3,402 research outputs found
A solvable model of Vlasov-kinetic plasma turbulence in Fourier-Hermite phase space
A class of simple kinetic systems is considered, described by the 1D
Vlasov-Landau equation with Poisson or Boltzmann electrostatic response and an
energy source. Assuming a stochastic electric field, a solvable model is
constructed for the phase-space turbulence of the particle distribution. The
model is a kinetic analog of the Kraichnan-Batchelor model of chaotic
advection. The solution of the model is found in Fourier-Hermite space and
shows that the free-energy flux from low to high Hermite moments is suppressed,
with phase mixing cancelled on average by anti-phase-mixing (stochastic plasma
echo). This implies that Landau damping is an ineffective route to dissipation
(i.e., to thermalisation of electric energy via velocity space). The full
Fourier-Hermite spectrum is derived. Its asymptotics are at low wave
numbers and high Hermite moments () and at low Hermite
moments and high wave numbers (). These conclusions hold at wave numbers
below a certain cut off (analog of Kolmogorov scale), which increases with the
amplitude of the stochastic electric field and scales as inverse square of the
collision rate. The energy distribution and flows in phase space are a simple
and, therefore, useful example of competition between phase mixing and
nonlinear dynamics in kinetic turbulence, reminiscent of more realistic but
more complicated multi-dimensional systems that have not so far been amenable
to complete analytical solution.Comment: 35 pages, minor edits, final version accepted by JP
Making Nuclei Out Of The Skyrme Crystal
A new method for approximating Skyrme solutions is developed. It consists of
cutting sections out of the Skyrme crystal and smoothly interpolating between
the boundary and spatial infinity. Several field configurations are
constructed, and their energies calculated. The surface energy (per unit area)
of an infinite flat plane of the crystal is also calculated, and the result
used to derive a formula analogous to the semi-empirical mass formula of
nuclear physics. This formula can be used to give some idea of what the Skyrme
model predicts about volume and surface energies of the nucleus over a broad
range of baryon numbers.Comment: 20 pages, uuencoded ps file `crystal.uu'. The LaTeX version can be
obtained by emailing [email protected] or [email protected]
A search for massive neutral bosons in orthopositronium decay
We have searched for an exotic decay of orthopositronium into a single photon
and a short-lived neutral boson in the hitherto unexplored mass region above
900 , by noting that this decay is one of few remaining
candidates which could explain the discrepancy of the orthopositronium
decay-rate. A high-resolution measurement of the associated photon energy
spectrum was carried out with a germanium detector to search for a sharp peak
from this two-body decay. Our negative result provides the upper-limits
of\mbox{ } on the branching ratio of such a decay in the
mass region from 847 to 1013 , and excludes the
possibility of this decay mode explaining the discrepancy in the
orthopositronium decay-rate.Comment: a LaTeX file (text 7 pages) and a uuencoded gz-compressed PostScript
file (text 7 pages + figures 4 pages
Composite Skyrme Model with Vector Mesons
We study the composite Skyrme model, proposed by Cheung and G\"{u}rsey,
introducing vector mesons in a chiral Lagrangian. We calculate the static
properties of baryons and compare with results obtained from models without
vector mesons.Comment: LaTeX, 9 pages, 3 figures, to be published in Phys. Rev.
An analytical form of the dispersion function for local linear gyrokinetics in a curved magnetic field
Starting from the equations of collisionless linear gyrokinetics for
magnetised plasmas with an imposed inhomogeneous magnetic field, we present the
first known analytical, closed-form solution for the resulting velocity-space
integrals in the presence of resonances due to both parallel streaming and
constant magnetic drifts. These integrals are written in terms of the
well-known plasma dispersion function (Faddeeva & Terentev 1954; Fried & Conte
1961), rendering the subsequent expressions simpler to treat analytically and
more efficient to compute numerically. We demonstrate that our results converge
to the well-known ones in the straight-magnetic-field and two-dimensional
limits, and show good agreement with the numerical solver by G\"urcan (2014).
By way of example, we calculate the exact dispersion relation for a simple
electrostatic, ion-temperature-gradient-driven instability, and compare it with
approximate kinetic and fluid models.Comment: 35 pages, 13 figure
Infra-Red Finite Charge Propagation
The Coulomb gauge has a long history and many uses. It is especially useful
in bound state applications. An important feature of this gauge is that the
matter fields have an infra-red finite propagator in an on-shell
renormalisation scheme. This is, however, only the case if the renormalisation
point is chosen to be the static point on the mass shell, p = (m, 0, 0, 0). In
this letter we show how to extend this key property of the Coulomb gauge to an
arbitrary relativistic renormalisation point. This is achieved through the
introduction of a new class of gauges of which the Coulomb gauge is a limiting
case. A physical explanation for this result is given.Comment: 8 pages, plain TeX, to appear in Modern Physics Letters
Obituary - Edwin Wallace King
Dr. E.W. King was a highly respected scientist and teacher whose enthusiasm for entomology and general biology has inspired students toward excellence in our discipline for more than 30 years. On December 10, 1984, Dr. King died suddenly of complications associated with cancer
Remarks on the Collective Quantization of the SU(2) Skyrme Model
We point out the question of ordering momentum operator in the canonical
\break quantization of the SU(2) Skyrme Model. Thus, we suggest a new
definition for the momentum operator that may solve the infrared problem that
appears when we try to minimize the Quantum Hamiltonian.Comment: 8 pages, plain tex, IF/UFRJ/9
Baryons and Baryonic Matter in Holographic QCD from Superstring
We study baryons and baryonic matter in holographic QCD using a
D4/D8/ multi-D-brane system in the superstring theory. We obtain
the chiral soliton solution for baryons in the four-dimensional meson theory
derived from the multi-D-brane system. For the analysis of finite
baryon-density matter, we investigate the chiral soliton on in
holographic QCD, and find the delocalization of the soliton, i.e., the swelling
of baryons in dense matter
A Note in the Skyrme Model with Higher Derivative Terms
Another stabilizer term is used in the classical Hamiltonian of the Skyrme
Model that permits in a much simple way the generalization of the higher-order
terms in the pion derivative field. Improved numerical results are obtained.Comment: Latex. Figure not include; available upon request. 7 pages, report
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