5,512 research outputs found
Exploring the S-Matrix of Massless Particles
We use the recently proposed generalised on-shell representation for
scattering amplitudes and a consistency test to explore the space of tree-level
consistent couplings in four-dimensional Minkowski spacetime. The extension of
the constructible notion implied by the generalised on-shell representation,
i.e. the possibility to reconstruct at tree level all the scattering amplitudes
from the three-particle ones, together with the imposition of the consistency
conditions at four-particle level, allow to rediscover all the known theories
and their algebra structure, if any. Interestingly, this analysis seems to
leave room for high-spin couplings, provided that at least the requirement of
locality is weakened. We do not claim to have found tree-level consistent
high-spin theories, but rather that our methods show signatures of them and
very likely, with a suitable modification, they can be a good framework to
perform a systematic search.Comment: 44 pages, 1 figur
On the Abundance of Circumbinary Planets
We present here the first observationally based determination of the rate of
occurrence of circumbinary planets. This is derived from the publicly available
Kepler data, using an automated search algorithm and debiasing process to
produce occurrence rates implied by the seven systems already known. These
rates depend critically on the planetary inclination distribution: if
circumbinary planets are preferentially coplanar with their host binaries, as
has been suggested, then the rate of occurrence of planets with
orbiting with \ d is \% (95\% confidence limits),
higher than but consistent with single star rates. If on the other hand the
underlying planetary inclination distribution is isotropic, then this
occurrence rate rises dramatically, to give a lower limit of 47\%. This implies
that formation and subsequent dynamical evolution in circumbinary disks must
either lead to largely coplanar planets, or proceed with significantly greater
ease than in circumstellar disks. As a result of this investigation we also
show that giant planets () are significantly less common in
circumbinary orbits than their smaller siblings, and confirm that the proposed
shortfall of circumbinary planets orbiting the shorter period binaries in the
Kepler sample is a real effect.Comment: Accepted for publication in MNRAS (1st August 2014). 12 pages. Update
to match final version, including clarifications and new figures. Results are
unchange
\pi N scattering in relativistic baryon chiral perturbation theory revisited
We have analyzed pion-nucleon scattering using the manifestly relativistic
covariant framework of Infrared Regularization up to {\cal O}(q^3) in the
chiral expansion, where q is a generic small momentum. We describe the
low-energy phase shifts with a similar quality as previously achieved with
Heavy Baryon Chiral Perturbation Theory, \sqrt{s}\lesssim1.14 GeV. New values
are provided for the {\cal O}(q^2) and {\cal O}(q^3) low-energy constants,
which are compared with previous determinations. This is also the case for the
scattering lengths and volumes. Finally, we have unitarized the previous
amplitudes and as a result the energy range where data are reproduced increases
significantly.Comment: 26 pages, 5 figures, 5 table
Frozen light in photonic crystals with degenerate band edge
Consider a plane monochromatic wave incident on a semi-infinite periodic
structure. What happens if the normal component of the transmitted wave group
velocity vanishes? At first sight, zero normal component of the transmitted
wave group velocity simply implies total reflection of the incident wave. But
we demonstrate that total reflection is not the only possible outcome. Instead,
the transmitted wave can appear in the form of a frozen mode with very large
diverging amplitude and either zero, or purely tangential energy flux. The
field amplitude in the transmitted wave can exceed that of the incident wave by
several orders of magnitude. There are two qualitatively different kinds of
frozen mode regime. The first one is associated with a stationary inflection
point of electromagnetic dispersion relation. This phenomenon has been analyzed
in our previous publications. Now, our focus is on the frozen mode regime
related to a degenerate photonic band edge. An advantage of this new phenomenon
is that it can occur in much simpler periodic structures. This spectacular
effect is extremely sensitive to the frequency and direction of propagation of
the incident plane wave. These features can be very attractive in a variety
practical applications, such as higher harmonic generation and wave mixing,
light amplification and lasing, highly efficient superprizms, etc
Recommended from our members
Chikashsha alhihaat Chikashshanompa\u27 anompoli katihma: Chickasaws are still speaking Chikashshanompa\u27
Holisso mako̲ anompa toklo\u27 ishtiiholissochitok, Chikashshanompa\u27 micha Naahollimanompa\u27. Hopaakikaash Chikashsha mó̲ma\u27at i̲yaakni\u27 sipokni\u27 áyya\u27shattook. 1837aash Naahollo i̲naalhpisa\u27at pomokloshi\u27 wihat kanallichittook. Pomokloshaat Hattak Api\u27ma\u27 I̲yaakni\u27 onat tahattook. Pomanompa\u27at impállaminattookookya kaniya\u27ookya iláyya\u27shakmat Chikashsha ilittimanompohó̲li katihma. Chikashsha alhihaat ittimanompoli aaissa ki\u27yokittook. Chikashsha sipóngni\u27at imanompa\u27 imaabahánchi bÃyyi\u27kanattook. Mako\u27no imaabahánchi katihma. Pomanompa\u27at ikshoka\u27chi imahoobookya ki\u27yokittook. Anompa\u27at tibi\u27 kolofa\u27 chohmittook. Ittonchololit ishtayattook. 2007aash po̲minko\u27 Bill Anoatubbyat Chickasaw Language Revitalization Program ikbittook. Sipóngni\u27, anompa\u27 shaali\u27 cho\u27maat ibaatoksalit ishtayattook. Chikashsha alhihaat Chikashshanompa\u27 anompoli katihma. Pomanompaat bÃlli\u27yacha bÃlli\u27ya. This Chronicle, written in both Chikashshanompa\u27 (Chickasaw language) and English, reflects on the efforts of Chikashsha okla (Chickasaw people) to reclaim and revitalize Chikashshanompa\u27. Over time and for a variety of reasons—including Removal, English-only schooling, intermarriage with non-Chikashsha, and economic depression—many people stopped speaking Chikashshanompa\u27. Still, those who cared deeply for the language tended to it, making it possible for future generations to learn and to speak Chikashshanompa\u27. Because of the Chikashshanompa\u27 revitalization and reclamation work, undertaken by many, Chikashsha alhihaat Chikashshanompa\u27 anompoli katihma—Chickasaws are still speaking Chickasaw
Rigorous formulation of oblique incidence scattering from dispersive media
We formulate a finite-difference time-domain (FDTD) approach to simulate
electromagnetic wave scattering from scatterers embedded in layered dielectric
or dispersive media. At the heart of our approach is a derivation of an
equivalent one-dimensional wave propagation equation for dispersive media
characterized by a linear sum of Debye-, Drude- and Lorentz-type poles. The
derivation is followed by a detailed discussion of the simulation setup and
numerical issues. The developed methodology is tested by comparison with
analytical reflection and transmission coefficients for scattering from a slab,
illustrating good convergence behavior. The case of scattering from a
sub-wavelength slit in a dispersive thin film is explored to demonstrate the
applicability of our formulation to time- and incident angle-dependent analysis
of surface waves generated by an obliquely incident plane wave.Comment: 35 pages, 8 figures, 4 table
Resonances from meson-meson scattering in U(3) CHPT
In this work, the complete one loop calculation of meson-meson scattering
amplitudes within U(3)\otimes U(3) chiral perturbation theory with explicit
resonance states is carried out for the first time. Partial waves are
unitarized from the perturbative calculation employing a non-perturbative
approach based on the N/D method. Once experimental data are reproduced in a
satisfactory way we then study the resonance properties, such as the pole
positions, corresponding residues and their N_C behaviors. The resulting N_C
dependence is the first one in the literature that takes into account the fact
that the \eta_1 becomes the ninth Goldstone boson in the chiral limit for large
N_C. Within this scheme the vector resonances studied, \rho(770), K^*(892) and
\phi(1020), follow an N_C trajectory in agreement with their standard \bar{q}q
interpretation. The scalars f_0(1370), a_0(1450) and K^*(1430) also have for
large N_C a \bar{q}q pole position trajectory and all of them tend to a bare
octet of scalar resonances around 1.4 GeV. The f_0(980) tends asymptotically to
the bare pole position of a singlet scalar resonance around 1 GeV. The \sigma,
\kappa and a_0(980) scalar resonances have a very different N_C behavior. The
case of the \sigma resonance is analyzed with special detail.Comment: 50 pages, 15 figures, 1 table. Enlarged version with more detail
comparisons with previous results in the literature. To match with accepted
version for publicatio
Computation and visualization of Casimir forces in arbitrary geometries: non-monotonic lateral forces and failure of proximity-force approximations
We present a method of computing Casimir forces for arbitrary geometries,
with any desired accuracy, that can directly exploit the efficiency of standard
numerical-electromagnetism techniques. Using the simplest possible
finite-difference implementation of this approach, we obtain both agreement
with past results for cylinder-plate geometries, and also present results for
new geometries. In particular, we examine a piston-like problem involving two
dielectric and metallic squares sliding between two metallic walls, in two and
three dimensions, respectively, and demonstrate non-additive and non-monotonic
changes in the force due to these lateral walls.Comment: Accepted for publication in Physical Review Letters. (Expected
publication: Vol. 99 (8) 2007
Slow wave resonance in periodic stacks of anisotropic layers
We consider transmission band edge resonance in periodic layered structures
involving birefringent layers. Previously we have shown that the presence of
birefringent layers with misaligned in-plane anisotropy can dramatically
enhance the performance of the photonic-crystal Fabry-Perot resonator. It
allows to reduce its size by an order of magnitude without compromising on its
performance. The key characteristic of the enhanced photonic-crystal cavity is
that its Bloch dispersion relation displays a degenerate photonic band edge,
rather than only regular ones. This can be realized in specially arranged
stacks of misaligned anisotropic layers. On the down side, the presence of
birefringent layers results in the Fabry-Perot resonance being coupled only
with one (elliptic) polarization component of the incident wave, while the
other polarization component is reflected back to space. In this paper we show
how a small modification of the periodic layered array can solve the above
fundamental problem and provide a perfect impedance match regardless of the
incident wave polarization, while preserving the giant transmission resonance,
characteristic of a degenerate photonic band edge. Both features are of
critical importance for a variety of practical applications, including
antennas, light amplification, optical and microwave filters, etc.Comment: To be submitted to Phys. Rev.
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