78,980 research outputs found
On the formation of current sheets in response to the compression or expansion of a potential magnetic field
The compression or expansion of a magnetic field that is initially potential
is considered. It was recently suggested by Janse & Low [2009, ApJ, 690, 1089]
that, following the volumetric deformation, the relevant lowest energy state
for the magnetic field is another potential magnetic field that in general
contains tangential discontinuities (current sheets). Here we examine this
scenario directly using a numerical relaxation method that exactly preserves
the topology of the magnetic field. It is found that of the magnetic fields
discussed by Janse & Low, only those containing magnetic null points develop
current singularities during an ideal relaxation, while the magnetic fields
without null points relax toward smooth force-free equilibria with finite
non-zero current.Comment: Accepted for publication in Ap
Weak interactions and quasi-stable particle energy loss
We discuss the interplay between electromagnetic energy loss and weak
interactions in the context of quasistable particle particle propagation
through materials. As specific examples, we consider staus, where weak
interactions may play a role, and taus, where they don't.Comment: 4 pages, 4 figures, to appear in the proceedings of the Second
Workshop on TeV Particle Astrophysics (August 2006, Madison, WI
Inferring short-term volatility indicators from Bitcoin blockchain
In this paper, we study the possibility of inferring early warning indicators
(EWIs) for periods of extreme bitcoin price volatility using features obtained
from Bitcoin daily transaction graphs. We infer the low-dimensional
representations of transaction graphs in the time period from 2012 to 2017
using Bitcoin blockchain, and demonstrate how these representations can be used
to predict extreme price volatility events. Our EWI, which is obtained with a
non-negative decomposition, contains more predictive information than those
obtained with singular value decomposition or scalar value of the total Bitcoin
transaction volume
Probing semiclassical magneto-oscillations in the low-field quantum Hall effect
The low-field quantum Hall effect is investigated on a two-dimensional
electron system in an AlGaAs/GaAs heterostructure. Magneto-oscillations
following the semiclassical Shubnikov-de Haas formula are observed even when
the emergence of the mobility gap shows the importance of quantum localization
effects. Moreover, the Lifshitz-Kosevich formula can survive as the oscillating
amplitude becomes large enough for the deviation to the Dingle factor. The
crossover from the semiclassical transport to the description of quantum
diffusion is discussed. From our study, the difference between the mobility and
cyclotron gaps indicates that some electron states away from the Landau-band
tails can be responsible for the semiclassical behaviors under low-field Landau
quantization.Comment: 14 pages, 6 figure
Multiple Scattering Theory for Two-dimensional Electron Gases in the Presence of Spin-Orbit Coupling
In order to model the phase-coherent scattering of electrons in
two-dimensional electron gases in the presence of Rashba spin-orbit coupling, a
general partial-wave expansion is developed for scattering from a cylindrically
symmetric potential. The theory is applied to possible electron flow imaging
experiments using a moveable scanning probe microscope tip. In such
experiments, it is demonstrated theoretically that the Rashba spin-orbit
coupling can give rise to spin interference effects, even for unpolarized
electrons at nonzero temperature and no magnetic field.Comment: 34 pages, 7 figure
Spontaneous current generation in the gapless 2SC phase
It is found that, except chromomagnetic instability, the gapless 2SC phase
also exhibits a paramagnetic response to the perturbation of an external color
neutral baryon current. The spontaneously generated baryon current driven by
the mismatch is equivalent to the one-plane wave LOFF state. We describe the
2SC phase in the nonlinear realization framework, and show that each
instability indicates the spontaneous generation of the corresponding pseudo
Nambu-Golstone current. We show this Nambu-Goldstone currents generation state
covers the gluon phase as well as the one-plane wave LOFF state. We further
point out that, when charge neutrality condition is required, there exists a
narrow unstable LOFF (Us-LOFF) window, where not only off-diagonal gluons but
the diagonal 8-th gluon cannot avoid the magnetic instability. We discuss that
the diagonal magnetic instability in this Us-LOFF window cannot be cured by
off-diagonal gluon condensate in color superconducting phase, and it will also
show up in some constrained Abelian asymmetric superfluid/superconducting
system.Comment: 8 pages, no figure, final version to appear in PR
On the theory of Bose-condensate fluctuations in finite size systems
An asymptotic expansions for the grand partition function of ideal Bose gas
in the canonical ensemble with arbitrary number of particles is obtained. It is
shown that the expressions found are valid in the whole temperature region, the
critical temperature included. A comparison between the asymptotic formulas for
Bose-condensate fluctuations and the exact ones is carried out and their
quantitative agreement is established
Observation of long-lived polariton states in semiconductor microcavities across the parametric threshold
The excitation spectrum around the pump-only stationary state of a polariton
optical parametric oscillator (OPO) in semiconductor microcavities is
investigated by time-resolved photoluminescence. The response to a weak pulsed
perturbation in the vicinity of the idler mode is directly related to the
lifetime of the elementary excitations. A dramatic increase of the lifetime is
observed for a pump intensity approaching and exceeding the OPO threshold. The
observations can be explained in terms of a critical slowing down of the
dynamics upon approaching the threshold and the following onset of the soft
Goldstone mode
A logarithmic generalization of tensor product theory for modules for a vertex operator algebra
We describe a logarithmic tensor product theory for certain module categories
for a ``conformal vertex algebra.'' In this theory, which is a natural,
although intricate, generalization of earlier work of Huang and Lepowsky, we do
not require the module categories to be semisimple, and we accommodate modules
with generalized weight spaces. The corresponding intertwining operators
contain logarithms of the variables.Comment: 39 pages. Misprints corrected. Final versio
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