9,324 research outputs found
Classical integrability of the O(N) nonlinear Sigma model on a half-line
The classical integrability the O(N) nonlinear sigma model on a half-line is
examined, and the existence of an infinity of conserved charges in involution
is established for the free boundary condition. For the case N=3 other possible
boundary conditions are considered briefly.Comment: 12 Pages. Latex file (process twice
On the sine-Gordon--Thirring equivalence in the presence of a boundary
In this paper, the relationship between the sine-Gordon model with an
integrable boundary condition and the Thirring model with boundary is discussed
and the reflection -matrix for the massive Thirring model, which is related
to the physical boundary parameters of the sine-Gordon model, is given. The
relationship between the the boundary parameters and the two formal parameters
appearing in the work of Ghoshal and Zamolodchikov is discussed.Comment: 14 pages, Latex, to be published in Int. J. Mod. Phys. A. Two
references adde
Quantum Spin Hall Effect and Topologically Invariant Chern Numbers
We present a topological description of quantum spin Hall effect (QSHE) in a
two-dimensional electron system on honeycomb lattice with both intrinsic and
Rashba spin-orbit couplings. We show that the topology of the band insulator
can be characterized by a traceless matrix of first Chern integers.
The nontrivial QSHE phase is identified by the nonzero diagonal matrix elements
of the Chern number matrix (CNM). A spin Chern number is derived from the CNM,
which is conserved in the presence of finite disorder scattering and spin
nonconserving Rashba coupling. By using the Laughlin's gedanken experiment, we
numerically calculate the spin polarization and spin transfer rate of the
conducting edge states, and determine a phase diagram for the QSHE.Comment: 4 pages and 4 figure
Enhanced collimated GeV monoenergetic ion acceleration from a shaped foil target irradiated by a circularly polarized laser pulse
Using multi-dimensional particle-in-cell (PIC) simulations we study ion
acceleration from a foil irradiated by a circularly polarized laser pulse at
1022W/cm^2 intensity. When the foil is shaped initially in the transverse
direction to match the laser intensity profile, the center part of the target
can be uniformly accelerated for a longer time compared to a usual flat target.
Target deformation and undesirable plasma heating are effectively suppressed.
The final energy spectrum of the accelerated ion beam is improved dramatically.
Collimated GeV quasi-mono-energetic ion beams carrying as much as 18% of the
laser energy are observed in multi-dimensional simulations. Radiation damping
effects are also checked in the simulations.Comment: 4 pages, 4 figure
Spin Hall Effect and Spin Transfer in Disordered Rashba Model
Based on numerical study of the Rashba model, we show that the spin Hall
conductance remains finite in the presence of disorder up to a characteristic
length scale, beyond which it vanishes exponentially with the system size. We
further perform a Laughlin's gauge experiment numerically and find that all
energy levels cannot cross each other during an adiabatic insertion of the flux
in accordance with the general level-repulsion rule. It results in zero spin
transfer between two edges of the sample as each state always evolves back
after the insertion of one flux quantum, in contrast to the quantum Hall
effect. It implies that the topological spin Hall effect vanishes with the
turn-on of disorder.Comment: 4 pages, 4 figures final versio
Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma
It is shown, by simulation and theory, that circularly or elliptically
polarized terahertz radiation can be generated when a static magnetic (B) field
is imposed on a gas target along the propagation direction of a two-color laser
driver. The radiation frequency is determined by
, where is the
plasma frequency and is the electron cyclotron frequency. With the
increase of the B field, the radiation changes from a single-cycle broadband
waveform to a continuous narrow-band emission. In high-B-field cases, the
radiation strength is proportional to . The B field
provides a tunability in the radiation frequency, spectrum width, and field
strength.Comment: 6 pages, 5 figure
Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects
We investigate how next-generation laser pulses at 10 PW 200 PW interact
with a solid target in the presence of a relativistically underdense preplasma
produced by amplified spontaneous emission (ASE). Laser hole boring and
relativistic transparency are strongly restrained due to the generation of
electron-positron pairs and -ray photons via quantum electrodynamics
(QED) processes. A pair plasma with a density above the initial preplasma
density is formed, counteracting the electron-free channel produced by the hole
boring. This pair-dominated plasma can block the laser transport and trigger an
avalanche-like QED cascade, efficiently transfering the laser energy to
photons. This renders a 1--scalelength, underdense preplasma
completely opaque to laser pulses at this power level. The QED-induced opacity
therefore sets much higher contrast requirements for such pulse in solid-target
experiments than expected by classical plasma physics. Our simulations show for
example, that proton acceleration from the rear of a solid with a preplasma
would be strongly impaired.Comment: 5 figure
Dense blocks of energetic ions driven by multi-petawatt lasers
Laser-driven ion accelerators have the advantages of compact size, high
density, and short bunch duration over conventional accelerators. Nevertheless,
it is still challenging to simultaneously enhance the yield and quality of
laser-driven ion beams for practical applications. Here we propose a scheme to
address this challenge via the use of emerging multi-petawatt lasers and a
density-modulated target. The density-modulated target permits its ions to be
uniformly accelerated as a dense block by laser radiation pressure. In
addition, the beam quality of the accelerated ions is remarkably improved by
embedding the target in a thick enough substrate, which suppresses hot electron
refluxing and thus alleviates plasma heating. Particle-in-cell simulations
demonstrate that almost all ions in a solid-density plasma of a few microns can
be uniformly accelerated to about 25% of the speed of light by a laser pulse at
an intensity around 1022 W/cm2. The resulting dense block of energetic ions may
drive fusion ignition and more generally create matter with unprecedented high
energy density.Comment: 18 pages, 4 figure
Leibniz 2-algebras and twisted Courant algebroids
In this paper, we give the categorification of Leibniz algebras, which is
equivalent to 2-term sh Leibniz algebras. They reveal the algebraic structure
of omni-Lie 2-algebras introduced in \cite{omniLie2} as well as twisted Courant
algebroids by closed 4-forms introduced in \cite{4form}.
We also prove that Dirac structures of twisted Courant algebroids give rise
to 2-term -algebras and geometric structures behind them are exactly
-twisted Lie algebroids introduced in \cite{Grutzmann}.Comment: 22 pages, to appear in Comm. Algebr
- …