26,345 research outputs found
Relativistic confinement of neutral fermions with a trigonometric tangent potential
The problem of neutral fermions subject to a pseudoscalar potential is
investigated. Apart from the solutions for , the problem is
mapped into the Sturm-Liouville equation. The case of a singular trigonometric
tangent potential () is exactly solved and the
complete set of solutions is discussed in some detail. It is revealed that this
intrinsically relativistic and true confining potential is able to localize
fermions into a region of space arbitrarily small without the menace of
particle-antiparticle production.Comment: 12 page
Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
We present observations of HESS J1640-465 with the Fermi-LAT. The source is
detected with high confidence as an emitter of high-energy gamma-rays. The
spectrum lacks any evidence for the characteristic cutoff associated with
emission from pulsars, indicating that the emission arises primarily from the
pulsar wind nebula. Broadband modeling implies an evolved nebula with a low
magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi
emission exceeds predictions of the broadband model, and has a steeper
spectrum, possibly resulting from a distinct excess of low energy electrons
similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap
Black Hole Scattering from Monodromy
We study scattering coefficients in black hole spacetimes using analytic
properties of complexified wave equations. For a concrete example, we analyze
the singularities of the Teukolsky equation and relate the corresponding
monodromies to scattering data. These techniques, valid in full generality,
provide insights into complex-analytic properties of greybody factors and
quasinormal modes. This leads to new perturbative and numerical methods which
are in good agreement with previous results.Comment: 28 pages + appendices, 2 figures. For Mathematica calculation of
Stokes multipliers, download "StokesNotebook" from
https://sites.google.com/site/justblackholes/techy-zon
Infrared nano-spectroscopy and imaging of collective superfluid excitations in conventional and high-temperature superconductors
We investigate near-field infrared spectroscopy and superfluid polariton
imaging experiments on conventional and unconventional superconductors. Our
modeling shows that near-field spectroscopy can measure the magnitude of the
superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors
with nanoscale spatial resolution. We demonstrate how the same technique can
measure the c-axis plasma frequency, and thus the c-axis superfluid density, of
layered unconventional superconductors with a similar spatial resolution. Our
modeling also shows that near-field techniques can image superfluid surface
mode interference patterns near physical and electronic boundaries. We describe
how these images can be used to extract the collective mode dispersion of
anisotropic superconductors with sub-diffractional spatial resolution.Comment: 11 pages, 8 figure
Phase-field approach to heterogeneous nucleation
We consider the problem of heterogeneous nucleation and growth. The system is
described by a phase field model in which the temperature is included through
thermal noise. We show that this phase field approach is suitable to describe
homogeneous as well as heterogeneous nucleation starting from several general
hypotheses. Thus we can investigate the influence of grain boundaries,
localized impurities, or any general kind of imperfections in a systematic way.
We also put forward the applicability of our model to study other physical
situations such as island formation, amorphous crystallization, or
recrystallization.Comment: 8 pages including 7 figures. Accepted for publication in Physical
Review
Morphological transition between diffusion-limited and ballistic aggregation growth patterns
In this work, the transition between diffusion-limited and ballistic
aggregation models was revisited using a model in which biased random walks
simulate the particle trajectories. The bias is controlled by a parameter
, which assumes the value (1) for ballistic
(diffusion-limited) aggregation model. Patterns growing from a single seed were
considered. In order to simulate large clusters, a new efficient algorithm was
developed. For , the patterns are fractal on the small length
scales, but homogeneous on the large ones. We evaluated the mean density of
particles in the region defined by a circle of radius centered
at the initial seed. As a function of , reaches the asymptotic
value following a power law
with a universal exponent , independent of . The
asymptotic value has the behavior , where . The characteristic crossover length that determines the transition
from DLA- to BA-like scaling regimes is given by ,
where , while the cluster mass at the crossover follows a power
law , where . We deduce the
scaling relations \beta=\n u\gamma and between these
exponents.Comment: 7 pages, 8 figure
The QCD Membrane
In this paper we study spatially quenched, SU(N) Yang-Mills theory in the
large-N limit. The resulting reduced action shows the same formal look as the
Banks-Fischler-Shenker-Susskind M-theory action. The Weyl-Wigner-Moyal symbol
of this matrix model is the Moyal deformation of a p(=2)-brane action. Thus,
the large-N limit of the spatially quenched SU(N) Yang-Mills is seen to
describe a dynamical membrane. By assuming spherical symmetry we compute the
mass spectrum of this object in the WKB approximation.Comment: 14 pages, LaTeX, non figures; accepted for publication in
Class.Quant. Gra
Electron waves in chemically substituted graphene
We present exact analytical and numerical results for the electronic spectra
and the Friedel oscillations around a substitutional impurity atom in a
graphene lattice. A chemical dopant in graphene introduces changes in the
on-site potential as well as in the hopping amplitude. We employ a T-matrix
formalism and find that disorder in the hopping introduces additional
interference terms around the impurity that can be understood in terms of
bound, semi-bound, and unbound processes for the Dirac electrons. These
interference effects can be detected by scanning tunneling microscopy.Comment: 4 pages, 7 figure
Breathers in the elliptic sine-Gordon model
We provide new expressions for the scattering amplitudes in the
soliton-antisoliton sector of the elliptic sine-Gordon model in terms of cosets
of the affine Weyl group corresponding to infinite products of q-deformed gamma
functions. When relaxing the usual restriction on the coupling constants, the
model contains additional bound states which admit an interpretation as
breathers. These breather bound states are unavoidably accompanied by Tachyons.
We compute the complete S-matrix describing the scattering of the breathers
amonst themselves and with the soliton-antisoliton sector. We carry out various
reductions of the model, one of them leading to a new type of theory, namely an
elliptic version of the minimal D(n+1)-affine Toda field theory.Comment: 20 pages, Latex, one eps-figur
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