3,266 research outputs found
Coherent pion production off nuclei at T2K and MiniBooNE energies revisited
As a result of a new improved fit to old bubble chamber data of the dominant
axial C_5^A nucleon-to-Delta form factor, and due to the relevance of this form
factor for neutrino induced coherent pion production, we re-evaluate our model
predictions in Phys. Rev. D79, 013002 (2009) for different observables of the
latter reaction. Central values for the total cross sections increase by 20% to
30%, while differential cross sections do not change their shape appreciably.
Furthermore, we also compute the uncertainties on total, differential and flux
averaged cross sections induced by the errors in the determination of C_5^A.
Our new results turn out to be compatible within about 1 sigma with the former
ones. Finally, we stress the existing tension between the recent experimental
determination of the sigma(CC coh \pi^+)/sigma(NC coh \pi^0) ratio by the
SciBooNE Collaboration and the theoretical predictions.Comment: 6 latex pages, 1 table, 2 figures. Shortened versio
Crossover from Endogenous to Exogenous Activity in Open-Source Software Development
We have investigated the origin of fluctuations in the aggregated behaviour
of an open-source software community. In a recent series of papers, de Menezes
and co-workers have shown how to separate internal dynamics from external
fluctuations by capturing the simultaneous activity of many system's
components. In spite of software development being a planned activity, the
analysis of fluctuations reveals how external driving forces can be only
observed at weekly and higher time scales. Hourly and higher change frequencies
mostly relate to internal maintenance activities. There is a crossover from
endogenous to exogenous activity depending on the average number of file
changes. This new evidence suggests that software development is a
non-homogeneous design activity where stronger efforts focus in a few project
files. The crossover can be explained with a Langevin equation associated to
the cascading process, where changes to any file trigger additional changes to
its neighbours in the software network. In addition, analysis of fluctuations
enables us to detect whether a software system can be decomposed in several
subsystems with different development dynamics.Comment: 7 pages, 4 figures, submitted to Europhysics Letter
New determination of the - axial form factors from weak pion production and coherent pion production off nuclei at T2K and MiniBooNE energies revisited
We re-evaluate our model predictions in Phys. Rev. D 79, 013002 (2009) for
different observables in neutrino induced coherent pion production. This comes
as a result of the new improved fit to old bubble chamber data of the dominant
axial C_5^A nucleon-to-Delta form factor. We find an increase of 20%-30% in the
values for the total cross sections. Uncertainties induced by the errors in the
determination of C_5^A are computed. Our new results turn out to be compatible
within about with the former ones. We also stress the existing
tension between the recent experimental determination of the \sigma(CC coh
\pi^+)}/\sigma(NC coh \pi^0)} $ ratio by the SciBooNE Collaboration and the
theoretical predictions.Comment: 3 latex pages, 1 figure. Talk given at the NuFact10 Conferenc
Neutrino induced coherent pion production
We discuss different parameterizations of the axial
form factor, fitted to the old Argonne bubble chamber data for pion production
by neutrinos, and we use coherent pion production to test their low
behavior. We find moderate effects that will be difficult to observe with the
accuracy of present experiments. We also discuss the use of the Rein-Sehgal
model for low energy coherent pion production. By comparison to a microscopic
calculation, we show the weaknesses of some of the approximations in that model
that lead to very large cross sections as well as to the wrong shapes for
differential ones. Finally we show that models based on the partial
conservation of the axial current hypothesis are not fully reliable for
differential cross sections that depend on the angle formed by the pion and the
incident neutrino.Comment: Talk given at NUFACT09. 6 latex pages, 7 figures, 1 tabl
Local Fermi gas in inclusive muon capture from nuclei
We compare local Fermi gas and shell model in muon capture in nuclei in order
to estimate the effect of finite nuclear size in low energy weak reactions.Comment: 6 pages, 8 figures. To be published in the Proceedings of 20th Max
Born Symposium, Wroclaw (Poland), December 7-10, 200
Nucleon Emision Off Nuclei Induced By Neutrino Interactions
We make a review of the main nuclear effects that affect neutrino-nucleus
cross sections. We discuss how the different models in the literature try to
describe these different effects, and thus try to compare between them. We
focus on the quasi-elastic reaction in the neutrino energy region of around 1
GeV, where recent data from MiniBoone are available. Among the issues discussed
are the different treatment of medium corrections to initial and nal state
nucleon wave functions and the problem of the rescattering of ejected nucleons.Comment: 5 pages, 5 figures. To appear in the proceedings for NuFact09; July
20-25, (2009) Illinois Institute of Technolog
Production of Two Pions Induced by Neutrinos
We study the threshold production of two pions induced by neutrinos in
nucleon targets. The contribution of nucleon pole, pion and contact terms is
calculated using a chiral Lagrangian. The contribution of the Roper resonance,
neglected in earlier studies, has also been taken into account.Comment: Contribution to the proceedings of Chiral07, RCNP, Osaka, Japan.
Corrected version because of problems on some pdf viewer
Sustainable growth in complex networks
Based on the empirical analysis of the dependency network in 18 Java
projects, we develop a novel model of network growth which considers both: an
attachment mechanism and the addition of new nodes with a heterogeneous
distribution of their initial degree, . Empirically we find that the
cumulative degree distributions of initial degrees and of the final network,
follow power-law behaviors: , and
, respectively. For the total number of links as a
function of the network size, we find empirically ,
where is (at the beginning of the network evolution) between 1.25 and
2, while converging to for large . This indicates a transition from
a growth regime with increasing network density towards a sustainable regime,
which revents a collapse because of ever increasing dependencies. Our
theoretical framework is able to predict relations between the exponents
, , , which also link issues of software engineering and
developer activity. These relations are verified by means of computer
simulations and empirical investigations. They indicate that the growth of real
Open Source Software networks occurs on the edge between two regimes, which are
either dominated by the initial degree distribution of added nodes, or by the
preferential attachment mechanism. Hence, the heterogeneous degree distribution
of newly added nodes, found empirically, is essential to describe the laws of
sustainable growth in networks.Comment: 5 pages, 2 figures, 1 tabl
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