18,873 research outputs found
Spin Sum Rules at Low
Recent precision spin-structure data from Jefferson Lab have significantly
advanced our knowledge of nucleon structure at low . Results on the
neutron spin sum rules and polarizabilities in the low to intermediate
region are presented. The Burkhardt-Cuttingham Sum Rule was verified within
experimental uncertainties. When comparing with theoretical calculations,
results on spin polarizability show surprising disagreements with Chiral
Perturbation Theory predictions. Preliminary results on first moments at very
low are also presented.Comment: 4 pages, to be published in the Proceedings of the 10th Conference on
Intersections of Nuclear and Particle Physics (CIPANP
Tunneling with the Lorentz Force and the Friction
We present a semiclassical study of a transport process, the tunneling, in
the presence of a magnetic field and a dissipative environment. We have found
that the problem can be mapped onto an effective one-dimensional one, and the
tunneling rate is strongly affected by the magnetic field, such as a complete
suppression by a large parallel magnetic field, an example of the dynamical
localization. In such case a small perpendicular component of the field, or the
dissipation, can enhance the tunneling rate. In the small parallel field and
finite temperatures the tunneling rate is finite. Explicit expressions will be
presented in those cases. If viewing the tunneling in the presence of a
magnetic field as a dissipative tunneling process, by varying the magnetic
field and the potential one can obtain the dissipative spectral function
between the subohmic and the superohmic . In combination
with a real dissipative spectral function, the effect of the magnetic field can
map the spectral function from to , with mapping to ,
revealing a dual symmetry between the friction and the Lorentz force. Two cases
relevant to experiments, the edge state tunneling in a Hall bar and the
tunneling near the dynamical localization will be discussed in detail.Comment: Late
A Unified Gravity-Electroweak Model Based on a Generalized Yang-Mills Framework
Gravitational and electroweak interactions can be unified in analogy with the
unification in the Weinberg-Salam theory. The Yang-Mills framework is
generalized to include space-time translational group T(4), whose generators
T_{\mu}(=\p/\p x^{\mu}) do not have constant matrix representations. By
gauging in flat space-time, we have a new
tensor field which universally couples to all particles and
anti-particles with the same constant , which has the dimension of length.
In this unified model, the T(4) gauge symmetry dictates that all wave equations
of fermions, massive bosons and the photon in flat space-time reduce to a
Hamilton-Jacobi equation with the same `effective Riemann metric tensor' in the
geometric-optics limit. Consequently, the results are consistent with
experiments. We demonstrated that the T(4) gravitational gauge field can be
quantized in inertial frames.Comment: 12 pages. To be published in "Modern Physics Letters A
Phase transition in site-diluted Josephson junction arrays: A numerical study
We numerically investigate the intriguing effects produced by random
percolative disorder in two-dimensional Josephson-junction arrays. By dynamic
scaling analysis, we evaluate critical temperatures and critical exponents with
high accuracy. It is observed that, with the introduction of site-diluted
disorder, the Kosterlitz-Thouless phase transition is eliminated and evolves
into a continuous transition with power-law divergent correlation length.
Moreover, genuine depinning transition and creep motion are studied, evidence
for distinct creep motion types is provided. Our results not only are in good
agreement with the recent experimental findings, but also shed some light on
the relevant phase transitions.Comment: 7 pages, 8 figures, Phys. Rev. B (in press
Measuring the equation of state of trapped ultracold bosonic systems in an optical lattice with in-situ density imaging
We analyze quantitatively how imaging techniques with single-site resolution
allow to measure thermodynamical properties that cannot be inferred from
time-of-light images for the trapped Bose-Hubbard model. If the normal state
extends over a sufficiently large range, the chemical potential and the
temperature can be extracted from a single shot, provided the sample is in
thermodynamic equilibrium. When the normal state is too narrow, temperature is
low but can still be extracted using the fluctuation-dissipation theorem over
the entire trap range as long as the local density approximation remains valid,
as was recently suggested by Qi Zhou and Tin-Lun Ho [arXiv:0908.3015]. However,
for typical present-day experiments, the number of samples needed is of the
order of 1000 in order to get the temperature at least accurate, but it
is possible to reduce the variance by 2 orders of magnitude if the
density-density correlation length is short, which is the case for the
Bose-Hubbard model. Our results provide further evidence that cold gases in an
optical lattices can be viewed as quantum analog computers.Comment: 8 pages, 10 figure
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