552 research outputs found
Can the nuclear symmetry potential at supra-saturation densities be negative?
In the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU)
transport model, for the central Au+Au reaction at an incident
beam energy of 400 MeV/nucleon, effect of nuclear symmetry potential at
supra-saturation densities on the pre-equilibrium clusters emission is studied.
It is found that for the positive symmetry potential at supra-saturation
densities the neutron to proton ratio of lighter clusters with mass number
() is larger than that of the weighter clusters with
mass number (), whereas for the negative symmetry potential
at supra-saturation densities the is \emph{smaller} than that
of the . This may be considered as a probe of the negative
symmetry potential at supra-saturation densities.Comment: 5 pages, 3 figures, 1 table, to be publishe
Google Books: Page by Page, Click by Click, Users Are Reading Away Privacy Rights
Google Books will likely become the world\u27s most extensive book and magazine search and browsing resource, library, and bookstore--combined. However, as users necessarily reveal personal identifying information through their book searches and reading habits, this service poses a significant threat to personal privacy.
Because the Google Books Amended Settlement Agreement neglects to meaningfully address user privacy, the only available privacy protections are the limited rights bestowed by the Google Books Privacy Policy and the Google Privacy Policy. Unfortunately, these Privacy Policies protect the interests of Google at the expense of users.
The enactment of federal privacy statutes, which include provisions for electronic privacy, underscores the importance of protecting certain types of personal information. Moreover, just as the Constitution has historically protected reading habits and freedom of thought from governmental intrusion, Congress should extend privacy protections for such innately personal data to corporations as well. Additionally, safeguards long-recognized by traditional libraries should be maintained by Internet content providers like Google Books as they provide a functionally similar service.
This Note proposes a solution to the privacy concerns raised by services like Google Books: the enactment of a comprehensive federal statute that protects the privacy of personal electronic information. Specifically, such a statute would require: (1) transparency to make consumers aware of what data companies collect and store and what consumers implicitly authorize those companies to do with that data merely by using online products; (2) boundaries on what user information can be tracked and limits on the time frame in which it can be retained; (3) user access to personal information; and (4) protection against release of acquired information to other parties
Momentum, Density, and Isospin dependence of the Symmetric and Asymmetric Nuclear Matter Properties
Properties of symmetric and asymmetric nuclear matter have been investigated
in the relativistic Dirac-Brueckner-Hartree-Fock approach based on projection
techniques using the Bonn A potential. The momentum, density, and isospin
dependence of the optical potentials and nucleon effective masses are studied.
It turns out that the isovector optical potential depends sensitively on
density and momentum, but is almost insensitive to the isospin asymmetry.
Furthermore, the Dirac mass and the nonrelativistic mass
which parametrizes the energy dependence of the single particle spectrum, are
both determined from relativistic Dirac-Brueckner-Hartree-Fock calculations.
The nonrelativistic mass shows a characteristic peak structure at momenta
slightly above the Fermi momentum \kf. The relativistic Dirac mass shows a
proton-neutron mass splitting of in isospin asymmetric
nuclear matter. However, the nonrelativistic mass has a reversed mass splitting
which is in agreement with the results from
nonrelativistic calculations.Comment: 25 pages, 12 figures, to appear in Physical Review
Electromagnetic form factors of the baryon octet in the perturbative chiral quark model
We apply the perturbative chiral quark model at one loop to analyze the
electromagnetic form factors of the baryon octet. The analytic expressions for
baryon form factors, which are given in terms of fundamental parameters of
low-energy pion-nucleon physics (weak pion decay constant, axial nucleon
coupling, strong pion-nucleon form factor), and the numerical results for
baryon magnetic moments, charge and magnetic radii are presented. Our results
are in good agreement with experimental data.Comment: 15 pages, 6 figures, to be published in Eur. Phys. J.
MesonNet Workshop on Meson Transition Form Factors
The mini-proceedings of the Workshop on Meson Transition Form Factors held in
Cracow from May 29th to 30th, 2012 introduce the meson transition form factor
project with special emphasis on the interrelations between the various form
factors (on-shell, single off-shell, double off-shell). Short summaries of the
talks presented at the workshop follow.Comment: 69 pages, 14 figures; all talks can be found at
https://sites.google.com/site/mesonnetwork/home/activities/form-factor-workshop-2012;
v2: workshop link updated (as the page had to be moved to a commercial
server), table 6 correcte
Reconciling threshold and subthreshold expansions for pion-nucleon scattering
Heavy-baryon chiral perturbation theory (ChPT) at one loop fails in relating
the pion-nucleon amplitude in the physical region and for subthreshold
kinematics due to loop effects enhanced by large low-energy constants. Studying
the chiral convergence of threshold and subthreshold parameters up to fourth
order in the small-scale expansion, we address the question to what extent this
tension can be mitigated by including the as an explicit degree
of freedom and/or using a covariant formulation of baryon ChPT. We find that
the inclusion of the indeed reduces the low-energy constants to more
natural values and thereby improves consistency between threshold and
subthreshold kinematics. In addition, even in the -less theory the
resummation of corrections in the covariant scheme improves the results
markedly over the heavy-baryon formulation, in line with previous observations
in the single-baryon sector of ChPT that so far have evaded a profound
theoretical explanation.Comment: 10 pages, 4 tables, Mathematica notebook with the analytic
expressions for threshold and subthreshold parameters included as
supplementary material; journal versio
Isospin mixing in the nucleon and 4He and the nucleon strange electric form factor
In order to isolate the contribution of the nucleon strange electric form
factor to the parity-violating asymmetry measured in 4He(\vec e,e')4He
experiments, it is crucial to have a reliable estimate of the magnitude of
isospin-symmetry-breaking (ISB) corrections in both the nucleon and 4He. We
examine this issue in the present letter. Isospin admixtures in the nucleon are
determined in chiral perturbation theory, while those in 4He are derived from
nuclear interactions, including explicit ISB terms. A careful analysis of the
model dependence in the resulting predictions for the nucleon and nuclear ISB
contributions to the asymmetry is carried out. We conclude that, at the low
momentum transfers of interest in recent measurements reported by the HAPPEX
collaboration at Jefferson Lab, these contributions are of comparable magnitude
to those associated with strangeness components in the nucleon electric form
factor.Comment: 4 pages, 2 figures, revtex
Investigation of a0-f0 mixing
We investigate the isospin-violating mixing of the light scalar mesons
a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating
effects are considered to leading order in the quark mass differences and
electromagnetism. In this approach both mesons are generated through
meson-meson dynamics. Our results provide a description of the mixing
phenomenon within a framework consistent with chiral symmetry and unitarity,
where these resonances are not predominantly q q-bar states. Amongst the
possible experimental signals, we discuss observable consequences for the
reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the
effect of a0-f0 mixing is by far the most important isospin-breaking effect in
the resonance region and can indeed be extracted from experiment.Comment: 15 pages, 9 figures; discussion extended, title changed, version
published in Phys. Rev.
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