44,158 research outputs found
Texture-zero model for the lepton mass matrices
We suggest a simple model, based on the type-I seesaw mechanism, for the
lepton mass matrices. The model hinges on an Abelian symmetry which leads to
mass matrices with some vanishing matrix elements. The model predicts one
massless neutrino and ( is the effective light-neutrino
Majorana mass matrix). We show that these predictions perfectly agree with the
present experimental data if the neutrino mass spectrum is inverted, i.e. if
, provided the Dirac phase is very close to maximal (). In the case of a normal neutrino mass spectrum, i.e. when , the
agreement of our model with the data is less than optimal---the reactor mixing
angle is too small in our model. Minimal leptogenesis is not an
option in our model due to the vanishing elements in the Yukawa-coupling
matrices.Comment: 10 pages, 3 figures; version for journal: new fit to data, new plot
New textures for the lepton mass matrices
We study predictive textures for the lepton mass matrices in which the
charged-lepton mass matrix has either four or five zero matrix elements while
the neutrino Majorana mass matrix has, respectively, either four or three zero
matrix elements. We find that all the viable textures of these two kinds share
many predictions: the neutrino mass spectrum is inverted, the sum of the
light-neutrino masses is close to 0.1 eV, the Dirac phase in the
lepton mixing matrix is close to either or , and the mass term
responsible for neutrinoless double-beta decay lies in between 12 and 22 meV.Comment: 31 pages, 6 figure
Spatially resolved physical and chemical properties of the planetary nebula NGC 3242
Optical integral-field spectroscopy was used to investigate the planetary
nebula NGC 3242. We analysed the main morphological components of this source,
including its knots, but not the halo. In addition to revealing the properties
ofthe physical and chemical nature of this nebula, we also provided reliable
spatially resolved constraints that can be used for future photoionisation
modelling of the nebula. The latter is ultimately necessary to obtain a fully
self-consistent 3D picture of the physical and chemical properties of the
object. The observations were obtained with the VIMOS instrument attached to
VLT-UT3. Maps and values for specific morphological zones for the detected
emission-lines were obtained and analysed with routines developed by the
authors to derive physical and chemical conditions of the ionised gas in a 2D
fashion. We obtained spatially resolved maps and mean values of the electron
densities, temperatures, and chemical abundances, for specific morphological
structures in NGC 3242. These results show the pixel-to-pixel variations of the
the small- and large-scale structures of the source. These diagnostic maps
provide information free from the biases introduced by traditional single
long-slit observations. In general, our results are consistent with a uniform
abundance distribution for the object, whether we look at abundance maps or
integrated fluxes from specified morphological structures. The results indicate
that special care should be taken with the calibration of the data and that
only data with extremely good signal-to-noise ratio and spectral coverage
should be used to ensure the detection of possible spatial variations.Comment: 11 pages, 8 figures accepted for publication in Astronomy &
Astrophysic
First- and second-order phase transitions in Ising models on small world networks, simulations and comparison with an effective field theory
We perform simulations of random Ising models defined over small-world
networks and we check the validity and the level of approximation of a recently
proposed effective field theory. Simulations confirm a rich scenario with the
presence of multicritical points with first- or second-order phase transitions.
In particular, for second-order phase transitions, independent of the dimension
d_0 of the underlying lattice, the exact predictions of the theory in the
paramagnetic regions, such as the location of critical surfaces and correlation
functions, are verified. Quite interestingly, we verify that the
Edwards-Anderson model with d_0=2 is not thermodynamically stable under graph
noise.Comment: 12 pages, 12 figures, 1 tabl
Flavour symmetries in a renormalizable SO(10) model
In the context of a renormalizable supersymmetric SO(10) Grand Unified
Theory, we consider the fermion mass matrices generated by the Yukawa couplings
to a representation
of scalars. We perform a complete investigation of the possibilities of
imposing flavour symmetries in this scenario; the purpose is to reduce the
number of Yukawa coupling constants in order to identify potentially predictive
models. We have found that there are only 14 inequivalent cases of Yukawa
coupling matrices, out of which 13 cases are generated by symmetries,
with suitable , and one case is generated by a symmetry. A
numerical analysis of the 14 cases reveals that only two of them---dubbed A and
B in the present paper---allow good fits to the experimentally known fermion
masses and mixings.Comment: 36 pages, no figures, revised fits using newer data, added fit for
case A, added references, new appendices concerning the SO(10) scalar
potential and inequalities for the vacuum expectation values, conclusions
unchanged; some minor changes, matches published versio
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