29,233 research outputs found
Are small neutrino masses unveiling the missing mass problem of the Universe?
We present a scenario in which a remarkably simple relation linking dark
matter properties and neutrino masses naturally emerges. This framework points
towards a low energy theory where the neutrino mass originates from the
existence of a light scalar dark matter particle in the MeV mass range. A very
surprising aspect of this scenario is that the required MeV dark matter is one
of the favoured candidates to explain the mysterious emission of 511 keV
photons in the centre of our galaxy. A possible interpretation of these
findings is that dark matter is the stepping stone of a theory beyond the
standard model instead of being an embarrassing relic whose energy density must
be accounted for in any successful model building.Comment: 4pages, 2 figures. Two paragraphs have been added. One for the
complex case; the other one for the UV completio
Short-Baseline Active-Sterile Neutrino Oscillations?
We suggest the possibility that the anomalies observed in the LSND experiment
and the Gallium radioactive source experiments may be due to neutrino
oscillations generated by a large squared-mass difference of about 20 - 30
eV^2. We consider the simplest 3+1 four-neutrino scheme that can accommodate
also the observed solar and atmospheric neutrino oscillations. We show that, in
this framework, the disappearance of nu_e and nu_mu in short-baseline neutrino
oscillation experiments is mainly due to active-sterile transitions. The
implications of the first MiniBooNE results, appeared after the completion of
this paper, are discussed in an addendum.Comment: 12 pages. The implications of the first MiniBooNE results are
discussed in an addendu
Tycho Brahe's supernova: light from centuries past
The light curve of SN 1572 is described in the terms used nowadays to
characterize SNeIa. By assembling the records of the observations done in
1572--74 and evaluating their uncertainties, it is possible to recover the
light curve and the color evolution of this supernova. It is found that, within
the SNe Ia family, the event should have been a SNIa with a normal rate of
decline, its stretch factor being {\it s} 0.9. Visual light curve near
maximum, late--time decline and the color evolution sustain this conclusion.
After correcting for extinction, the luminosity of this supernova is found to
be M --19.58 --5 log (D/3.5 kpc) 0.42.Comment: 28 pages, 3 figures, 3 tables. submitted to ApJ (Main Journal
High-pressure structural investigation of several zircon-type orthovanadates
Room temperature angle-dispersive x-ray diffraction measurements on
zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three
compounds we found evidence of a pressure-induced structural phase
transformation from zircon to a scheelite-type structure. The onset of the
transition is near 8 GPa, but the transition is sluggish and the low- and
high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and
LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa.
The equations of state for the zircon and scheelite phases are also determined.
Among the three studied compounds, we found that ScVO4 is less compressible
than EuVO4 and LuVO4, being the most incompressible orthovanadate studied to
date. The sequence of structural transitions and compressibilities are
discussed in comparison with other zircon-type oxides.Comment: 34 pages, 2 Tables, 11 Figure
Features of the Extension of a Statistical Measure of Complexity to Continuous Systems
We discuss some aspects of the extension to continuous systems of a
statistical measure of complexity introduced by Lopez-Ruiz, Mancini and Calbet
(LMC) [Phys. Lett. A 209 (1995) 321]. In general, the extension of a magnitude
from the discrete to the continuous case is not a trivial process and requires
some choice. In the present study, several possibilities appear available. One
of them is examined in detail. Some interesting properties desirable for any
magnitude of complexity are discovered on this particular extension.Comment: 22 pages, 0 figure
Inhomogeneous turbulence in the vicinity of a large scale coherent vortex
We study the statistics of turbulent velocity fluctuations in the
neighbourhood of a strong large scale vortex at very large Reynolds number. At
each distance from the vortex core, we observe that the velocity spectrum has a
power law ``inertial range'' of scales and that intermittency -- defined as the
variation of the probability density function (PDF) of velocity increments as
the length of the increment is varied -- is also present. We show that the
spectrum scaling exponents and intermittency characteristics vary with the
distance to the vortex. They are also influenced by the large scale dynamics of
the vortex.Comment: submitted to europhys lett, 6 pages, 5 figure
D-branes with Lorentzian signature in the Nappi-Witten model
Lorentzian signature D-branes of all dimensions for the Nappi-Witten string
are constructed. This is done by rewriting the gluing condition for
the model chiral currents on the brane as a well posed first order differential
problem and by solving it for Lie algebra isometries other than Lie algebra
automorphisms. By construction, these D-branes are not twined conjugacy
classes. Metrically degenerate D-branes are also obtained.Comment: 22 page
- âŠ