1,073 research outputs found
Interactions of the solar neutrinos with the deuterons
Starting from chiral Lagrangians, possessing the SU(2)_L x SU(2)_R local
chiral symmetry, we derive weak axial one-boson exchange currents in the
leading order in the 1/M expansion (M is the nucleon mass). We apply these
currents in calculations of the cross sections for the disintegration of the
deuterons by the low energy neutrinos. The nuclear wave functions are derived
from a variant of the OBEPQB potential and from the Nijmegen 93 and Nijmegen I
nucleon-nucleon interactions. The comparison of our cross sections with those
obtained within the pionless effective field theory and other potential model
calculations shows that the solar neutrino-deuteron cross sections can be
calculated within an accuracy of 3.3 %.Comment: 6 pages, 1 figure, 6 tables, conference tal
Model dependence of the neutrino-deuteron disintegration cross sections at low energies
Model dependence of the reaction rates for the weak breakup of deuterons by
low energy neutrinos is studied starting from the cross sections derived from
potential models and also from pionless effective field theory. Choosing the
spread of the reaction yields, caused basically by the different ways the
two-body currents are treated, as a measure of the model dependent uncertainty,
we conclude that the breakup reactions are 2 - 3 % uncertain, and that
even the ratio of the charged to neutral current reaction rates is also
2 % uncertain.Comment: 13 pages, 1 figure, 6 tables, version published in Phys. Rev. C 75,
044610 (2007
The role of the pion pair term in the theory of the weak axial meson exchange currents
The structure of the weak axial pion exchange current is discussed in various
models. It is shown how the interplay of the chiral invariance and the double
counting problem restricts uniquely the form of the pion potential term, in the
case when the nuclear dynamics is described by the Schroedinger equation with
the static nucleon-nucleon potential.Comment: 17 pages, 1 figure, 2 tables, stylistic changes of the tex
Chemical Enrichment at High Redshifts: Understanding the Nature of Damped Ly Systems in Hierarchical Models
We use cosmological hydrodynamical simulations including star formation and
metal enrichment to study the evolution of the chemical properties of
galaxy-like objects at high redshift in the range in a
hierarchical clustering scenario. As the galactic objects are assembled we find
that their gaseous components exhibit neutral Hydrogen column densities with
abundances and scatter comparable to those observed in damped Lyman-
systems (DLAs).The unweighted mean of abundance ratios and least square linear
regressions through the simulated DLAs yield intrinsic metallicity evolution
for the [Zn/H] and [Fe/H], consistent with results obtained from similar
analysis of available observations. Our model statistically reproduces the mild
evolution detected in the metallicity of the neutral hydrogen content of the
Universe, given by mass-weighted means,if observational constraints are
considered (as suggested by Boiss\'ee et al. 1998). For the -elements
in the simulated DLAs, we find neither enhancement nor dependence on
metallicity. Our results support the hypotheses that DLAs trace a variety of
galactic objects with different formation histories and that both SNI and SNII
are contributing to the chemical enrichment of the gas component at least since
. This study indicates that DLAs could be understood as the
building blocks that merged to form today normal galaxies within a hierarchical
clustering scenario.Comment: 2 Postscript figures.Acepted Ap
Nitrogen Abundances in DLA Systems: The Combined Effects of SNII and SNIa in a Hierarchical Clustering Scenario
The combined enrichment of Supernovae II and I in a hierarchical clustering
scenario could produce regions with low N content respect to -elements
consistent with observed values measured in Damped Ly- (DLAs). We have
studied the formation of DLAs in a hierarchical clustering scenario under the
hypothesis that the building blocks of current field galaxies could be part of
the structures mapped by DLAs. In our models the effects of the non-linear
evolution of the structure (which produces bursty star formation histories, gas
infall, etc.) and the contributions of SNIa and SNII are found to be
responsible of producing these N regions with respect to the -elements.
Although SNIa are not main production sites for Si or O, because of the
particular timing Consistently, we found the simulated low nitrogen DLAs to
have sub-solar [Fe/H]. We show that low nitrogen DLAs have experienced
important star formation activity in the past with higher efficiency than
normal DLAs. Our chemical model suggests that SNIa play a relevant role in the
determination of the abundance pattern of DLA and, that the observed low
nitrogen DLA frequency could be explained taking into account the time-delay of
0.5 Gyr introduced by these supernova to release metals.Comment: 4 pages, 2 Postscript figures. Accepted for publication in MNRAS
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