35,433 research outputs found
Classical Strongly Coupled QGP: VII. Energy Loss
We use linear response analysis and the fluctuation-dissipation theorem to
derive the energy loss of a heavy quark in the SU(2) classical Coulomb plasma
in terms of the monopole and non-static structure factor. The result is
valid for all Coulomb couplings , the ratio of the mean potential
to kinetic energy. We use the Liouville equation in the collisionless limit to
assess the SU(2) non-static structure factor. We find the energy loss to be
strongly dependent on . In the liquid phase with , the
energy loss is mostly metallic and soundless with neither a Cerenkov nor a Mach
cone. Our analytical results compare favorably with the SU(2) molecular
dynamics simulations at large momentum and for heavy quark masses.Comment: 18 pages, 15 figures. v2: added references, changed title, replaced
figures for Fig. 7, corrected typo
J/psi c\bar{c} production in e+e- and hadronic interactions
Predictions of the nonperturbative Quark Gluon Strings model based on the
1/N-expansion in QCD and string picture of interactions for production of
states containing heavy quarks are considered. Relations between fragmentation
functions for different states are used to predict the fragmentation function
of c-quark to J/psi-mesons. The resulting cross section for J/psi-production in
e+e- annihilation is in a good agreement with recent Belle result. It is argued
that associated production of c\bar{c} states with open charm should give a
substantial contribution to production of these states in hadronic interactions
at very high energies.Comment: 7 pages, 2 figure
Genuine Non-Self-Averaging and Ultra-Slow Convergence in Gelation
In irreversible aggregation processes droplets or polymers of microscopic
size successively coalesce until a large cluster of macroscopic scale forms.
This gelation transition is widely believed to be self-averaging, meaning that
the order parameter (the relative size of the largest connected cluster)
attains well-defined values upon ensemble averaging with no sample-to-sample
fluctuations in the thermodynamic limit. Here, we report on anomalous gelation
transition types. Depending on the growth rate of the largest clusters, the
gelation transition can show very diverse patterns as a function of the control
parameter, which includes multiple stochastic discontinuous transitions,
genuine non-self-averaging and ultra-slow convergence of the transition point.
Our framework may be helpful in understanding and controlling gelation.Comment: 8 pages, 10 figure
Decay of highly-correlated spin states in a dipolar-coupled solid
We have measured the decay of NMR multiple quantum coherence intensities both
under the internal dipolar Hamiltonian as well as when this interaction is
effectively averaged to zero, in the cubic calcium fluoride (CaF2) spin system
and the pseudo one-dimensional system of fluoroapatite. In calcium fluoride the
decay rates depend both on the number of correlated spins in the cluster, as
well as on the coherence number. For smaller clusters, the decays depend
strongly on coherence number, but this dependence weakens as the size of the
cluster increases. The same scaling was observed when the coherence
distribution was measured in both the usual Zeeman or z basis and the x basis.
The coherence decay in the one dimensional fluoroapatite system did not change
significantly as a function of the multiple quantum growth time, in contrast to
the calcium fluoride case. While the growth of coherence orders is severely
restricted in this case, the number of correlated spins should continue to
grow, albeit more slowly. All coherence intensities were observed to decay as
Gaussian functions in time. In all cases the standard deviation of the observed
decay appeared to scale linearly with coherence number.Comment: 7 pages, 9 figures. submitted to PR
Time-division SQUID multiplexers with reduced sensitivity to external magnetic fields
Time-division SQUID multiplexers are used in many applications that require
exquisite control of systematic error. One potential source of systematic error
is the pickup of external magnetic fields in the multiplexer. We present
measurements of the field sensitivity figure of merit, effective area, for both
the first stage and second stage SQUID amplifiers in three NIST SQUID
multiplexer designs. These designs include a new variety with improved
gradiometry that significantly reduces the effective area of both the first and
second stage SQUID amplifiers.Comment: 4 pages, 7 figures. Submitted for publication in the IEEE
Transactions on Applied Superconductivity, August 201
Comment on Decay
We calculate the rate for decay using Chiral
Perturbation Theory. This isospin violating process results from -
mixing, and its amplitude is proportional to . Experimental information on the branching
ratio for can provide insight into the pattern of
violation in radiative decays.Comment: 7 pages with 2 figures not included but available upon request,
CALT-68-191
Purification through Zeno-like Measurements
A series of frequent measurements on a quantum system (Zeno-like
measurements) is shown to result in the ``purification'' of another quantum
system in interaction with the former. Even though the measurements are
performed on the former system, their effect drives the latter into a pure
state, irrespectively of its initial (mixed) state, provided certain conditions
are satisfied.Comment: REVTeX4, 4 pages, 1 figure; to be published in Phys. Rev. Lett.
(2003
Color Reflection Invariance and Monopole Condensation in QCD
We review the quantum instability of the Savvidy-Nielsen-Olesen (SNO) vacuum
of the one-loop effective action of SU(2) QCD, and point out a critical defect
in the calculation of the functional determinant of the gluon loop in the SNO
effective action. We prove that the gauge invariance, in particular the color
reflection invariance, exclude the unstable tachyonic modes from the gluon loop
integral. This guarantees the stability of the magnetic condensation in QCD.Comment: 28 pages, 3 figures, JHEP styl
Magnetic Moments of Heavy Baryons
First non-trivial chiral corrections to the magnetic moments of triplet (T)
and sextet (S^(*)) heavy baryons are calculated using Heavy Hadron Chiral
Perturbation Theory. Since magnetic moments of the T-hadrons vanish in the
limit of infinite heavy quark mass (m_Q->infinity), these corrections occur at
order O(1/(m_Q \Lambda_\chi^2)) for T-baryons while for S^(*)-baryons they are
of order O(1/\Lambda_\chi^2). The renormalization of the chiral loops is
discussed and relations among the magnetic moments of different hadrons are
provided. Previous results for T-baryons are revised.Comment: 11 Latex pages, 2 figures, to be published in Phys.Rev.
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