4,439 research outputs found
Constraining the Randall-Sundrum Model Using Diphoton Production at Hadron Colliders
Virtual effects of gravitons in the production of diphotons at the upgraded
Tevatron and at the LHC are analysed with the idea of probing the parameter
space of the Randall-Sundrum (RS) model. It is shown that this process yields
stringent constraints on the parameter space of the RS model. We show that data
on diphoton production from Tevatron Run II will be sensitive to a masses of
the first graviton resonance in the range of 700-1150 GeV, while at LHC the
mass range probed will be in the region of 3.5 -- 5.5 TeV.Comment: 8 pages, Latex file + 1 ps figur
Charmonium Production at the LHC
The analyses of large transverse momentum charmonium production at the
Tevatron have shown that fragmentation of gluons is an important production
mechanism. We study large- charmonium production in collisions at the
LHC, and find that due to the copious gluon production at this energy, the
gluon fragmentation contribution completely overwhelms the fusion contribution
and the charm quark fragmentation contribution. Our analysis shows that for
production at the LHC, there is a significant event rate even for ~100~GeV. The measurement of the cross-section at such large values of
will provide a very important test of the fragmentation mechanism.Comment: 9 pages including 2 postscript figure
Lh_c
The production cross-section of h_c, the 1P_1 charmonium state, can be
predicted in Non-Relativistic QCD (NRQCD) using heavy-quark symmetry. We show
that at the Large Hadron Collider a large cross-section for this resonance is
predicted and it should be possible to look for the h_c through it decay into
J/psi +pi even with the statistics that will be achieved within a few months of
run-time at the LHC.Comment: 11 pages, LaTeX, 4 figures include
The shear dynamo problem for small magnetic Reynolds numbers
We study large-scale dynamo action due to turbulence in the presence of a
linear shear flow, in the low conductivity limit. Our treatment is
nonperturbative in the shear strength and makes systematic use of both the
shearing coordinate transformation and the Galilean invariance of the linear
shear flow. The velocity fluctuations are assumed to have low magnetic Reynolds
number (Rm) but could have arbitrary fluid Reynolds number. The magnetic
fluctuations are determined to lowest order in Rm by explicit calculation of
the resistive Green's function for the linear shear flow. The mean
electromotive force is calculated and an integro-differential equation is
derived for the time evolution of the mean magnetic field. In this equation,
velocity fluctuations contribute to two different kinds of terms, the C and D
terms, in which first and second spatial derivatives of the mean magnetic
field, respectively, appear inside the spacetime integrals. The contribution of
the D terms is such that the time evolution of the cross-shear components of
the mean field do not depend on any other components excepting themselves.
Therefore, to lowest order in Rm but to all orders in the shear strength, the D
terms cannot give rise to a shear-current assisted dynamo effect. Casting the
integro-differential equation in Fourier space, we show that the normal modes
of the theory are a set of shearing waves, labelled by their sheared
wavevectors. The integral kernels are expressed in terms of the velocity
spectrum tensor, which is the fundamental quantity that needs to be specified
to complete the integro-differential equation description of the time evolution
of the mean magnetic field.Comment: Near-final version; Accepted for publication in the Journal of Fluid
Mechanics; References added; 22 pages, 2 figure
QCD calculation of J/psi+gamma mass distributions
We compute the J/psi+gamma invariant-mass distributions from the QCD
subprocess g + g --> J/psi+gamma. At large masses, this subprocess is the
dominant mechanism for J/psi+gamma production, and data could provide a good
test of QCD. The mass distribution peaks at relatively small masses (3.4 - 4.0
GeV) and the subprocess could, therefore, represent a significant QCD
background to J/psi+gamma decay of heavier charmonia. We also analyze the J/psi
angular distribution in the J/psi+gamma rest frame.Comment: 7 pages LaTex, 4 figures available on request. CERN-TH.6974/93,
ANL-HEP-PR-93.6
Non-perturbative unification in the light of LEP results
We consider an alternative to conventional GUTs originally proposed by
Maiani, Parisi and Petronzio, where owing to the existence of extra fermion
generations at some intermediate scale, the gauge couplings become large at
high energies. We first comment on how the non- supersymmetric version of this
scenario is ruled out; we then consider the two-loop evolution of the couplings
in the supersymmetric extension of this scenario, and check whether such a
scenario is feasible in the light of the precies values of couplings now
available from LEP.Comment: Latex file 7 pages+1 fig. (ps file appended after the latex file),
CERN-TH.6913/9
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