5,334 research outputs found
New nonlinear structures in a degenerate one-dimensional electron gas
The collective dynamics of nonlinear electron waves in an one-dimensional
degenerate electron gas is treated using the Lagrangian fluid approach. A new
class of solutions with a nontrivial space and time dependence is derived. Both
analytical and numerical results demonstrate the formation of stable,
breather-like modes, provided certain conditions are meet. For large amplitude
of the initial density perturbation, a catastrophic collapse of the plasma
density is predicted, even in the presence of the quantum statistical pressure
and quantum diffraction dispersive effects. The results are useful for the
understanding of the properties of general nonlinear structures in dense
plasmas
Quantum Spheres for OSp_q(1/2)
Using the corepresentation of the quantum supergroup OSp_q(1/2) a general
method for constructing noncommutative spaces covariant under its coaction is
developed. In particular, a one-parameter family of covariant algebras, which
may be interpreted as noncommutative superspheres, is constructed. It is
observed that embedding of the supersphere in the OSp_q(1/2) algebra is
possible. This realization admits infinitesimal characterization a la
Koornwinder. A covariant oscillator realization of the supersphere is also
presented.Comment: 30pages, no figure. to be published in J. Math. Phy
Spectral Properties of Accretion Disks Around Black Holes II -- Sub-Keplerian Flows With and Without Shocks
Close to a black hole, the density of the sub-Keplerian accreting matter
becomes higher compared to a spherical flow due to the presence of a
centrifugal barrier independent of whether or not a standing shock actually
forms. This hot dense flow intercepts soft photons from a cold Keplerian disk
and reprocesses them to form high energy X-rays and gamma rays. We study the
spectral properties of various models of accretion disks where a Keplerian disk
on the equatorial plane may or may not be flanked by a sub-Keplerian disk and
the sub-Keplerian flow may or may not possess standing shocks. From comparison
with the spectra, we believe that the observed properties could be explained
better when both the components (Keplerian and sub-Keplerian) are
simultaneously present close to a black hole, even though the sub-Keplerian
halo component may have been produced out of the Keplerian disk itself at
larger radii. We are able to understand soft and hard states of black hole
candidates, properties of X-ray novae outbursts, and quasi-periodic
oscillations of black hole candidates using these two component models. We fit
spectra of X-ray novae GS1124-68 and GS2000+25 and satisfactorily reproduce the
light curves of these objects.Comment: 15 Latex pages plus 12 figures. Macros included. Astrophysical
Journal (In press
Quantum spin glass and the dipolar interaction
Systems in which the dipolar energy dominates the magnetic interaction, and
the crystal field generates strong anisotropy favoring the longitudinal
interaction terms, are considered. Such systems in external magnetic field are
expected to be a good experimental realization of the transverse field Ising
model. With random interactions this model yields a spin glass to paramagnet
phase transition as function of the transverse field. Here we show that the
off-diagonal dipolar interaction, although effectively reduced, destroys the
spin glass order at any finite transverse field. Moreover, the resulting
correlation length is shown to be small near the crossover to the paramagnetic
phase, in agreement with the behavior of the nonlinear susceptibility in the
experiments on \LHx. Thus, we argue that the in these experiments a
cross-over to the paramagnetic phase, and not quantum criticality, was
observed.Comment: To appear in Phys. Rev. Let
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