946 research outputs found
Ultrashort light bullets described by the two-dimensional sine-Gordon equation
By using a reductive perturbation technique applied to a two-level model,
this study puts forward a generic two-dimensional sine-Gordon evolution
equation governing the propagation of femtosecond spatiotemporal optical
solitons in Kerr media beyond the slowly varying envelope approximation. Direct
numerical simulations show that, in contrast to the long-wave approximation, no
collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may
form from adequately chosen few-cycle input spatiotemporal wave forms. In
contrast to the case of quadratic nonlinearity, the light bullets oscillate in
both space and time and are therefore not steady-state lumps
Charged Hydrogenic, Helium and Helium-Hydrogenic Molecular Chains in a Strong Magnetic Field
A non-relativistic classification of charged molecular hydrogenic, helium and
mixed helium-hydrogenic chains with one or two electrons which can exist in a
strong magnetic field G is given. It is shown that for
both cases at the strongest studied magnetic fields the longest
hydrogenic chain contains at most five protons indicating to the existence of
the and ions, respectively. In the case of the
helium chains the longest chains can exist at the strongest studied magnetic
fields with three and four \al-particles for cases, respectively. For
mixed helium-hydrogenic chains the number of heavy centers can reach five for
highest magnetic fields studied. In general, for a fixed magnetic field
two-electron chains are more bound than one-electron ones.Comment: 32 pages, 2 figures, 9 table
Effects of Line-tying on Magnetohydrodynamic Instabilities and Current Sheet Formation
An overview of some recent progress on magnetohydrodynamic stability and
current sheet formation in a line-tied system is given. Key results on the
linear stability of the ideal internal kink mode and resistive tearing mode are
summarized. For nonlinear problems, a counterexample to the recent
demonstration of current sheet formation by Low \emph{et al}. [B. C. Low and
\AA. M. Janse, Astrophys. J. \textbf{696}, 821 (2009)] is presented, and the
governing equations for quasi-static evolution of a boundary driven, line-tied
magnetic field are derived. Some open questions and possible strategies to
resolve them are discussed.Comment: To appear in Phys. Plasma
Renormalized non-modal theory of the kinetic drift instability of plasma shear flows
The linear and renormalized nonlinear kinetic theory of drift instability of
plasma shear flow across the magnetic field, which has the Kelvin's method of
shearing modes or so-called non-modal approach as its foundation, is developed.
The developed theory proves that the time-dependent effect of the finite ion
Larmor radius is the key effect, which is responsible for the suppression of
drift turbulence in an inhomogeneous electric field. This effect leads to the
non-modal decrease of the frequency and growth rate of the unstable drift
perturbations with time. We find that turbulent scattering of the ion gyrophase
is the dominant effect, which determines extremely rapid suppression of drift
turbulence in shear flow
Extra Dimensions: A View from the Top
In models with compact extra dimensions, where the Standard Model fields are
confined to a 3+1 dimensional hyperplane, the production
cross-section at a hadron collider can receive significant contributions from
multiple exchange of KK modes of the graviton. These are carefully computed in
the well-known ADD and RS scenarios, taking the energy dependence of the sum
over graviton propagators into account. Using data from Run-I of the Tevatron,
95% C.L. bounds on the parameter space of both models are derived. For Run-II
of the Tevatron and LHC, discovery limits are estimated.Comment: Typos corrected, references added. 12 pages, LaTeX, 2 ps figure
The Spectral Slope and Kolmogorov Constant of MHD turbulence
The spectral slope of strong MHD turbulence has recently been a matter of
controversy. While Goldreich-Sridhar model (1995) predicts Kolmogorov's -5/3
slope of turbulence, shallower slopes were often reported by numerical studies.
We argue that earlier numerics was affected by driving due to a diffuse
locality of energy transfer in MHD case. Our highest-resolution simulation
(3072^2x1024) has been able to reach the asymptotic -5/3 regime of the energy
slope. Additionally, we found that so-called dynamic alignment, proposed in the
model with -3/2 slope, saturates and therefore can not affect asymptotic slope.
The observation of the asymptotic regime allowed us to measure Kolmogorov
constant C_KA=3.2+-0.2 for purely Alfv\'enic turbulence and C_K=4.1+-0.3 for
full MHD turbulence. These values are much higher than the hydrodynamic value
of 1.64. The larger value of Kolmogorov constant is an indication of a fairly
inefficient energy transfer and, as we show in this Letter, is in theoretical
agreement with our observation of diffuse locality. We also explain what has
been missing in numerical studies that reported shallower slopes.Comment: 5 pages 3 figure
Problem of the noise-noise correlation function in hot non-Abelian plasma
In this work on the basis of Kadomtsev's kinetic fluctuation theory we
present the more general expression for noise-noise correlation function in
effective theory for ultrasoft field modes.Comment: 3 pages, REVTeX
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