11,014 research outputs found
Quantum Hamiltonians with Quasi-Ballistic Dynamics and Point Spectrum
Consider the family of Schr\"odinger operators (and also its Dirac version)
on or where is a
transformation on (compact metric) , a real Lipschitz function and
a (sufficiently fast) power-decaying perturbation. Under certain conditions
it is shown that presents quasi-ballistic dynamics for
in a dense set. Applications include potentials generated
by rotations of the torus with analytic condition on , doubling map, Axiom A
dynamical systems and the Anderson model. If is a rank one perturbation,
examples of with quasi-ballistic dynamics and point spectrum
are also presented.Comment: 17 pages; to appear in Journal of Differential Equation
Dynamical Delocalization for the 1D Bernoulli Discrete Dirac Operator
An 1D tight-binding version of the Dirac equation is considered; after
checking that it recovers the usual discrete Schr?odinger equation in the
nonrelativistic limit, it is found that for two-valued Bernoulli potentials the
zero mass case presents absence of dynamical localization for specific values
of the energy, albeit it has no continuous spectrum. For the other energy
values (again excluding some very specific ones) the Bernoulli Dirac system is
localized, independently of the mass.Comment: 9 pages, no figures - J. Physics A: Math. Ge
Dynamical Lower Bounds for 1D Dirac Operators
Quantum dynamical lower bounds for continuous and discrete one-dimensional
Dirac operators are established in terms of transfer matrices. Then such
results are applied to various models, including the Bernoulli-Dirac one and,
in contrast to the discrete case, critical energies are also found for the
continuous Dirac case with positive mass.Comment: 18 pages; to appear in Math.
Stable retrograde orbits around the triple system 2001 SN263
The NEA 2001 SN263 is the target of the ASTER MISSION - First Brazilian Deep
Space Mission. Araujo et al. (2012), characterized the stable regions around
the components of the triple system for the planar and prograde cases. Knowing
that the retrograde orbits are expected to be more stable, here we present a
complementary study. We now considered particles orbiting the components of the
system, in the internal and external regions, with relative inclinations
between , i.e., particles with retrograde
orbits. Our goal is to characterize the stable regions of the system for
retrograde orbits, and then detach a preferred region to place the space probe.
For a space mission, the most interesting regions would be those that are
unstable for the prograde cases, but stable for the retrograde cases. Such
configuration provide a stable region to place the mission probe with a
relative retrograde orbit, and, at the same time, guarantees a region free of
debris since they are expected to have prograde orbits. We found that in fact
the internal and external stable regions significantly increase when compared
to the prograde case. For particles with and , we found
that nearly the whole region around Alpha and Beta remain stable. We then
identified three internal regions and one external region that are very
interesting to place the space probe. We present the stable regions found for
the retrograde case and a discussion on those preferred regions. We also
discuss the effects of resonances of the particles with Beta and Gamma, and the
role of the Kozai mechanism in this scenario. These results help us understand
and characterize the stability of the triple system 2001 SN263 when retrograde
orbits are considered, and provide important parameters to the design of the
ASTER mission.Comment: 11 pages, 8 figures. Accepted for publication in MNRAS - 2015 March
1
Graviton-photon oscillation in alternative theories of gravity
In this paper we investigate graviton-photon oscillation in the presence of
an external magnetic field in alternative theories of gravity. Whereas the
effect of an effective refractive index for the electromagnetic radiation was
already considered in the literature, we develop the first approach to take
into account the effect of the modification of the predictions for
gravitational waves in alternative theories of gravity in the phenomenon of
graviton-photon mixing.Comment: V1: 5 pages. V2: 9 pages (new style); clarifications in the
discussion included, no physics changes; 3 references added. V3: 10 pages, 4
references added, discussion extended. Version accepted for publication in
Classical and Quantum Gravit
The role of short periodic orbits in quantum maps with continuous openings
We apply a recently developed semiclassical theory of short periodic orbits
to the continuously open quantum tribaker map. In this paradigmatic system the
trajectories are partially bounced back according to continuous reflectivity
functions. This is relevant in many situations that include optical
microresonators and more complicated boundary conditions. In a perturbative
regime, the shortest periodic orbits belonging to the classical repeller of the
open map - a cantor set given by a region of exactly zero reflectivity - prove
to be extremely robust in supporting a set of long-lived resonances of the
continuously open quantum maps. Moreover, for step like functions a significant
reduction in the number needed is obtained, similarly to the completely open
situation. This happens despite a strong change in the spectral properties when
compared to the discontinuous reflectivity case.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1604.0181
GIS as a tool for balanced fertilization and sustainable development of agriculture in the savannas of South America.
Stability in quadratic torsion theories
We revisit the definition and some of the characteristics of quadratic
theories of gravity with torsion. We start from the most general Lagrangian
density quadratic in the curvature and torsion tensors. By assuming that
General Relativity should be recovered when torsion vanishes and investigating
the behaviour of the vector and pseudovector torsion fields in the weak-gravity
regime, we present a set of necessary conditions for the stability of these
theories. Moreover, we explicitly obtain the gravitational field equations
using the Palatini variational principle with the metricity condition
implemented via a Lagrange multiplier
Impact of DM direct searches and the LHC analyses on branon phenomenology
Dark Matter direct detection experiments are able to exclude interesting
parameter space regions of particle models which predict an important amount of
thermal relics. We use recent data to constrain the branon model and to compute
the region that is favored by CDMS measurements. Within this work, we also
update present colliders constraints with new studies coming from the LHC.
Despite the present low luminosity, it is remarkable that for heavy branons,
CMS and ATLAS measurements are already more constraining than previous analyses
performed with TEVATRON and LEP data.Comment: 17 pages, 2 figure
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