1,458 research outputs found
Remaining inconsistencies with solar neutrinos: can spin flavour precession provide a clue?
A few inconsistencies remain after it has been ascertained that LMA is the
dominant solution to the solar neutrino problem: why is the SuperKamiokande
spectrum flat and why is the Chlorine rate prediction over two standard
deviations above the data. There also remains the ananswered and important
question of whether the active neutrino flux is constant or time varying. We
propose a scenario involving spin flavour precession to sterile neutrinos with
three active flavours that predicts a flat SuperK spectrum and a Chlorine rate
prediction more consistent with data. We also argue that running the Borexino
experiment during the next few years may provide a very important clue as to
the possible variability of the solar neutrino flux.Comment: 3 pages, 2 figures, contribution to TAUP 2009 (Rome
Actin- and myosin-dependent vesicle loading of presynaptic docking sites prior to exocytosis.
Variance analysis of postsynaptic current amplitudes suggests the presence of distinct docking sites (also called release sites) where vesicles pause before exocytosis. Docked vesicles participate in the readily releasable pool (RRP), but the relation between docking site number and RRP size remains unclear. It is also unclear whether all vesicles of the RRP are equally release competent, and what cellular mechanisms underlie RRP renewal. We address here these questions at single glutamatergic synapses, counting released vesicles using deconvolution. We find a remarkably low variance of cumulative vesicle counts during action potential trains. This, combined with Monte Carlo simulations, indicates that vesicles transit through two successive states before exocytosis, so that the RRP is up to 2-fold higher than the docking site number. The transition to the second state has a very rapid rate constant, and is specifically inhibited by latrunculin B and blebbistatin, suggesting the involvement of actin and myosin
ASTROD and ASTROD I -- Overview and Progress
In this paper, we present an overview of ASTROD (Astrodynamical Space Test of
Relativity using Optical Devices) and ASTROD I mission concepts and studies.
The missions employ deep-space laser ranging using drag-free spacecraft to map
the gravitational field in the solar-system. The solar-system gravitational
field is determined by three factors: the dynamic distribution of matter in the
solar system; the dynamic distribution of matter outside the solar system
(galactic, cosmological, etc.) and gravitational waves propagating through the
solar system. Different relativistic theories of gravity make different
predictions of the solar-system gravitational field. Hence, precise
measurements of the solar-system gravitational field test all these. The tests
and observations include: (i) a precise determination of the relativistic
parameters beta and gamma with 3-5 orders of magnitude improvement over
previous measurements; (ii) a 1-2 order of magnitude improvement in the
measurement of G-dot; (iii) a precise determination of any anomalous, constant
acceleration Aa directed towards the Sun; (iv) a measurement of solar angular
momentum via the Lense-Thirring effect; (v) the detection of solar g-mode
oscillations via their changing gravity field, thus, providing a new eye to see
inside the Sun; (vi) precise determination of the planetary orbit elements and
masses; (viii) better determination of the orbits and masses of major
asteroids; (ix) detection and observation of gravitational waves from massive
black holes and galactic binary stars in the frequency range 0.05 mHz to 5 mHz;
and (x) exploring background gravitational-waves.Comment: 17 pages, 6 figures, presented to The Third International ASTROD
Symposium on Laser Astrodynamics, Space Test of Relativity and
Gravitational-Wave Astronomy, Beijing, July 14-16, 2006; International
Journal of Modern Physics D, in press (2008
Multi-wavelength study of the low-luminosity outbursting young star HBC 722
HBC 722 (V2493 Cyg) is a young eruptive star in outburst since 2010. It is an
FU Orionis-type object with an atypically low outburst luminosity. Because it
was well characterized in the pre-outburst phase, HBC 722 is one of the few
FUors where we can learn about the physical changes and processes associated
with the eruption. We monitored the source in the BVRIJHKs bands from the
ground, and at 3.6 and 4.5 m from space with the Spitzer Space Telescope.
We analyzed the light curves and the spectral energy distribution by fitting a
series of steady accretion disk models at many epochs. We also analyzed the
spectral properties of the source based on new optical and infrared spectra. We
also mapped HBC 722 and its surroundings at millimeter wavelengths. From the
light curve analysis we concluded that the first peak of the outburst in 2010
September was due to an abrupt increase of the accretion rate in the innermost
part of the system. This was followed by a long term process, when the
brightening was mainly due to a gradual increase of the accretion rate and the
emitting area. Our new observations show that the source is currently in a
constant plateau phase. We found that around the peak the continuum was bluer
and the H profile changed significantly between 2012 and 2013. The
source was not detected in the millimeter continuum, but we discovered a
flattened molecular gas structure with a diameter of 1700 au and mass of 0.3
M centered on HBC 722. While the first brightness peak could be
interpreted as a rapid fall of piled-up material from the inner disk onto the
star, the later monotonic flux rise suggests the outward expansion of a hot
component according to the theory of Bell & Lin (1994). Our study of HBC 722
demonstrated that accretion-related outbursts can occur in young stellar
objects even with very low mass disks, in the late Class II phase.Comment: 11 pages, 7 figures, 3 online tables. Accepted for publication in the
A&
Non-equilibrium entangled steady state of two independent two-level systems
We determine and study the steady state of two independent two-level systems
weakly coupled to a stationary non-equilibrium environment. Whereas this
bipartite state is necessarily uncorrelated if the splitting energies of the
two-level systems are different from each other, it can be entangled if they
are equal. For identical two-level systems interacting with two bosonic heat
baths at different temperatures, we discuss the influence of the baths
temperatures and coupling parameters on their entanglement. Geometric
properties, such as the baths dimensionalities and the distance between the
two-level systems, are relevant. A regime is found where the steady state is a
statistical mixture of the product ground state and of the entangled singlet
state with respective weights 2/3 and 1/3
Solar System Objects in the ISOPHOT 170 micron Serendipity Survey
The ISOPHOT Serendipity Survey (ISOSS) covered approximately 15 % of the sky
at a wavelength of 170 micron while the ISO satellite was slewing from one
target to the next. By chance ISOSS slews went over many solar system objects
(SSOs). We identified the comets, asteroids and planets in the slews through a
fast and effective search procedure based on N-body ephemeris and flux
estimates. The detections were analysed from a calibration and scientific point
of view. Through the measurements of the well-known asteroids Ceres, Pallas,
Juno and Vesta and the planets Uranus and Neptune it was possible to improve
the photometric calibration of ISOSS and to extend it to higher flux regimes.
We were also able to establish calibration schemes for the important slew end
data. For the other asteroids we derived radiometric diameters and albedos
through a recent thermophysical model. The scientific results are discussed in
the context of our current knowledge of size, shape and albedos, derived from
IRAS observations, occultation measurements and lightcurve inversion
techniques. In all cases where IRAS observations were available we confirm the
derived diameters and albedos. For the five asteroids without IRAS detections
only one was clearly detected and the radiometric results agreed with sizes
given by occultation and HST observations. Four different comets have clearly
been detected at 170 micron and two have marginal detections. The observational
results are presented to be used by thermal comet models in the future. The
nine ISOSS slews over Hale-Bopp revealed extended and asymmetric structures
related to the dust tail. We attribute the enhanced emission in post-perihelion
observations to large particles around the nucleus. The signal patterns are
indicative of a concentration of the particles in trail direction.Comment: 15 pages, 6 figures, 6 tables; Accepted for publication in Astronomy
and Astrophysic
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Three-generation study of neutrino spin-flavor conversion in supernova and implication for neutrino magnetic moment
We investigate resonant spin-flavor (RSF) conversions of supernova neutrinos
which are induced by the interaction of neutrino magnetic moment and supernova
magnetic fields. From the formulation which includes all three-flavor neutrinos
and anti-neutrinos, we give a new crossing diagram that includes not only
ordinary MSW resonance but also magnetically-induced RSF effect. With the
diagram, it is found that four conversions occur in supernova, two are induced
by the RSF effect and two by the pure MSW. We also numerically calculate
neutrino conversions in supernova matter, using neutrino mixing parameters
inferred from recent experimental results and a realistic supernova progenitor
model. The results indicate that until 0.5 seconds after core bounce, the
RSF-induced transition occurs
efficiently (adiabatic resonance), when \mu_\nu \agt 10^{-12} \mu_B
(B_0 / 5 \times 10^{9} \mathrm G)^{-1}, where is the strength of the
magnetic field at the surface of iron core. We also evaluate the energy
spectrum as a function of at the SuperKamiokande detector and the
Sudbury Neutrino Observatory using the calculated conversion probabilities, and
find that the spectral deformation might have possibility to provide useful
information on neutrino magnetic moment as well as magnetic field strength in
supernovae.Comment: 35 pages, 13 figure
Exploring the circumstellar environment of the young eruptive star V2492 Cyg
Context. V2492 Cyg is a young eruptive star that went into outburst in 2010.
The near-infrared color changes observed since the outburst peak suggest that
the source belongs to a newly defined sub-class of young eruptive stars, where
time-dependent accretion and variable line-of-sight extinction play a combined
role in the flux changes.
Aims. In order to learn about the origin of the light variations and to
explore the circumstellar and interstellar environment of V2492 Cyg, we
monitored the source at ten different wavelengths, between 0.55 \mu m and 2.2
\mu m from the ground and between 3.6 \mu m and 160 \mu m from space.
Methods. We analyze the light curves and study the color-color diagrams via
comparison with the standard reddening path. We examine the structure of the
molecular cloud hosting V2492 Cyg by computing temperature and optical depth
maps from the far-infrared data.
Results. We find that the shapes of the light curves at different wavelengths
are strictly self-similar and that the observed variability is related to a
single physical process, most likely variable extinction. We suggest that the
central source is episodically occulted by a dense dust cloud in the inner
disk, and, based on the invariability of the far-infrared fluxes, we propose
that it is a long-lived rather than a transient structure. In some respects,
V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars.
Conclusions. The example of V2492 Cyg demonstrates that the light variations
of young eruptive stars are not exclusively related to changing accretion. The
variability provided information on an azimuthally asymmetric structural
element in the inner disk. Such an asymmetric density distribution in the
terrestrial zone may also have consequences for the initial conditions of
planet formation.Comment: 9 pages, 7 figures, 2 online tables, accepted for publication in A&
Bounds on the tau and muon neutrino vector and axial vector charge radius
A Majorana neutrino is characterized by just one flavor diagonal
electromagnetic form factor: the anapole moment, that in the static limit
corresponds to the axial vector charge radius . Experimental information
on this quantity is scarce, especially in the case of the tau neutrino. We
present a comprehensive analysis of the available data on the single photon
production process off Z-resonance, and we
discuss the constraints that these measurements can set on for the tau
neutrino. We also derive limits for the Dirac case, when the presence of a
vector charge radius is allowed. Finally, we comment on additional
experimental data on scattering from the NuTeV, E734, CCFR and
CHARM-II collaborations, and estimate the limits implied for and
for the muon neutrino.Comment: 20 pages, 2 eps figures. CCFR data included in the analysis.
Conclusion unchange
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