33,013 research outputs found
On Duffin-Kemmer-Petiau particles with a mixed minimal-nonminimal vector coupling and the nondegenerate bound states for the one-dimensional inversely linear background
The problem of spin-0 and spin-1 bosons in the background of a general mixing
of minimal and nonminimal vector inversely linear potentials is explored in a
unified way in the context of the Duffin-Kemmer-Petiau theory. It is shown that
spin-0 and spin-1 bosons behave effectively in the same way. An orthogonality
criterion is set up and it is used to determine uniquely the set of solutions
as well as to show that even-parity solutions do not exist.Comment: 10 page
Bound states of bosons and fermions in a mixed vector-scalar coupling with unequal shapes for the potentials
The Klein-Gordon and the Dirac equations with vector and scalar potentials
are investigated under a more general condition, . These intrinsically relativistic and isospectral problems
are solved in a case of squared hyperbolic potential functions and bound states
for either particles or antiparticles are found. The eigenvalues and
eigenfuntions are discussed in some detail and the effective Compton wavelength
is revealed to be an important physical quantity. It is revealed that a boson
is better localized than a fermion when they have the same mass and are
subjected to the same potentials.Comment: 3 figure
The peremptory influence of a uniform background for trapping neutral fermions with an inversely linear potential
The problem of neutral fermions subject to an inversely linear potential is
revisited. It is shown that an infinite set of bound-state solutions can be
found on the condition that the fermion is embedded in an additional uniform
background potential. An apparent paradox concerning the uncertainty principle
is solved by introducing the concept of effective Compton wavelength
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Charge-fluctuation contribution to the Raman response in superconducting cuprates
We calculate the Raman response contribution due to collective modes, finding
a strong dependence on the photon polarizations and on the characteristic
wavevectors of the modes. We compare our results with recent Raman spectroscopy
experiments in underdoped cuprates, and
, where anomalous low-energy peaks are
observed, which soften upon lowering the temperature. We show that the specific
dependence on doping and on photon polarizations of these peaks is only
compatible with charge collective excitations at finite wavelength.Comment: 5 pages, 3 figure
Fermion localization on branes with generalized dynamics
In this letter we consider a specific model of braneworld with nonstandard
dynamics diffused in the literature, specifically we focus our attention on the
matter energy density, the energy of system, the Ricci scalar and the thin
brane limit. As the model is classically stable and capable of localize
gravity, as a natural extension we address the issue of fermion localization of
fermions on a thick brane constructed out from one scalar field with
nonstandard kinetic terms coupled with gravity. The contribution of the
nonstandard kinetic terms in the problem of fermion localization is analyzed.
It is found that the simplest Yukawa coupling support
the localization of fermions on the thick brane. It is shown that the zero mode
for left-handed can be localized on the thick brane depending on the values for
the coupling constant .Comment: 6 pages, 3 figure
Pinning of a two-dimensional membrane on top of a patterned substrate: the case of graphene
We study the pinning of a two-dimensional membrane to a patterned substrate
within elastic theory both in the bending rigidity and in the strain dominated
regimes. We find that both the in-plane strains and the bending rigidity can
lead to depinning. We show from energetic arguments that the system experiences
a first order phase transition between the attached configuration to a
partially detached one when the relevant parameters of the substrate are
varied, and we construct a qualitative phase diagram. Our results are confirmed
through analytical solutions for some simple geometries of the substrate's
profile.Comment: Minor changes. Final version, as publishe
Observation of the Kohn anomaly near the K point of bilayer graphene
The dispersion of electrons and phonons near the K point of bilayer graphene
was investigated in a resonant Raman study using different laser excitation
energies in the near infrared and visible range. The electronic structure was
analyzed within the tight-binding approximation, and the
Slonczewski-Weiss-McClure (SWM) parameters were obtained from the analysis of
the dispersive behavior of the Raman features. A softening of the phonon
branches was observed near the K point, and results evidence the Kohn anomaly
and the importance of considering electron-phonon and electron-electron
interactions to correctly describe the phonon dispersion in graphene systems.Comment: 4 pages, 4 figure
Multi-objective evolutionary–fuzzy augmented flight control for an F16 aircraft
In this article, the multi-objective design of a fuzzy logic augmented flight controller for a high performance fighter jet (the Lockheed-Martin F16) is described. A fuzzy logic controller is designed and its membership functions tuned by genetic algorithms in order to design a roll, pitch, and yaw flight controller with enhanced manoeuverability which still retains safety critical operation when combined with a standard inner-loop stabilizing controller. The controller is assessed in terms of pilot effort and thus reduction of pilot fatigue. The controller is incorporated into a six degree of freedom motion base real-time flight simulator, and flight tested by a qualified pilot instructor
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