6,202 research outputs found
Model solution for volume reflection of relativistic particles in a bent crystal
For volume reflection process in a bent crystal, exact analytic expressions
for positively- and negatively-charged particle trajectories are obtained
within a model of parabolic continuous potential in each interplanar interval,
with the neglect of incoherent multiple scattering. In the limit of the crystal
bending radius greatly exceeding the critical value, asymptotic formulas are
obtained for the particle mean deflection angle in units of Lindhard's critical
angle, and for the final beam profile. Volume reflection of negatively charged
particles is shown to contain effects of rainbow scattering and orbiting,
whereas with positively charged particles none of these effects arise within
the given model. The model predictions are compared with experimental results
and numerical simulations. Estimates of the volume reflection mean angle and
the final beam profile robustness under multiple scattering are performed.Comment: 21 pages, 11 figure
Boundary conditions at spatial infinity for fields in Casimir calculations
The importance of imposing proper boundary conditions for fields at spatial
infinity in the Casimir calculations is elucidated.Comment: 8 pages, 1 figure, submitted to the Proceedings of The Seventh
Workshop QFEXT'05 (Barcelona, September 5-9, 2005
Few-body resonances of unequal-mass systems with infinite interspecies two-body s-wave scattering length
Two-component Fermi and Bose gases with infinitely large interspecies s-wave
scattering length exhibit a variety of intriguing properties. Among these
are the scale invariance of two-component Fermi gases with equal masses, and
the favorable scaling of Efimov features for two-component Bose gases and
Bose-Fermi mixtures with unequal masses. This paper builds on our earlier work
[D. Blume and K. M. Daily, arXiv:1006.5002] and presents a detailed discussion
of our studies of small unequal-mass two-component systems with infinite
in the regime where three-body Efimov physics is absent. We report on
non-universal few-body resonances. Just like with two-body systems on
resonance, few-body systems have a zero-energy bound state in free space and a
diverging generalized scattering length. Our calculations are performed within
a non-perturbative microscopic framework and investigate the energetics and
structural properties of small unequal-mass two-component systems as functions
of the mass ratio , and the numbers and of heavy and
light atoms. For purely attractive Gaussian two-body interactions, we find that
the and systems exhibit three-body and four-body
resonances at mass ratios and 10.4(2), respectively. The
three- and four-particle systems on resonance are found to be large. This
suggests that the corresponding wave function has relatively small overlap with
deeply-bound dimers, trimers or larger clusters and that the three- and
four-body systems on resonance have a comparatively long lifetime. Thus, it
seems feasible that the features discussed in this paper can be probed
experimentally with present-day technology.Comment: 17 pages, 17 figure
Energies of Quantum QED Flux Tubes
In this talk I present recent studies on vacuum polarization energies and
energy densities induced by QED flux tubes. I focus on comparing three and four
dimensional scenarios and the discussion of various approximation schemes in
view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona,
Sept. 2005. To appear in the proceeding
The Response to a Perturbation in the Reflection Amplitude
We apply inverse scattering theory to calculate the functional derivative of
the potential and wave function of a one-dimensional
Schr\"odinger operator with respect to the reflection amplitude .Comment: 16 pages, no figure
KKbar molecules with momentum-dependent interactions
It is shown that the momentum-dependent kaon-antikaon interactions generated
via vector meson exchange from the standard SU_V(3) x SU_A(3) interaction
Lagrangian lead to a non-local potential in coordinate space that can be
incorporated without approximation into a non-relativistic version of the
Bethe-Salpeter wave equation containing a radial-dependent effective kaon mass
appearing in a fully symmetrized kinetic energy operator, in addition to a
local potential. Estimates of the mass and decay widths of f_0(980) and
a_0(980), considered as KKbar molecules of isospin 0 and 1, as well as for
K^+K^- atomic bound states (kaonium) are presented, and compared with previous
studies of a similar nature. It is argued that without a better knowledge of
hadronic form factors it is not possible to distinguish between the molecular
versus elementary particle models for the structure of the light scalar mesons.Comment: 14 pages, 2 tables, 5 figures. Added subsection on s-channel
exchange, additional remarks on the possible effect of gluon exchange, and 1
additional figur
Bound and resonant impurity states in a narrow gaped armchair graphene nanoribbon
An analytical study of discrete and resonant impurity quasi-Coulomb states in
a narrow gaped armchair graphene nanoribbon (GNR) is performed. We employ the
adiabatic approximation assuming that the motions parallel ("slow") and
perpendicular ("fast") to the boundaries of the ribbon are separated
adiabatically. The energy spectrum comprises a sequence of series of
quasi-Rydberg levels relevant to the "slow" motion adjacent from the low
energies to the size-quantized levels associated with the "fast" motion. Only
the series attributed to the ground size-quantized sub-band is really discrete,
while others corresponding to the excited sub-bands consist of quasi-discrete
(Fano resonant) levels of non-zero energetic widths, caused by the coupling
with the states of the continuous spectrum branching from the low lying
sub-bands. In the two- and three-subband approximation the spectrum of the
complex energies of the impurity electron is derived in an explicit form.
Narrowing the GNR leads to an increase of the binding energy and the resonant
width both induced by the finite width of the ribbon. Displacing the impurity
centre from the mid-point of the GNR causes the binding energy to decrease
while the resonant width of the first excited Rydberg series increases. As for
the second excited series their widths become narrower with the shift of the
impurity. A successful comparison of our analytical results with those obtained
by other theoretical and experimental methods is presented. Estimates of the
binding energies and the resonant widths taken for the parameters of typical
GNRs show that not only the strictly discrete but also the some resonant states
are quite stable and could be studied experimentally in doped GNRs
Starspot Jitter in Photometry, Astrometry and Radial Velocity Measurements
Analytical relations are derived for the amplitude of astrometric,
photometric and radial velocity perturbations caused by a single rotating spot.
The relative power of the star spot jitter is estimated and compared with the
available data for Ceti and HD 166435, as well as with numerical
simulations for Ceti and the Sun. A Sun-like star inclined at
i=90\degr at 10 pc is predicted to have a RMS jitter of 0.087 \uas in its
astrometric position along the equator, and 0.38 m s in radial
velocities. If the presence of spots due to stellar activity is the ultimate
limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like
planets in habitable zones is about an order of magnitude higher that the
sensitivity of prospective ultra-precise radial velocity observations of nearby
stars.Comment: accepted in ApJ Letters, Nov. 200
Two and three-dimensional oscillons in nonlinear Faraday resonance
We study 2D and 3D localised oscillating patterns in a simple model system
exhibiting nonlinear Faraday resonance. The corresponding amplitude equation is
shown to have exact soliton solutions which are found to be always unstable in
3D. On the contrary, the 2D solitons are shown to be stable in a certain
parameter range; hence the damping and parametric driving are capable of
suppressing the nonlinear blowup and dispersive decay of solitons in two
dimensions. The negative feedback loop occurs via the enslaving of the
soliton's phase, coupled to the driver, to its amplitude and width.Comment: 4 pages; 1 figur
- …