269 research outputs found
Gravitational lensing by point masses on regular grid points
It is shown that gravitational lensing by point masses arranged in an
infinitely extended regular lattice can be studied analytically using the
Weierstrass functions. In particular, we draw the critical curves and the
caustic networks for the lenses arranged in regular-polygonal -- square,
equilateral triangle, regular hexagon -- grids. From this, the mean number of
positive parity images as a function of the average optical depth is derived
and compared to the case of the infinitely extended field of randomly
distributed lenses. We find that the high degree of the symmetry in the lattice
arrangement leads to a significant bias towards canceling of the shear caused
by the neighboring lenses on a given lens position and lensing behaviour that
is qualitatively distinct from the random star field. We also discuss some
possible connections to more realistic lensing scenarios.Comment: to appear in Monthly Notices of RAS, including 17 figs, 1 appendix.
High-res figs and F95 code used available upon reques
Human skeletal muscle nitrate store: influence of dietary nitrate supplementation and exercise
This is the final version. Available on open access from Wiley via the DOI in this recordRodent skeletal muscle contains a large store of nitrate that can be augmented by the consumption of dietary nitrate. This muscle nitrate reservoir has been found to be an important source of nitrite and nitric oxide (NO), via its reduction by tissue xanthine oxidoreductases (XOR). To explore if this pathway is also active in human skeletal muscle during exercise, and if it is sensitive to local nitrate availability, we assessed exercise-induced changes in muscle nitrate and nitrite concentrations in young healthy humans, under baseline conditions and following dietary nitrate consumption. We found that baseline nitrate and nitrite concentrations were far higher in muscle than in plasma (∼4-fold and ∼29-fold, respectively), and that the consumption of a single bolus of dietary nitrate (12.8 mmol) significantly elevated nitrate concentration in both plasma (∼19 fold) and muscle (∼5 fold). Consistent with these observations, and with previous suggestions of active muscle nitrate transport, we present Western blot data to show significant expression of the active nitrate/nitrite transporter, sialin, in human skeletal muscle. Furthermore, we report an exercise-induced reduction in human muscle nitrate concentration (by ∼39%), but only in the presence of an increased muscle nitrate store. Our results indicate that human skeletal muscle nitrate stores are sensitive to dietary nitrate intake and may contribute to NO generation during exercise. Together, these findings suggest that skeletal muscle plays an important role in the transport, storage and metabolism of nitrate in humans. This article is protected by copyright. All rights reserved
Reactor mixing angle from hybrid neutrino masses
In terms of its eigenvector decomposition, the neutrino mass matrix (in the
basis where the charged lepton mass matrix is diagonal) can be understood as
originating from a tribimaximal dominant structure with small deviations, as
demanded by data. If neutrino masses originate from at least two different
mechanisms, referred to as "hybrid neutrino masses", the experimentally
observed structure naturally emerges provided one mechanism accounts for the
dominant tribimaximal structure while the other is responsible for the
deviations. We demonstrate the feasibility of this picture in a fairly
model-independent way by using lepton-number-violating effective operators,
whose structure we assume becomes dictated by an underlying flavor
symmetry. We show that if a second mechanism is at work, the requirement of
generating a reactor angle within its experimental range always fixes the solar
and atmospheric angles in agreement with data, in contrast to the case where
the deviations are induced by next-to-leading order effective operators. We
prove this idea is viable by constructing an -based ultraviolet
completion, where the dominant tribimaximal structure arises from the type-I
seesaw while the subleading contribution is determined by either type-II or
type-III seesaw driven by a non-trivial singlet (minimal hybrid model).
After finding general criteria, we identify all the symmetries
capable of producing such -based minimal hybrid models.Comment: 18 pages, 5 figures. v3: section including sum rules added, accepted
by JHE
Detectability of Orbital Motion in Stellar Binary and Planetary Microlenses
A standard binary microlensing event lightcurve allows just two parameters of
the lensing system to be measured: the mass ratio of the companion to its host,
and the projected separation of the components in units of the Einstein radius.
However, other exotic effects can provide more information about the lensing
system. Orbital motion in the lens is one such effect, which if detected, can
be used to constrain the physical properties of the lens. To determine the
fraction of binary lens lightcurves affected by orbital motion (the detection
efficiency) we simulate lightcurves of orbiting binary star and star-planet
(planetary) lenses and simulate the continuous, high-cadence photometric
monitoring that will be conducted by the next generation of microlensing
surveys that are beginning to enter operation. The effect of orbital motion is
measured by fitting simulated lightcurve data with standard static binary
microlensing models; lightcurves that are poorly fit by these models are
considered to be detections of orbital motion. We correct for systematic false
positive detections by also fitting the lightcurves of static binary lenses.
For a continuous monitoring survey without intensive follow-up of high
magnification events, we find the orbital motion detection efficiency for
planetary events with caustic crossings to be 0.061+-0.010, consistent with
observational results, and 0.0130+-0.0055 for events without caustic crossings
(smooth events). Similarly for stellar binaries, the orbital motion detection
efficiency is 0.098+-0.011 for events with caustic crossings and is
0.048+-0.006 for smooth events. These result in combined (caustic crossing and
smooth) orbital motion detection efficiencies of 0.029+-0.005 for planetary
lenses and 0.070+-0.006 for stellar binary lenses. We also investigate how
various microlensing parameters affect the orbital motion detectability.
[Abridged]Comment: 21 pages, 22 figures, 5 table
Accidental stability of dark matter
We propose that dark matter is stable as a consequence of an accidental Z2
that results from a flavour-symmetry group which is the double-cover group of
the symmetry group of one of the regular geometric solids. Although
model-dependent, the phenomenology resembles that of a generic Higgs portal
dark matter scheme.Comment: 12 pages, final version, published in JHE
Optical Gravitational Lensing Experiment. OGLE-1999-BUL-19: The First Multi-Peak Parallax Event
We describe a highly unusual microlensing event, OGLE-1999-BUL-19, which
exhibits multiple peaks in its light curve. The Einstein radius crossing time
for this event is approximately one year, which is unusually long. We show that
the motion of the Earth induces these multiple peaks in the light curve, since
the relative transverse velocity of the lens projected into the observer plane
is very small (v = 12.5 km/s). This is the lowest velocity so far published and
we believe that this is the first multiple-peak parallax event ever observed.
We also believe that this event may be exhibiting slight binary-source
signatures in addition to these parallax-induced multiple peaks. With
spectroscopic observations it is possible to test this `parallax plus
binary-source' hypothesis and (if this hypothesis turns out to be correct) to
simultaneously fit both models and obtain a measurement of the lens mass.
Furthermore, spectroscopic observations could also supply information regarding
the lens properties, possibly providing another avenue for determining the lens
mass. We found that most of the I-band blending is probably caused by light
from the lens or a binary companion to the source. However, in the V-band,
there appears to be a second blended source 0.35" away from the lensed source.
HST observations will be very useful for understanding the nature of the
blends. We also suggest that a radial velocity survey of all parallax events
will be very useful for further constraining the lensing kinematics and
understanding the origins of these events and the excess of long events toward
the bulge.Comment: 36 pages, 7 figures. Accepted for publication in MNRA
The Cabibbo angle as a universal seed for quark and lepton mixings
A model-independent ansatz to describe lepton and quark mixing in a unified way is suggested based upon the Cabibbo angle. In our framework neutrinos mix in a ¿Bi-Large¿ fashion, while the charged leptons mix as the ¿down-type¿ quarks do. In addition to the standard Wolfenstein parameters (lambda, A) two other free parameters (psi, delta) are needed to specify the physical lepton mixing matrix. Through this simple assumption one makes specific predictions for the atmospheric angle as well as leptonic CP violation in good agreement with current observations
Asymmetric Inelastic Inert Doublet Dark Matter from Triplet Scalar Leptogenesis
The nature of dark matter (DM) particles and the mechanism that provides
their measured relic abundance are currently unknown. In this paper we
investigate inert scalar and vector like fermion doublet DM candidates with a
charge asymmetry in the dark sector, which is generated by the same mechanism
that provides the baryon asymmetry, namely baryogenesis-via-leptogenesis
induced by decays of scalar triplets. At the same time the model gives rise to
neutrino masses in the ballpark of oscillation experiments via type II seesaw.
We discuss possible sources of depletion of asymmetry in the DM and visible
sectors and solve the relevant Boltzmann equations for quasi-equilibrium decay
of triplet scalars. A Monte-Carlo-Markov-Chain analysis is performed for the
whole parameter space. The survival of the asymmetry in the dark sector leads
to inelastic scattering off nuclei. We then apply bayesian statistic to infer
the model parameters favoured by the current experimental data, in particular
the DAMA annual modulation and Xenon100 exclusion limit. The latter strongly
disfavours asymmetric scalar doublet DM of mass \mathcal{O}(\TeV) as required
by DM- oscillations, while an asymmetric vector like fermion
doublet DM with mass around 100 GeV is a good candidate for DAMA annual
modulation yet satisfying the constraints from Xenon100 data.Comment: 35 pages and 15 figures, references adde
Observables in Neutrino Mass Spectroscopy Using Atoms
The process of collective de-excitation of atoms in a metastable level into emission mode of a single photon plus a neutrino pair, called radiative emission of neutrino pair (RENP), is sensitive to the absolute neutrino mass scale, to the neutrino mass hierarchy and to the nature (Dirac or Majorana) of massive neutrinos. We investigate how the indicated neutrino mass and mixing observables can be determined from the measurement of the corresponding continuous photon spectrum taking the example of a transition between specific levels of the Yb atom. The possibility of determining the nature of massive neutrinos and, if neutrinos are Majorana fermions, of obtaining information about the Majorana phases in the neutrino mixing matrix, is analyzed in the cases of normal hierarchical, inverted hierarchical and quasi-degenerate types of neutrino mass spectrum. We find, in particular, that the sensitivity to the nature of massive neutrinos depends critically on the atomic level energy difference relevant in the RENP. \ua9 2013 Elsevier B.V
Relating quarks and leptons with the T-7 flavour group
In this letter we present a model for quarks and leptons based on T-7 as flavour symmetry, predicting a canonical mass relation between charged leptons and down-type quarks proposed earlier. Neutrino masses are generated through a Type-I seesaw mechanism, with predicted correlations between the atmospheric mixing angle and neutrino masses. Compatibility with oscillation results leads to lower bounds for the lightest neutrino mass as well as for the neutrinoless double beta decay rates, even for normal neutrino mass hierarchy
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