1,291 research outputs found
A new way to perform partial wave decompositions of few-nucleon forces
We formulate a general and exact method of partial wave decomposition (PWD)
of any nucleon-nucleon (NN) potential and any three-nucleon (3N) force. The
approach allows one to efficiently use symbolic algebra software to generate
the interaction dependent part of the program code calculating the interaction.
We demonstrate the feasibility of this approach for the one-boson exchange
BonnB potential, a recent nucleon-nucleon chiral force and the chiral
two-pion-exchange three-nucleon force. In all cases very good agreement between
the new and the traditional PWD is found. The automated PWD offered by the new
approach is of the utmost importance in view of future applications of numerous
chiral N3LO contributions to the 3N force in three nucleon calculations.Comment: 10 pages, 6 figures (24 eps files
3N Scattering in a Three-Dimensional Operator Formulation
A recently developed formulation for a direct treatment of the equations for
two- and three-nucleon bound states as set of coupled equations of scalar
functions depending only on vector momenta is extended to three-nucleon
scattering. Starting from the spin-momentum dependence occurring as scalar
products in two- and three-nucleon forces together with other scalar functions,
we present the Faddeev multiple scattering series in which order by order the
spin-degrees can be treated analytically leading to 3D integrations over scalar
functions depending on momentum vectors only. Such formulation is especially
important in view of awaiting extension of 3N Faddeev calculations to
projectile energies above the pion production threshold and applications of
chiral perturbation theory 3N forces, which are to be most efficiently treated
directly in such three-dimensional formulation without having to expand these
forces into a partial wave basis.Comment: 25 pages, 0 figure
Energy Dependence of the NN t-matrix in the Optical Potential for Elastic Nucleon-Nucleus Scattering
The influence of the energy dependence of the free NN t-matrix on the optical
potential of nucleon-nucleus elastic scattering is investigated within the
context of a full-folding model based on the impulse approximation. The
treatment of the pole structure of the NN t-matrix, which has to be taken into
account when integrating to negative energies is described in detail. We
calculate proton-nucleus elastic scattering observables for O,
Ca, and Pb between 65 and 200 MeV laboratory energy and study
the effect of the energy dependence of the NN t-matrix. We compare this result
with experiment and with calculations where the center-of-mass energy of the NN
t-matrix is fixed at half the projectile energy. It is found that around 200
MeV the fixed energy approximation is a very good representation of the full
calculation, however deviations occur when going to lower energies (65 MeV).Comment: 11 pages (revtex), 6 postscript figure
Different Methods for the Two-Nucleon T-Matrix in the Operator Form
We compare three methods to calculate the nucleon-nucleon t-matrix based on
the three-dimensional formulation of J. Golak et al., Phys. Rev. C 81, 034006,
(2010). In the first place we solve a system of complex linear inhomogeneous
equations directly for the t-matrix. Our second method is based on iterations
and a variant of the Lanczos algorithm. In the third case we obtain the
t-matrix in two steps, solving a system of real linear equations for the
k-matrix expansion coefficients and then solving an on-shell equation, which
connects the scalar coefficients of the k- and t-matrices. A very good
agreement among the three methods is demonstrated for selected nucleon-nucleon
scattering observables using a chiral next-to-next-to-leading-order
neutron-proton potential. We also apply our three-dimensional framework to the
demanding problem of proton-proton scattering, using a corresponding version of
the nucleon-nucleon potential and supplementing it with the (screened) Coulomb
force, taken also in the three-dimensional form. We show converged results for
two different screening functions and find a very good agreement with other
methods dealing with proton-proton scattering.Comment: 18 pages, 10 figures (54 eps files
Excesses in the Cosmic Ray Spectrum and Possible Interpretations
The data collected by ATIC, PPB-BETS, FERMI-LAT and HESS all indicate that
there is an electron/positron excess in the cosmic ray energy spectrum above
100 GeV, although different instrumental teams do not agree on the
detailed spectral shape. PAMELA also reported a clear excess feature of the
positron fraction above several GeV, but no excess in anti-protons. Here we
review the observational status and theoretical models of this interesting
observational feature. We pay special attention to various physical
interpretations proposed in the literature, including modified supernova
remnant models for the background, new astrophysical sources, and new
physics (the dark matter models). We suggest that although most models can make
a case to interpret the data, with the current observational constraints the
dark matter interpretations, especially those invoking annihilation, require
much more exotic assumptions than some astrophysical interpretations. Future
observations may present some ``smoking-gun'' observational tests to
differentiate among different models and to identify the correct interpretation
to the phenomenon.Comment: 48 pages, including 10 figures and 1 tabel. Invited review to be
published in IJMP
Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials
The sensitivity of nucleon-nucleus elastic scattering to the off-shell
behavior of realistic nucleon-nucleon interactions is investigated when
on-shell equivalent nucleon-nucleon potentials are used. The study is based on
applications of the full-folding optical model potential for an explicit
treatment of the off-shell behavior of the nucleon-nucleon effective
interaction. Applications were made at beam energies between 40 and 500 MeV for
proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris
potential and its local on-shell equivalent as obtained with the
Gelfand-Levitan and Marchenko inversion formalism for the two nucleon
Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering
show small fluctuations in the corresponding observables. This implies that
off-shell features of the NN interaction cannot be unambiguously identified
with these processes. Inversion potentials were also constructed directly from
NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in
proton-nucleus scattering above 200 MeV provide a superior description of the
observables relative to those obtained from current realistic NN potentials.
Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.
Full-Folding Optical Potentials for Elastic Nucleon-Nucleus Scattering based on Realistic Densities
Optical model potentials for elastic nucleon nucleus scattering are
calculated for a number of target nuclides from a full-folding integral of two
different realistic target density matrices together with full off-shell
nucleon-nucleon t-matrices derived from two different Bonn meson exchange
models. Elastic proton and neutron scattering observables calculated from these
full-folding optical potentials are compared to those obtained from `optimum
factorized' approximations in the energy regime between 65 and 400 MeV
projectile energy. The optimum factorized form is found to provide a good
approximation to elastic scattering observables obtained from the full-folding
optical potentials, although the potentials differ somewhat in the structure of
their nonlocality.Comment: 21 pages, LaTeX, 17 postscript figure
Three-Nucleon Photodisintegration of 3He
The three-nucleon photodisintegration of 3He has been calculated in the whole
phase space using consistent Faddeev equations for the three-nucleon bound and
scattering states. Modern nucleon-nucleon and 3N forces have been applied as
well as different approaches to nuclear currents. Phase space regions are
localized where 3N force effects are especially large. In addition
semi-exclusive cross sections for 3He(gamma,N) have been predicted which carry
interesting peak structures. Finally some data for the exclusive 3N breakup
process of 3He and its total breakup cross section have been compared to
theory.Comment: 28 pages, 6 png figures, 11 ps figures, modified version with changed
figures, conclusions unchanged, to appear in Phys.Rev.
Social democracy, embeddedness and decommodification: On the conceptual innovations and intellectual affiliations of Karl Polanyi
Of the several debates that revolve around the work of the economic historian and political economist Karl Polanyi, one that continues to exercise minds concerns his analysis of, and political attitudes toward, post-war capitalism and the welfare state. Simplified a little, it is a debate with two sides. To borrow Iván Szelényi's terms, one side constructs a ‘hard’ Karl Polanyi, the other a ‘soft’ one. The former advocated a socialist mixed economy dominated by redistributive mechanisms. He was a radical socialist for whom the market should never be the dominant mechanism of economic coordination. His ‘soft’ alter ego insisted that the market system remain essentially intact but be complemented by redistributive mechanisms. The ‘double movement’ – the central thesis of his ‘Great Transformation’ – acts, in this reading, as a self-correcting mechanism that moderates the excesses of market fundamentalism; its author was positioned within the social-democratic mainstream for which the only realistic desirable goal is a regulated form of capitalism. In terms of textual evidence there is much to be said for both interpretations. In this article I suggest a different approach, one that focuses upon the meaning of Polanyi's concepts in relation to their socio-political and intellectual environment
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