4,142 research outputs found
Bound states on the lattice with partially twisted boundary conditions
We propose a method to study the nature of exotic hadrons by determining the
wave function renormalization constant from lattice simulations. It is
shown that, instead of studying the volume-dependence of the spectrum, one may
investigate the dependence of the spectrum on the twisting angle, imposing
twisted boundary conditions on the fermion fields on the lattice. In certain
cases, e.g., the case of the bound state which is addressed in detail, it
is demonstrated that the partial twisting is equivalent to the full twisting up
to exponentially small corrections
Trajectory-dependent energy loss for swift He atoms axially scattered off a silver surface
Angle- and energy-loss- resolved distributions of helium atoms grazingly
scattered from a Ag(110) surface along low indexed crystallographic directions
are investigated considering impact energies in the few keV range. Final
projectile distributions are evaluated within a semi-classical formalism that
includes dissipative effects due to electron-hole excitations through a
friction force. For mono-energetic beams impinging along the ,
and directions, the model predicts the presence of
multiple peak structures in energy-loss spectra. Such structures provide
detailed information about the trajectory-dependent energy loss. However, when
the experimental dispersion of the incident beam is taken into account, these
energy-loss peaks are completely washed out, giving rise to a smooth
energy-loss distribution, in fairly good agreement with available experimental
data
Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light
It is theoretically shown that nanometric silver lamellar gratings present
very strong visible light absorption inside the grooves, leading to electric
field intensities by several orders of magnitude larger than that of the
impinging light. This effect, due to the excitation of long wave vector surface
plasmon polaritons with particular small penetration depth in the metal, may
explain the abnormal optical absorption observed a long time ago on almost flat
Ag films. Surface enhanced Raman scattering in rough metallic films could also
be due to the excitation of such plasmon polaritons in the grain boundaries or
notches of the films.Comment: 5 pages, 5 figure, submitted to Phys. Rev. Let
The Inverse Amplitude Method and Adler Zeros
The Inverse Amplitude Method is a powerful unitarization technique to enlarge
the energy applicability region of Effective Lagrangians. It has been widely
used to describe resonances from Chiral Perturbation Theory as well as for the
Strongly Interacting Symmetry Breaking Sector. In this work we show how it can
be slightly modified to account also for the sub-threshold region,
incorporating correctly the Adler zeros required by chiral symmetry and
eliminating spurious poles. These improvements produce negligible effects on
the physical region.Comment: 17 pages, 4 figure
Efficient excitation of cavity resonances of subwavelength metallic gratings
One dimensional rectangular metallic gratings enable enhanced transmission of
light for specific resonance frequencies. Two kinds of modes participating to
enhanced transmission have already been demonstrated : (i) waveguide modes and
(ii) surface plasmon polaritons (SPP). Since the original paper of Hessel and
Oliner \cite{hessel} pointing out the existence of (i), no progress was made in
their understanding. We present here a carefull analysis, and show that the
coupling between the light and such resonances can be tremendously improved
using an {\it evanescent} wave. This leads to enhanced localisation of light in
cavities, yielding, in particular, to a very selective light transmission
through these gratings.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
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