8,670 research outputs found
Radiative corrections in bumblebee electrodynamics
We investigate some quantum features of the bumblebee electrodynamics in flat
spacetimes. The bumblebee field is a vector field that leads to a spontaneous
Lorentz symmetry breaking. For a smooth quadratic potential, the massless
excitation (Nambu-Goldstone boson) can be identified as the photon, transversal
to the vacuum expectation value of the bumblebee field. Besides, there is a
massive excitation associated with the longitudinal mode and whose presence
leads to instability in the spectrum of the theory. By using the
principal-value prescription, we show that no one-loop radiative corrections to
the mass term is generated. Moreover, the bumblebee self-energy is not
transverse, showing that the propagation of the longitudinal mode can not be
excluded from the effective theory.Comment: Revised version: contains some more elaborated interpretation of the
results. Conclusions improve
Regular string-like braneworlds
In this work, we propose a new class of smooth thick string-like braneworld
in six dimensions. The brane exhibits a varying brane-tension and an
asymptotic behavior. The brane-core geometry is parametrized by the Bulk
cosmological constant, the brane width and by a geometrical deformation
parameter. The source satisfies the dominant energy condition for the
undeformed solution and has an exotic asymptotic regime for the deformed
solution. This scenario provides a normalized massless Kaluza-Klein mode for
the scalar, gravitational and gauge sectors. The near-brane geometry allows
massive resonant modes at the brane for the state and nearby the brane for
.Comment: 14 pages, 12 figures. Some modifications to match the published
version in EPJ
Gauge fields in a string-cigar braneworld
In this work we investigate the properties of an Abelian gauge vector field
in a thin and in a smoothed string-like braneworld, the so-called string-cigar
model. This thick brane scenario satisfies the regularity conditions and it can
be regarded as an interior and exterior string-like solution. The source
undergoes a geometric Ricci flow which is connected to a variation of the bulk
cosmological constant. The Ricci flow changes the width and amplitude of the
massless mode at the brane core and recover the usual thin string-like behavior
at large distances. By numerical means we obtain the Kaluza-Klein (KK) spectrum
for both the thin brane and the string-cigar. It turns out that both models
exhibit a mass gap between the massless and the massive modes and between the
high and the low mass regimes. The KK modes are smooth near the brane and their
amplitude are enhanced by the string-cigar core. The analogue Schr\"odinger
potential is also tuned by the geometric flow.Comment: The discussion about the Kaluza-Klein spectrum of the gauge field was
improved. Numerical analysis was adapted to the conventional notation on
Kaluza-Klein number. Some graphics were modified for considering other
notation. Results unchanged. References added. Corrected typos. 17 pages. 6
figures. To match version to appears in Physics Letters
ROAZ Autonomous Surface Vehicle Design and Implementation
The design of an Autonomous Surface Vehicle for operation in river and
estuarine scenarios is presented. Multiple operations with autonomous underwater
vehicles and support to AUV missions are one of the main design goals in the ROAZ
system. The mechanical design issues are discussed. Hardware, software and
implementation status are described along with the control and navigation system
architecture. Some preliminary test results concerning a custom developed thruster are
presented along with hydrodynamic drag calculations by the use of computer fluid
dynamic methods
Electronic states in quantum wires on the M\"{o}bius strip
In this work, we study the properties of an electron constrained on wires
along the M\"{o}bius strip. We considered wires around the strip and along the
transverse direction, across the width of the strip. For each direction, we
investigate how the curvature modifies the electronic states and their
corresponding energy spectrum. At the center of the strip, the wires around the
surface form quantum rings whose spectrum depends on the strip radius . For
wires at the edge of the strip, the inner edge turns into the outer edge.
Accordingly, the curvature yields localized states in the middle of the wire.
Along the strip width, the effective potential exhibits a parity symmetry
breaking leading to the localization of the bound state on one side of the
strip.Comment: 10 pages, 16 captioned figure
- …