314 research outputs found
Color-Octet Contributions to Photoproduction
We have calculated the leading color-octet contributions to the production of
particles in photon-proton collisions. Using the values for the
color-octet matrix elements extracted from fits to prompt data at the
Tevatron, we demonstrate that distinctive color-octet signatures should be
visible in photoproduction. However, these predictions appear at
variance with recent experimental data obtained at HERA, indicating that the
phenomenological importance of the color-octet contributions is smaller than
expected from theoretical considerations and suggested by the Tevatron fits.Comment: 10 pages, LaTeX, epsfig, 4 figure
Unparticle Physics in Single Top Signals
We study the single production of top quarks in and
collisions in the context of unparticle physics through the Flavor Violating
(FV) unparticle vertices and compute the total cross sections for single top
production as functions of scale dimension d_{\U}. We find that among all,
LHC is the most promising facility to probe the unparticle physics via single
top quark production processes.Comment: 14 pages, 10 figure
Constraints from Solar and Reactor Neutrinos on Unparticle Long-Range Forces
We have investigated the impact of long-range forces induced by unparticle
operators of scalar, vector and tensor nature coupled to fermions in the
interpretation of solar neutrinos and KamLAND data. If the unparticle couplings
to the neutrinos are mildly non-universal, such long-range forces will not
factorize out in the neutrino flavour evolution. As a consequence large
deviations from the observed standard matter-induced oscillation pattern for
solar neutrinos would be generated. In this case, severe limits can be set on
the infrared fix point scale, Lambda_u, and the new physics scale, M, as a
function of the ultraviolet (d_UV) and anomalous (d) dimension of the
unparticle operator. For a scalar unparticle, for instance, assuming the
non-universality of the lepton couplings to unparticles to be of the order of a
few per mil we find that, for d_UV=3 and d=1.1, M is constrained to be M >
O(10^9) TeV (M > O(10^10) TeV) if Lambda_u= 1 TeV (10 TeV). For given values of
Lambda_u and d, the corresponding bounds on M for vector [tensor] unparticles
are approximately 100 [3/Sqrt(Lambda_u/TeV)] times those for the scalar case.
Conversely, these results can be translated into severe constraints on
universality violation of the fermion couplings to unparticle operators with
scales which can be accessible at future colliders.Comment: 13 pages, 3 figures. Minor changes due to precision in numerical
factors and correction in figure labels. References added. Conclusions remain
unchange
Laboratory Diagnosis of SARS
The virologic test results of 415 patients with severe acute respiratory syndrome (SARS) were examined. The peak detection rate for SARS-associated coronavirus occurred at week 2 after illness onset for respiratory specimens, at weeks 2 to 3 for stool or rectal swab specimens, and at week 4 for urine specimens. The latest stool sample that was positive by reverse transcriptionâpolymerase chain reaction (RT-PCR) was collected on day 75 while the patient was receiving intensive care. Tracheal aspirate and stool samples had a higher diagnostic yield (RT-PCR average positive rate for first 2 weeks: 66.7% and 56.5%, respectively). Pooled throat and nasal swabs, rectal swab, nasal swab, throat swab, and nasopharyngeal aspirate specimens provided a moderate yield (29.7%â40.0%), whereas throat washing and urine specimens showed a lower yield (17.3% and 4.5%). The collection procedures for stool and pooled nasal and throat swab specimens were the least likely to transmit infection, and the combination gave the highest yield for coronavirus detection by RT-PCR. Positive virologic test results in patient groups were associated with mechanical ventilation or death (p < 0.001), suggesting a correlation between viral load and disease severity
How large could the R-parity violating couplings be?
We investigate in detail the predictions coming from the d=4 operators for
proton decay. We find the most general constraints for the R-parity violating
couplings coming from proton decay, taking into account all fermion mixing and
in different supersymmetric scenarios.Comment: 8 pages, several corrections, to appear in J.Phys.G (2005
Can we distinguish between h^{SM} and h^0 in split supersymmetry?
We investigate the possibility to distinguish between the Standard Model
Higgs boson and the lightest Higgs boson in Split Supersymmetry. We point out
that the best way to distinguish between these two Higgs bosons is through the
decay into two photons. It is shown that there are large differences of several
percent between the predictions for \Gamma(h\to\gamma\gamma) in the two models,
making possible the discrimination at future photon-photon colliders. Once the
charginos are discovered at the next generation of collider experiments, the
well defined predictions for the Higgs decay into two photons will become a
cross check to identify the light Higgs boson in Split Supersymmetry.Comment: 8 pages, 3 Figures, typos fixed, version published in J.Phys. G31
(2005) 563-56
Higgs decay to dark matter in low energy SUSY: is it detectable at the LHC ?
Due to the limited statistics so far accumulated in the Higgs boson search at
the LHC, the Higgs boson property has not yet been tightly constrained and it
is still allowed for the Higgs boson to decay invisibly to dark matter with a
sizable branching ratio. In this work, we examine the Higgs decay to neutralino
dark matter in low energy SUSY by considering three different models: the
minimal supersymmetric standard model (MSSM), the next-to-minimal
supersymmetric standard models (NMSSM) and the nearly minimal supersymmetric
standard model (nMSSM). Under current experimental constraints at 2-sigma level
(including the muon g-2 and the dark matter relic density), we scan over the
parameter space of each model. Then in the allowed parameter space we calculate
the branching ratio of the SM-like Higgs decay to neutralino dark matter and
examine its observability at the LHC by considering three production channels:
the weak boson fusion VV->h, the associated production with a Z-boson pp->hZ+X
or a pair of top quarks pp->htt_bar+X. We find that in the MSSM such a decay is
far below the detectable level; while in both the NMSSM and nMSSM the decay
branching ratio can be large enough to be observable at the LHC.Comment: Version in JHE
Prompt J/psi production at e^+e^- colliders
In this paper, we discuss the prompt j/psi production at e^+e^- colliders via
color-singlet and color-octet production mechanisms. The color-singlet
production processes include 1) e^+e^- to J/\psi gg; 2) e^+e^- to J/\psi
c\bar{c}; 3) e^+e^- to q \bar q ggJ/\psi and e^+e^- to q \bar q g\chi_c
followed by \chi_c to J/\psi \gamma. The color-octet production processes
include 1) e^+e^- to J/\psi g; 2) e^+e^- to j/psi q\bar q. Of all these
production channels, we find that the color-octet contributions dominate over
the color-singlet contributions at any energy scales. At low energies
(\sqrt{s}< 20 GeV), the dominant channel is e^+e^- to J/\psi g whereas at high
energies e+e^- to j/psi q\bar q will take the leading part. We also find that
the energy spectrum for the color-octet j/psi production in process e^+e^- to
j/psi q\bar q is very soft, and the mean energy of the produced j/psi is only
about 10 GeV~ 20 GeV even at very high energies (e.g. at 1000 GeV). The
extraction of color-octet matrix elements from j/psi production in e^+e^-
collisions is also discussed.Comment: 15 page, LaTex, 9 figures in postscript. Submitted to Phys. Rev.
Production of Weak Bosons and Higgs Bosons at e-e- Colliders
We present calculations of cross sections for single and production
and , and pair production within the
Standard Model at linear colliders. We evaluate Standard-Model Higgs
boson production in the channels , , and
. We also illustrate the enhancements in the cross section
that would result from a strongly-interacting Higgs sector or from a
resonance in a Higgs doublet + triplet model.Comment: Standard Latex, 19 pages of text. 11 postscript figures included;
hardcopies by fax or mail available upon request. MAD/PH/77
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