4,929 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
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
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
Evaluation of PUF and QKD integration techniques as root of trust in communication systems
Quantum Cryptography could be the next key technology in terms of secure communication, but, as with every new technology, it presents problems that need to be solved in
order to become a reality in daily life. This work discusses the integration of Physical Unclonable Functions (PUFs) as a solution for the authentication of the endpoints in quantum
communication protocols. The use of PUF constructions would allow the authentication
of devices without the need of relying on third parties, and support switched trustworthy quantum communication channels; two unseen features in Quantum Key Distribution
(QKD) until now. We analyze in detail PUF integration within the BB84 protocol, as it
is the foundation for all QKD protocols, and two proposals for an authentication scheme
are made, depending on the connection characteristics of the communication endpoints
and the distance between them. These proposals are then generalized for other types of
QKD protocol. Moreover, different types of PUF are analyzed to conclude which ones are
the most suitable for our purpose.La Criptografía Cuántica podría ser la próxima tecnología clave en relación a la seguridad
de las comunicaciones pero, como toda nueva tecnología, presenta problemas que deben
ser resueltos antes de llegar a ser una realidad en el día a día. Este trabajo discute
la integración de Funciones Físicas No-Clonables (PUFs, por sus siglas en inglés) como
solución a la autenticación de los extremos en un protocolo de comunicación cuántica.
El uso de PUFs permitiría la autenticación de dispositivos sin necesidad de depender de
terceros, además de abrir la posibilidad a la conmutación de canales de comunicación
cuántica; dos características nunca vistas en la Distribución Cuántica de Claves (QKD,
por sus siglas en inglés) hasta ahora. Se analiza en detalle la integración de PUFs en el
protocolo BB84, ya que es la base de todos los protocolos de QKD, y se proponen dos
esquemas de autenticación distintos, atendiendo a las características de los extremos de
la comunicación y la distancia entre ellos. Después, estas propuestas se generalizan para
el resto de protocolos de QKD. Además, se estudian distintos tipos de PUF con el objeto
de encontrar la más adecuada para nuestro propósito.Universidad de Sevilla. Grado en Físic
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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