26,277 research outputs found
Global Alfven Wave Heating of the Magnetosphere of Young Stars
Excitation of a Global Alfven wave (GAW) is proposed as a viable mechanism to
explain plasma heating in the magnetosphere of young stars. The wave and basic
plasma parameters are compatible with the requirement that the dissipation
length of GAWs be comparable to the distance between the shocked region at the
star's surface and the truncation region in the accretion disk. A two-fluid
magnetohydrodynamic plasma model is used in the analysis. A current carrying
filament along magnetic field lines acts as a waveguide for the GAW. The
current in the filament is driven by plasma waves along the magnetic field
lines and/or by plasma crossing magnetic field lines in the truncated region of
the disk of the accreting plasma. The conversion of a small fraction of the
kinetic energy into GAW energy is sufficient to heat the plasma filament to
observed temperatures.Comment: Submitted to ApJ, aheatf.tex, 2 figure
Tkachenko polarons in vortex lattices
We analyze the properties of impurities immersed in a vortex lattice formed
by ultracold bosons in the mean field quantum Hall regime. In addition to the
effects of a periodic lattice potential, the impurity is dressed by collective
modes with parabolic dispersion (Tkachenko modes). We derive the effective
polaron model, which contains a marginal impurity-phonon interaction. The
polaron spectral function exhibits a Lorentzian broadening for arbitrarily
small wave vectors even at zero temperature, in contrast with the result for
optical or acoustic phonons. The anomalous damping of Tkachenko polarons could
be detected experimentally using momentum-resolved spectroscopy.Comment: 10 pages, 2 figure
Orthogonality catastrophe and Kondo effect in graphene
Anderson's orthogonality catastrophe in graphene, at energies close to the
Dirac point, is analyzed. It is shown that, in clean systems, the orthogonality
catastrophe is suppressed, due to the vanishing density of states at the Dirac
point. In the presence of preexisting localized states at the Dirac energy, the
orthogonality catastrophe shows similar features to those found in normal
metals with a finite density of states at the Fermi level. The implications for
the Kondo effect induced by magnetic impurities, and for the Fermi edge
singularities in tunneling processes are also discussed.Comment: 7 pages, 7 figure
Gravitomagnetic Moments of the Fundamental Fields
The quadratic form of the Dirac equation in a Riemann spacetime yields a
gravitational gyromagnetic ratio \kappa_S = 2 for the interaction of a Dirac
spinor with curvature. A gravitational gyromagnetic ratio \kappa_S = 1 is also
found for the interaction of a vector field with curvature. It is shown that
the Dirac equation in a curved background can be obtained as the square--root
of the corresponding vector field equation only if the gravitational
gyromagnetic ratios are properly taken into account.Comment: 8 pages, RevTeX Style, no figures, changed presentation -- now
restricted to fields of spin 0, 1/2 and 1 -- some references adde
Mass Generation from Lie Algebra Extensions
Applied to the electroweak interactions, the theory of Lie algebra extensions
suggests a mechanism by which the boson masses are generated without resource
to spontaneous symmetry breaking. It starts from a gauge theory without any
additional scalar field. All the couplings predicted by the Weinberg-Salam
theory are present, and a few others which are nevertheless consistent within
the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included
in the manuscrip
Exact edge singularities and dynamical correlations in spin-1/2 chains
Exact formulas for the singularities of the dynamical structure factor,
S^{zz}(q,omega), of the S=1/2 xxz spin chain at all q and any anisotropy and
magnetic field in the critical regime are derived, expressing the exponents in
terms of the phase shifts which are known exactly from the Bethe ansatz
solution. We also study the long time asymptotics of the self-correlation
function . Utilizing these results to supplement very
accurate time-dependent Density Matrix Renormalization Group (DMRG) for short
to moderate times, we calculate S^{zz}(q,omega) to very high precision.Comment: 4 pages, 1 figure, 1 table, published versio
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