69 research outputs found
Energy loss in perturbative QCD
We review the properties of energetic parton propagation in hot or cold QCD
matter, as obtained in recent works. Advances in understanding the energy loss
- collisional and radiative - are summarized, with emphasis on the latter: it
features very interesting properties which may help to detect the quark-gluon
plasma produced in heavy ion collisions. We describe two different theoretical
approaches, which lead to the same radiated gluon energy spectrum. The case of
a longitudinally expanding QCD plasma is investigated. The energy lost by a jet
with given opening angle is calculated in view of making predictions for the
suppression (quenching) of hard jet production. Phenomenological implications
for the difference between hot and cold matter are discussed. Numerical
estimates of the loss suggest that it may be significantly enhanced in hot
compared to cold matter.Comment: 49 pages latex file with 11 embedded PS figures. Uses ar.sty
(included), one equation revised. submitted to Annual Review of Nuclear and
Particle Scienc
CHY representations for gauge theory and gravity amplitudes with up to three massive particles
We show that a wide class of tree-level scattering amplitudes involving
scalars, gauge bosons, and gravitons, up to three of which may be massive, can
be expressed in terms of a Cachazo-He-Yuan representation as a sum over
solutions of the scattering equations. These amplitudes, when expressed in
terms of the appropriate kinematic invariants, are independent of the masses
and therefore identical to the corresponding massless amplitudes.Comment: 20 pages, 1 figure; v2: minor typos corrected, published versio
Density Matrix Kinetic Equation Describing a Passage of Fast Atomic Systems Through Matter
The quantum-mechanical consideration of a passage of fast dimesoatoms through
matter is given. A set of quantum-kinetic equations for the density matrix
elements describing their internal state evolution is derived. It is shown that
probabilistic description of internal dynamics of hydrogen-like atoms is
impossible even at sufficiently low energies because of the ``accidental''
degeneracy of their energy levels.Comment: 12 pages, LATEX, submitted to J. Phys.
Coherent bremsstrahlung, boherent pair production, birefringence and polarimetry in the 20-170 GeV energy range using aligned crystals
The processes of coherent bremsstrahlung (CB) and coherent pair production
(CPP) based on aligned crystal targets have been studied in the energy range
20-170 GeV. The experimental arrangement allowed for measurements of single
photon properties of these phenomena including their polarization dependences.
This is significant as the theoretical description of CB and CPP is an area of
active theoretical debate and development. With the theoretical approach used
in this paper both the measured cross sections and polarization observables are
predicted very well. This indicates a proper understanding of CB and CPP up to
energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to
determine the polarization parameters in our measurements. New technologies for
high energy photon beam optics including phase plates and polarimeters for
linear and circular polarization are demonstrated in this experiment. Coherent
bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger
enhancement for hard photons than CB for the channeling orientations of the
crystal. Our measurements and our calculations indicate low photon
polarizations for the high energy SOS photons.Comment: 23 pages, 27 figures, 2 tables, REVTeX4 two column
Factorization and polarization in linearized gravity
We investigate all the four-body graviton interaction processes:
, , and with
as an elementary particle of spin less than two in the context of linearized
gravity except the spin-3/2 case. We show explicitly that gravitational gauge
invariance and Lorentz invariance cause every four-body graviton scattering
amplitude to be factorized. We explore the implications of this factorization
property by investigating polarization effects through the covariant density
matrix formalism in each four-body graviton scattering process.Comment: 45 pages, figures are included (uses pictex), RevTe
Determination of Leptoquark Properties in Polarized Collisions
We study leptoquark production using polarized colliders for the
center of mass energies ~GeV and 1~TeV. We show that using
polarization asymmetries the ten different types of leptoquarks listed by
Buchm\"uller, R\"uckl and Wyler can be distinquished from one another for
leptoquark masses essentially up to the kinematic limit of the respective
colliders. Thus, if a leptoquark were discovered an collider could
play a crucial role in determining its origins.Comment: 10 pages (plus 10 postscript figures submitted separately), OCIP/C
94-
Prognostic value of Dicer expression in human breast cancers and association with the mesenchymal phenotype
Background: Dicer, a ribonuclease, is the key enzyme required for the biogenesis of microRNAs and small interfering RNAs and is essential for both mammalian development and cell differentiation. Recent evidence indicates that Dicer may also be involved in tumourigenesis. However, no studies have examined the clinical significance of Dicer at both the RNA and the protein levels in breast cancer.Methods: In this study, the biological and prognostic value of Dicer expression was assessed in breast cancer cell lines, breast cancer progression cellular models, and in two well-characterised sets of breast carcinoma samples obtained from patients with long-term follow-up using tissue microarrays and quantitative reverse transcription-PCR.Results: We have found that Dicer protein expression is significantly associated with hormone receptor status and cancer subtype in breast tumours (ER P=0.008; PR P=0.019; cancer subtype P=0.023, luminal A P=0.0174). Dicer mRNA expression appeared to have an independent prognostic impact in metastatic disease (hazard ratio=3.36, P=0.0032). In the breast cancer cell lines, lower Dicer expression was found in cells harbouring a mesenchymal phenotype and in metastatic bone derivatives of a breast cancer cell line. These findings suggest that the downregulation of Dicer expression may be related to the metastatic spread of tumours.Conclusion: Assessment of Dicer expression may facilitate prediction of distant metastases for patients suffering from breast cancer
Triple Electroweak Gauge-Boson Production at Fermilab Tevatron Energies
We calculate the three gauge-boson production in the Standard Model at
Fermilab Tevatron energies. At TeV in collisions, the
cross sections for the triple gauge-boson production are typically of order 10
femtobarns (fb). For the pure leptonic final states from the gauge-boson decays
and with some minimal cuts on final state photons, the cross sections for and
processes are of order a few fb, resulting in a few dozen clean leptonic events
for an integrated luminosity of 10 fb. The pure leptonic modes from
other gauge-boson channels give significantly smaller rate. Especially, the
trilepton modes from and
yield a cross section of order 0.1 fb if there is no significant Higgs boson
contribution. For a Higgs boson with , the triple
massive-gauge-boson production rate could be enhanced by a factor of .Comment: RevTeX 3.0; 14 pages plus 7 figures; ps files available via anonymous
ftp at ftp://ucdhep.ucdavis.edu/han/vvv/vvv.ps,fig*_vvv.p
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