3,913 research outputs found
Wormholes and masses for Goldstone bosons
There exist non-trivial stationary points of the Euclidean action for an
axion particle minimally coupled to Einstein gravity, dubbed wormholes. They
explicitly break the continuos global shift symmetry of the axion in a
non-perturbative way, and generate an effective potential that may compete with
QCD depending on the value of the axion decay constant. In this paper, we
explore both theoretical and phenomenological aspects of this issue. On the
theory side, we address the problem of stability of the wormhole solutions, and
we show that the spectrum of the quadratic action features only positive
eigenvalues. On the phenomenological side, we discuss, beside the obvious
application to the QCD axion, relevant consequences for models with ultralight
dark matter, black hole superradiance, and the relaxation of the electroweak
scale. We conclude discussing wormhole solutions for a generic coset and the
potential they generate.Comment: 50 pages, 15 figures. v2: minor changes, refs adde
Chaotic Vibrations in a Buckled Beam Induced by a Galloping Phenomenon
Chaos theory has spectacularly evolved since the pioneering work by E. Lorenz on chaotic motion in a simple, deterministic system. Since then, the chaotic behavior of many other deterministic, low-dimensional systems in a large variety of fields has been developed. In the particular field of aeroelasticity of aircraft structures several reports of chaos have been documented. However, we are unaware of any report of chaotic systems of civil (non-aeronautical) use induced by an aeroelastic phenomenon. In this paper a well defined civil, aeroelastic system, susceptible to exhibit chaotic behavior is presented. The system consists of a buckled beam from which a second beam is suspended. This last beam (hereafter, galloping beam) has a square cross- section and can undergo transverse galloping. The system is subjected to an uniform wind flow and, as it will be shown in the paper, for wind velocities larger than a threshold value, the galloping beam begins to oscillate and induces, for a determined set of parameter values, a chaotic motion in the buckled bea
The potential of leptonic minimal flavour violation
We explore the possibility of spontaneous lepton flavour symmetry breaking in the context of Minimal Flavour Violation and within a minimal and predictive See-Saw model. In this context the Yukawa couplings are the vacuum expectation values of scalar fields transforming under the flavour group. The scalar potential giving rise to the acquisition of the vev of the scalar fields is derived and analyzed. In the minimization the Majorana character of neutrino masses plays a distinctive role, absent for the quark caseR. A. acknowledge partial support from the European Union FP7 ITN INVISIBLES (Marie Curie Actions,PITN- GA-2011- 289442), CiCYT support through the project FPA2009-09017, CAM partial support through the project HEPHACOS P-ESP-00346 and MICINN support through the grant BES-2010-03786
Lorenz-Mie scattering of focused light via complex focus fields: an analytic treatment
The Lorenz-Mie scattering of a wide class of focused electromagnetic fields
off spherical particles is studied. The focused fields in question are
constructed through complex focal displacements, leading to closed-form
expressions that can exhibit several interesting physical properties, such as
orbital and/or spin angular momentum, spatially-varying polarization, and a
controllable degree of focusing. These fields constitute complete bases that
can be considered as nonparaxial extensions of the standard Laguerre-Gauss
beams and the recently proposed polynomials-of-Gaussians beams. Their analytic
form turns out to lead also to closed-form expressions for their multipolar
expansion. Such expansion can be used to compute the field scattered by a
spherical particle and the resulting forces and torques exerted on it, for any
relative position between the field's focus and the particle.Comment: 11 pages, 7 figure
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