20,908 research outputs found
Warm dark matter sterile neutrinos in electron capture and beta decay spectra
We briefly review the motivation to search for sterile neutrinos in the keV
mass scale, as dark matter candidates, and the prospects to find them in beta
decay or electron capture spectra, with a global perspective. We describe the
fundamentals of the neutrino flavor-mass eigenstate mismatch that opens the
possibility of detecting sterile neutrinos in such ordinary nuclear processes.
Results are shown and discussed for the effect of heavy neutrino emission in
electron capture in Holmium 163 and in two isotopes of Lead, 202 and 205, as
well as in the beta decay of Tritium. We study the de-excitation spectrum in
the considered cases of electron capture and the charged lepton spectrum in the
case of Tritium beta decay. For each of these cases, we define ratios of
integrated transition rates over different regions of the spectrum under study,
and give new results that may guide and facilitate the analysis of possible
future measurements, paying particular attention to forbidden transitions in
Lead isotopes.Comment: 13 pages, 4 figures, 2 table
Understanding the spiral structure of the Milky Way using the local kinematic groups
We study the spiral arm influence on the solar neighbourhood stellar
kinematics. As the nature of the Milky Way (MW) spiral arms is not completely
determined, we study two models: the Tight-Winding Approximation (TWA) model,
which represents a local approximation, and a model with self-consistent
material arms named PERLAS. This is a mass distribution with more abrupt
gravitational forces. We perform test particle simulations after tuning the two
models to the observational range for the MW spiral arm properties. We explore
the effects of the arm properties and find that a significant region of the
allowed parameter space favours the appearance of kinematic groups. The
velocity distribution is mostly sensitive to the relative spiral arm phase and
pattern speed. In all cases the arms induce strong kinematic imprints for
pattern speeds around 17 km/s/kpc (close to the 4:1 inner resonance) but no
substructure is induced close to corotation. The groups change significantly if
one moves only ~0.6 kpc in galactocentric radius, but ~2 kpc in azimuth. The
appearance time of each group is different, ranging from 0 to more than 1 Gyr.
Recent spiral arms can produce strong kinematic structures. The stellar
response to the two potential models is significantly different near the Sun,
both in density and kinematics. The PERLAS model triggers more substructure for
a larger range of pattern speed values. The kinematic groups can be used to
reduce the current uncertainty about the MW spiral structure and to test
whether this follows the TWA. However, groups such as the observed ones in the
solar vicinity can be reproduced by different parameter combinations. Data from
velocity distributions at larger distances are needed for a definitive
constraint.Comment: 18 pages, 21 figures, 4 tables; acccepted for publication in MNRA
Algebraic computation of some intersection D-modules
Let be a complex analytic manifold, a locally
quasi-homogeneous free divisor, an integrable logarithmic connection with
respect to and the local system of the horizontal sections of on
. In this paper we give an algebraic description in terms of of the
regular holonomic D-module whose de Rham complex is the intersection complex
associated with . As an application, we perform some effective computations
in the case of quasi-homogeneous plane curves.Comment: 18 page
A square root of the harmonic oscillator
Allowing for the inclusion of the parity operator, it is possible to
construct an oscillator model whose Hamiltonian admits an EXACT square root,
which is different from the conventional approach based on creation and
annihilation operators. We outline such a model, the method of solution and
some generalizations.Comment: RevTex, 10 pages in preprint form, no figure
Supersymmetry and superalgebra for the two-body system with a Dirac oscillator interaction
Some years ago, one of the authors~(MM) revived a concept to which he gave
the name of single-particle Dirac oscillator, while another~(CQ) showed that it
corresponds to a realization of supersymmetric quantum mechanics. The Dirac
oscillator in its one- and many-body versions has had a great number of
applications. Recently, it included the analytic expression for the eigenstates
and eigenvalues of a two-particle system with a new type of Dirac oscillator
interaction of frequency~. By considering the latter together with its
partner corresponding to the replacement of~ by~, we are able
to get a supersymmetric formulation of the problem and find the superalgebra
that explains its degeneracy.Comment: 21 pages, LaTeX, 1 figure (can be obtained from the authors), to
appear in J. Phys.
Experimental phase functions of mm-sized cosmic dust grains
We present experimental phase functions of three types of millimeter-sized
dust grains consisting of enstatite, quartz and volcanic material from Mount
Etna, respectively. The three grains present similar sizes but different
absorbing properties. The measurements are performed at 527 nm covering the
scattering angle range from 3 to 170 degrees. The measured phase functions show
two well defined regions i) soft forward peaks and ii) a continuous increase
with the scattering angle at side- and back-scattering regions. This behavior
at side- and back-scattering regions are in agreement with the observed phase
functions for the Fomalhaut and HR 4796A dust rings. Further computations and
measurements (including polarization) for millimeter sized-grains are needed to
draw some conclusions about the fluffy or compact structure of the dust grains
Charged-current inclusive neutrino cross sections in the SuperScaling model including quasielastic, pion production and meson-exchange contributions
Charged current inclusive neutrino-nucleus cross sections are evaluated using
the superscaling model for quasielastic scattering and its extension to the
pion production region. The contribution of two-particle-two-hole vector
meson-exchange current excitations is also considered within a fully
relativistic model tested against electron scattering data. The results are
compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE
experiments. For experiments where GeV, the
three mechanisms considered in this work provide good agreement with the data.
However, when the neutrino energy is larger, effects from beyond the
also appear to be playing a role. The results show that processes induced by
two-body currents play a minor role at the kinematics considered.Comment: 10 pages, 7 figure
Maximizing the hyperpolarizability of one-dimensional systems
Previous studies have used numerical methods to optimize the
hyperpolarizability of a one-dimensional quantum system. These studies were
used to suggest properties of one-dimensional organic molecules, such as the
degree of modulation of conjugation, that could potentially be adjusted to
improve the nonlinear-optical response. However, there were no conditions set
on the optimized potential energy function to ensure that the resulting
energies were consistent with what is observed in real molecules. Furthermore,
the system was placed into a one-dimensional box with infinite walls, forcing
the wavefunctions to vanish at the ends of the molecule. In the present work,
the walls are separated by a distance much larger than the molecule's length;
and, the variations of the potential energy function are restricted to levels
that are more typical of a real molecule. In addition to being a more
physically-reasonable model, our present approach better approximates the bound
states and approximates the continuum states - which are usually ignored. We
find that the same universal properties continue to be important for optimizing
the nonlinear-optical response, though the details of the wavefunctions differ
from previous result.Comment: 10 pages, 5 figure
Comprehensive study of Leon-Queretaro area
There are no author-identified significant results in this report
Childhood hypopigmented mycosis fungoides: a commonly delayed diagnosis
Primary cutaneous lymphomas (PCLs) are exceedingly rare in children and adolescents, with mycosis fungoides (MF) being the most frequent PCL diagnosed in childhood. There are numerous unusual clinical variants of MF, including the hypopigmented type form (HMF). HMF is exceptional overall, but comparatively common among children. We present an 8-year-old boy with a 3-year history of progressive, generalised, scaly, hypopigmented round patches and few erythematous papules. He was first diagnosed with pityriasis alba (PA), and moisturisers were prescribed with no improvement. Skin biopsy showed typical features of MF, and the patient was successfully treated with narrowband ultraviolet B. HMF may simulate atopic dermatitis, PA, pityriasis lichenoides, tinea versicolour, vitiligo, postinflammatory hypopigmentation or leprosy. Therefore, persistent and unusual hypopigmented lesions should be biopsied to rule out this rare variant of MF
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