-component model
originally developed for charm hadroproduction, higher twist intrinsic gluino
contributions to final state R-hadron formation are shown to enhance leading
twist production in the forward region. We calculate R-hadron
production at GeV in pp, pBe, and pCu interactions with
light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.Comment: 22 pages, 10 figures, revte
Large-x Parton Distributions
Reliable knowledge of parton distributions at large x is crucial for many
searches for new physics signals in the next generation of collider
experiments. Although these are generally well determined in the small and
medium x range, it has been shown that their uncertainty grows rapidly for
x>0.1. We examine the status of the gluon and quark distributions in light of
new questions that have been raised in the past two years about "large-x"
parton distributions, as well as recent measurements which have improved the
parton uncertainties. Finally, we provide a status report of the data used in
the global analysis, and note some of the open issues where future experiments,
including those planned for Jefferson Labs, might contribute.Comment: LaTeX, 9 pages, 7 figures. Invited talk presented at the ``Workshop
on Nucleon Structure in the High x-Bjorken Region (HiX2000),'' Temple
University, Philadelphia, Pennsylvania, March 30-April 1, 200
Single gluino production in the R-parity lepton number violating MSSM at the LHC
We examine the -violating signal of single gluino production
associated with a charged lepton or neutrino at the large hadron collider
(LHC), in the model of R-parity relaxed supersymmetric model. If the parameters
in the supersymmetric interactions are not too small, and the
mass of gluino is considered in the range from several GeV (as the Lightest
Supersymmetric Particle) to 800 GeV, the cross section of the single gluino
production via Drell-Yan processes can be in the order of
femto barn, and that via gluon fusion in the order of femto
barn. If the gluino decay can be well detected in the CERN LHC, this process
provides a prospective way to probe supersymmetry and violation.Comment: LaTex, 22 pages, 5 EPS file
Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops
The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm3 m-3 for targets of 350 and 700 cm3 m-3 respectively. Temperatures were set to follow outside ambient or outside ambient +4-degrees-C, and hourly means were within 0.5-degrees-C of the target for 92% of the time for target temperatures greater than 6-degrees-C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifical light with natural photoperiod) was 2% greater than the total measured outside over the same period
Effective Two Higgs Doublets in Nonminimal Supersymmetric Models
The Higgs sectors of supersymmetric extensions of the Standard Model have two
doublets in the minimal version (MSSM), and two doublets plus a singlet in two
others: with (UMSSM) and without (NMSSM) an extra U(1)'. A very concise
comparison of these three models is possible if we assume that the singlet has
a somewhat larger breaking scale compared to the electroweak scale. In that
case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models
(THDM), like the MSSM. As expected, the mass of the lightest CP-even neutral
Higgs boson has an upper bound in each case. We find that in the NMSSM, this
bound exceeds not very much that of the MSSM, unless tan(beta) is near one.
However, the upper bound in the UMSSM may be substantially enhanced.Comment: 8 pages, 1 table, 3 figure
Structure of the Quark Propagator at High Temperature
In the high temperature, chirally invariant phase of QCD, the quark
propagator is shown to have two sets of poles with different dispersion
relations. A reflection property in momentum space relates all derivatives at
zero-momentum of the particle and hole energies, the particle and hole damping
rates, and the particle and hole residues. No use is made of perturbation
theory.Comment: 8 pages, Latex twocolum
Effects of R-parity Violation on the Charged Higgs Boson Decays
We calculate one-loop R-parity-violating couplings corrections to the
processes and . We find that the
corrections to the decay mode are generally about
0.1%, and can be negligible. But the corrections to the decay
mode can reach a few percent for the favored parameters.Comment: 17 pages,6 figures. One type error in the title correcte
A New Gauge for Computing Effective Potentials in Spontaneously Broken Gauge Theories
A new class of renormalizable gauges is introduced that is particularly well
suited to compute effective potentials in spontaneously broken gauge theories.
It allows one to keep free gauge parameters when computing the effective
potential from vacuum graphs or tadpoles without encountering mixed propagators
of would-be-Goldstone bosons and longitudinal modes of the gauge field. As an
illustrative example several quantities are computed within the Abelian Higgs
model, which is renormalized at the two-loop level. The zero temperature
effective potential in the new gauge is compared to that in gauge at
the one-loop level and found to be not only easier to compute but also to have
a more convenient analytical structure. To demonstrate renormalizability of the
gauge for the non-Abelian case, the renormalization of an SU(2)-Higgs model
with completely broken gauge group and of an SO(3)-Higgs model with an unbroken
SO(2) subgroup is outlined and renormalization constants are given at the
one-loop level.Comment: 24 pages, figures produced by LaTeX, plain LaTeX, THU-93/16.
(Completely revised. Essential changes. New stuff added. To appear in
Phys.Rev.D.
Deep Inelastic Scattering and Gauge/String Duality
We study deep inelastic scattering in gauge theories which have dual string
descriptions. As a function of we find a transition. For small , the
dominant operators in the OPE are the usual ones, of approximate twist two,
corresponding to scattering from weakly interacting partons. For large ,
double-trace operators dominate, corresponding to scattering from entire
hadrons (either the original `valence' hadron or part of a hadron cloud.) At
large we calculate the structure functions. As a function of Bjorken
there are three regimes: of order one, where the scattering produces only
supergravity states; small, where excited strings are produced; and,
exponentially small, where the excited strings are comparable in size to the
AdS space. The last regime requires in principle a full string calculation in
curved spacetime, but the effect of string growth can be simply obtained from
the world-sheet renormalization group.Comment: 52 pages, 10 figure
A systematic study of J/psi suppression in cold nuclear matter
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi
hadroproduction and leptoproduction data on nuclear targets is carried out.
This allows us to determine the J/psi-nucleon inelastic cross section, whose
knowledge is crucial to interpret the J/psi suppression observed in heavy-ion
collisions, at SPS and at RHIC. The values of sigma are extracted from each
experiment. A clear tension between the different data sets is reported. The
global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller
than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when
the nDS nuclear parton densities are included in the analysis, although we
emphasize that the present uncertainties on gluon (anti)shadowing do not allow
for a precise determination of sigma. Finally, no significant energy dependence
of the J/psi-N interaction is observed, unless strong nuclear modifications of
the parton densities are assumed.Comment: 25 pages, 5 figure
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