9,383 research outputs found
Quantized Non-Abelian Monopoles on S^3
A possible electric-magnetic duality suggests that the confinement of
non-Abelian electric charges manifests itself as a perturbative quantum effect
for the dual magnetic charges. Motivated by this possibility, we study vacuum
fluctuations around a non-Abelian monopole-antimonopole pair treated as point
objects with charges g=\pm n/2 (n=1,2,...), and placed on the antipodes of a
three sphere of radius R. We explicitly find all the fluctuation modes by
linearizing and solving the Yang-Mills equations about this background field on
a three sphere. We recover, generalize and extend earlier results, including
those on the stability analysis of non-Abelian magnetic monopoles. We find that
for g \ge 1 monopoles there is an unstable mode that tends to squeeze magnetic
flux in the angular directions. We sum the vacuum energy contributions of the
fluctuation modes for the g=1/2 case and find oscillatory dependence on the
cutoff scale. Subject to certain assumptions, we find that the contribution of
the fluctuation modes to the quantum zero point energy behaves as -R^{-2/3} and
hence decays more slowly than the classical -R^{-1} Coulomb potential for large
R. However, this correction to the zero point energy does not agree with the
linear growth expected if the monopoles are confined.Comment: 18 pages, 5 figures. Minor changes, reference list update
Giant Magnetic Moments of Nitrogen Stabilized Mn Clusters and Their Relevance to Ferromagnetism in Mn Doped GaN
Using first principles calculations based on density functional theory, we
show that the stability and magnetic properties of small Mn clusters can be
fundamentally altered by the presence of nitrogen. Not only are their binding
energies substantially enhanced, but also the coupling between the magnetic
moments at Mn sites remains ferromagnetic irrespective of their size or shape.
In addition, these nitrogen stabilized Mn clusters carry giant magnetic moments
ranging from 4 Bohr magnetons in MnN to 22 Bohr magnetons in Mn_5N. It is
suggested that the giant magnetic moments of Mn_xN clusters may play a key role
in the ferromagnetism of Mn doped GaN which exhibit a wide range (10K - 940K)
of Curie temperatures
Power counting with one-pion exchange
Techniques developed for handing inverse-power-law potentials in atomic
physics are applied to the tensor one-pion exchange potential to determine the
regions in which it can be treated perturbatively. In S-, P- and D-waves the
critical values of the relative momentum are less than or of the order of 400
MeV. The RG is then used to determine the power counting for short-range
interaction in the presence of this potential. In the P-and D-waves, where
there are no low-energy bound or virtual states, these interactions have
half-integer RG eigenvalues and are substantially promoted relative to naive
expectations. These results are independent of whether the tensor force is
attractive or repulsive. In the 3S1 channel the leading term is relevant, but
it is demoted by half an order compared to the counting for the effective-range
expansion with only a short-range potential. The tensor force can be treated
perturbatively in those F-waves and above that do not couple to P- or D-waves.
The corresponding power counting is the usual one given by naive dimensional
analysis.Comment: 18 pages, RevTeX (further details, explanation added
Removal of terrestrial DOC in aquatic ecosystems of a temperate river network
Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones
Circular dielectric cavity and its deformations
The construction of perturbation series for slightly deformed dielectric
circular cavity is discussed in details. The obtained formulae are checked on
the example of cut disks. A good agreement is found with direct numerical
simulations and far-field experiments.Comment: 17 pages, 12 figure
On separable Fokker-Planck equations with a constant diagonal diffusion matrix
We classify (1+3)-dimensional Fokker-Planck equations with a constant
diagonal diffusion matrix that are solvable by the method of separation of
variables. As a result, we get possible forms of the drift coefficients
providing separability of the
corresponding Fokker-Planck equations and carry out variable separation in the
latter. It is established, in particular, that the necessary condition for the
Fokker-Planck equation to be separable is that the drift coefficients must be linear. We also find the necessary condition for
R-separability of the Fokker-Planck equation. Furthermore, exact solutions of
the Fokker-Planck equation with separated variables are constructedComment: 20 pages, LaTe
Those wonderful elastic waves
We consider in a simple and general way elastic waves in isotropic and
anisotropic media, their polarization, speeds, reflection from interfaces with
mode conversion, and surface waves. Reflection of quasi transverse waves in
anisotropic media from a free surface is shown to be characterized by three
critical angles.Comment: 11 Figures 26 page
Bound-States of the Spinless Salpeter Equation for the PT-Symmetric Generalized Hulthen Potential by the Nikiforov-Uvarov Method
The one-dimensional spinless Salpeter equation has been solved for the
PT-symmetric generalized Hulth\'{e}n potential. The Nikiforov-Uvarov {NU)
method which is based on solving the second-order linear differential equations
by reduction to a generalized equation of hypergeometric type is used to obtain
exact energy eigenvalues and corresponding eigenfunctions. We have investigated
the positive and negative exact bound states of the s-states for different
types of complex generalized Hulthen potentials.Comment: 24 page
Waiting in the Wings: Reflected X-ray Emission from the Homunculus Nebula
We report the first detection of X-ray emission associated with the
Homunculus Nebula which surrounds the supermassive star Eta Carinae. The
emission is characterized by a temperature in excess of 100 MK, and is
consistent with scattering of the time-delayed X-ray flux associated with the
star. The nebular emission is bright in the northwestern lobe and near the
central regions of the Homunculus, and fainter in the southeastern lobe. We
also report the detection of an unusually broad Fe K fluorescent line, which
may indicate fluorescent scattering off the wind of a companion star or some
other high velocity outflow. The X-ray Homunculus is the nearest member of the
small class of Galactic X-ray reflection nebulae, and the only one in which
both the emitting and reflecting sources are distinguishable.Comment: 17 pages, 5 figures, accepted by Ap
Taylor dispersion with absorbing boundaries: A Stochastic Approach
We describe how to solve the problem of Taylor dispersion in the presence of
absorbing boundaries using an exact stochastic formulation. In addition to
providing a clear stochastic picture of Taylor dispersion, our method leads to
closed-form expressions for all the moments of the convective displacement of
the dispersing particles in terms of the transverse diffusion eigenmodes. We
also find that the cumulants grow asymptotically linearly with time, ensuring a
Gaussian distribution in the long-time limit. As a demonstration of the
technique, the first two longitudinal cumulants (yielding respectively the
effective velocity and the Taylor diffusion constant) as well as the skewness
(a measure of the deviation from normality) are calculated for fluid flow in
the parallel plate geometry. We find that the effective velocity and the
skewness (which is negative in this case) are enhanced while Taylor dispersion
is suppressed due to absorption at the boundary.Comment: 4 pages, 1 figur
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