20,851 research outputs found
Enhanced Macroscopic Quantum Tunneling in BiSrCaCuO Intrinsic Josephson Junction Stacks
We have investigated macroscopic quantum tunneling in
BiSrCaCuO intrinsic Josephson junctions at millikelvin
temperatures using microwave irradiation. Measurements show that the escape
rate for uniformly switching stacks of N junctions is about times higher
than that of a single junction having the same plasma frequency. We argue that
this gigantic enhancement of macroscopic quantum tunneling rate in stacks is
boosted by current fluctuations which occur in the series array of junctions
loaded by the impedance of the environment.Comment: 4 pages and 5 figure
Comment on "Remark on the external-field method in QCD sum rules"
It is proved, that suggested by Jin modified formalism in the external-field
method in QCD sum rules exactly coincides with the formalism used before.
Therefore, unlike the claims of ref.1, this formalism cannot improve the
predictability and reliability of external-field sum rule calculations in
comparison with those, done by the standard approach.
PACS number(s): 12.38.Lg, 11.55.HxComment: 5 pages, RevTe
Effect of Light Fermions on the Confinement Transition in QCD-like Theories
Dependence of the confinement transition parameters on the fermion content
provides information on the mechanism of confinement. Recent progress in
lattice gauge theories has allowed to study it for light flavor number and found this transition to shift toward significantly stronger
coupling. We propose an explanation for that: light fermions can occupy the
chromo-magnetic monopoles, via zero modes, making them "distinguishable" and
unsuitable for Bose-Einstein Condensation. Such dilution of unoccuplied
monopoles is compensated by stronger coupling that makes them lighter and more
numerous. We also suggest that flavor-carrying quark-monopole objects account
for the density beyond quark Fermi sphere seen in cold dense phase of
lattice QCD.Comment: 4 pages, 1 figure; few references added; close to the final published
versio
In-medium pion weak decay constants
In nuclear matter, the pion weak decay constant is separated into the two
components corresponding to the time and space components of the
axial-vector current. Using QCD sum rules, we compute the two decay constants
from the pseudoscalar-axial vector correlation function in the matter . It is found that the sum rule for
satisfies the in-medium Gell-Mann--Oakes--Renner (GOR) relation precisely while
the sum rule does not. The sum rule contains the non-negligible
contribution from the dimension 5 condensate in addition to the
in-medium quark condensate. Using standard set of QCD parameters and ignoring
the in-medium change of the pion mass, we obtain MeV at the nuclear
saturation density. The prediction for depends on values of the dimension
5 condensate and on the Borel mass. However, the OPE constrains that , which does not agree with the prediction from the in-medium chiral
perturbation theory. Depending on the value of the dimension 5 condensate,
at the saturation density is found to be in the range MeV
at the Borel mass GeV.Comment: 19 pages including two postscript figures, substantially revise
Spectral asymmetries in nucleon sum rules at finite density
Apparent inconsistencies between different formulations of nucleon sum rules
at finite density are resolved through a proper accounting of asymmetries in
the spectral functions between positive- and negative-energy states.Comment: 10 pages in RevTeX, OSU-090
Spectra of Baryons Containing Two Heavy Quarks in Potential Model
In this work, we employ the effective vertices for interaction between
diquarks (scalar or axial-vector) and gluon where the form factors are derived
in terms of the B-S equation, to obtain the potential for baryons including a
light quark and a heavy diquark. The concerned phenomenological parameters are
obtained by fitting data of mesons instead of the heavy quarkonia.
The operator ordering problem in quantum mechanics is discussed. Our numerical
results indicate that the mass splitting between and
is very small and it is consistent with the heavy quark effective
theory (HQET).Comment: 16 page
A lattice dynamical treatment for the total potential energy of single-walled carbon nanotubes and its applications: relaxed equilibrium structure, elastic properties, and vibrational modes of ultra-narrow tubes
In this paper, we proposed a lattice dynamic treatment for the total
potential energy for single-walled carbon nanotubes (SWCNT's) which is, apart
from a parameter for the non-linear effects, extracted from the vibrational
energy of the planar graphene sheet. Based upon the proposal, we investigated
systematically the relaxed lattice configuration for narrow SWCNT's, the strain
energy, the Young's modulus and Poisson ratio, and the lattice vibrational
properties respected to the relaxed equilibrium tubule structure. Our
calculated results for various physical quantities are nicely in consistency
with existing experimental measurements. Particularly, we verified that the
relaxation effect brings the bond length longer and the frequencies of various
optical vibrational modes softer; Our calculation provides the evidence that
the Young's modulus of armchair tube exceeds that of the planar graphene sheet,
and the large diameter limits of the Young's modulus and Poisson ratio are in
agreement with the experimental values of the graphite; The calculated radial
breathing modes for the ultra narrow tubes with diameter range between 0.2 -
0.5 nm coincide the experimental results and the existing {\it ab initio}
calculations with satisfaction; For narrow tubes of diameter 2 nm, the
calculated frequencies of optical modes in tubule tangential plane as well as
those of radial breathing modes are also in good agreement with the
experimental measurement. In addition, our calculation shows that various
physical quantities of relaxed SWCNT's can actually be expanded in terms of the
chiral angle defined for the correspondent ideal SWCNT's.Comment: 9 pages, 7 figure
Reversible Random Sequential Adsorption of Dimers on a Triangular Lattice
We report on simulations of reversible random sequential adsorption of dimers
on three different lattices: a one-dimensional lattice, a two-dimensional
triangular lattice, and a two-dimensional triangular lattice with the nearest
neighbors excluded. In addition to the adsorption of particles at a rate K+, we
allow particles to leave the surface at a rate K-. The results from the
one-dimensional lattice model agree with previous results for the continuous
parking lot model. In particular, the long-time behavior is dominated by
collective events involving two particles. We were able to directly confirm the
importance of two-particle events in the simple two-dimensional triangular
lattice. For the two-dimensional triangular lattice with the nearest neighbors
excluded, the observed dynamics are consistent with this picture. The
two-dimensional simulations were motivated by measurements of Ca++ binding to
Langmuir monolayers. The two cases were chosen to model the effects of changing
pH in the experimental system.Comment: 9 pages, 10 figure
Strong and Electromagnetic Decays of X(1835) as a Baryonium State
With the assumption that the recently observed X(1835) is a baryonium state
we have studied the strong decays of and the electromagnetic decay of in the framework of effective Lagrangian formalism. In the present
investigation we have included the contributions from the iso-singlet light
scalar resonances but we have not included the isospin violating effect. Our
result for the strong decay of is
smaller than the observed data. The decay width for the radiative decay of
is consistent with the assumption that it decays through
the glueball. In addition, the width for the strong decay of is larger than that of the strong decay of due to the large phase space and coupling constant
. From our investigation, it is not possible to interpret
X(1835) as a baryonium.Comment: Corrected typo
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