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 $\sim$ 2 - 3 % uncertain, and that even the ratio of the charged to neutral current reaction rates is also $\sim$ 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 Lyα\alpha 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 $0.25<z< 2.35$ 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-$\alpha$ 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 $\alpha$-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 $z \approx 2$. 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 $\alpha$-elements consistent with observed values measured in Damped Ly-$\alpha$ (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 $\alpha$-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 $\approx$ 0.5 Gyr introduced by these supernova to release metals.Comment: 4 pages, 2 Postscript figures. Accepted for publication in MNRAS (pink pages