491 research outputs found
Numerical investigations of the three-dimensional proton-proton screened Coulomb t-matrix
We demonstrate behaviour of the momentum space screened Coulomb t-matrix,
obtained by a numerical solution of the three-dimensional Lippmann-Schwinger
equation. Examples are given for different types of screening. They prove that
it is possible to obtain numerically a reliable three-dimensional screened
Coulomb t-matrix, what is important in view of its application in few-body
calculations.Comment: 23 pages, 2 tables, 13 figures in 65 eps file
Different formulations of 3He and 3H photodisintegration
Different momentum space Faddeev-like equations and their solutions for the
radiative pd-capture and the three-nucleon photodisintegration of 3He are
presented. Applications are based on the AV18 nucleon-nucleon and the Urbana IX
three nucleon forces. Meson exchange currents are included using the Siegert
theorem. A very good agreement has been found in all cases indicating the
reliability of the used numerical methods. Predictions for cross sections and
polarization observables in the pd-capture and the complete three nucleon
breakup of 3He at different incoming deuteron/photon energies are presented.Comment: 18 pages, 9 ps figure
Deuteron disintegration in three dimensions
We compare results from the traditional partial wave treatment of deuteron
electro-disintegration with a new approach that uses three dimensional
formalism. The new framework for the two-nucleon (2N) system using a complete
set of isospin - spin states made it possible to construct simple
implementations that employ a very general operator form of the current
operator and 2N states.Comment: 24 pages, 15 eps figure
Two-Pion Exchange Currents in Photodisintegration of the Deuteron
Chiral effective field theory (ChEFT) is a modern framework to analyze the
properties of few-nucleon systems at low energies. It is based on the most
general effective Lagrangian for pions and nucleons consistent with the chiral
symmetry of QCD. For energies below the pion-production threshold it is
possible to eliminate the pionic degrees of freedom and derive nuclear
potentials and nuclear current operators solely in terms of the nucleonic
degrees of freedom. This is very important because, despite a lot of experience
gained in the past, the consistency between two-nucleon forces, many-nucleon
forces and the corresponding current operators has not been achieved yet. In
this presentation we consider the recently derived long-range two-pion exchange
(TPE) contributions to the nuclear current operator which appear at next-to
leading order of the chiral expansion. These operators do not contain any free
parameters. We study their role in the deuteron photodisintegration reaction
and compare our predictions with experimental data. The bound and scattering
states are calculated using five different chiral N2LO nucleon-nucleon (NN)
potentials which allows to estimate the theoretical uncertainty at a given
order in the chiral expansion. For some observables the results are very close
to the reference predictions based on the AV18 NN potential and the current
operator (partly) consistent with this force.Comment: Contribution to the 12th International Conference on Meson-Nucleon
Physics and the Structure of the Nucleon (MENU2010), Williamsburg, USA, May
31-June 4, 201
Relativistic effects in neutron-deuteron elastic scattering
We solved the three-nucleon Faddeev equation including relativistic features
such as relativistic kinematics, boost effects and Wigner spin rotations. As
dynamical input a relativistic nucleon-nucleon interaction exactly on-shell
equivalent to the AV18 potential has been used. The effects of Wigner rotations
for elastic scattering observables were found to be small. The boost effects
are significant at higher energies.They diminish the transition matrix elements
at higher energies and lead in spite of the increased relativistic phase-space
factor as compared to the nonrelativistic one to rather small effects in the
cross section, which are mostly restricted to the backward angles.Comment: 27 pages, 5 Postscript figure
Partial Wave Decomposition for Meson Exchange Currents in Few-Nucleon Systems
We develop an approach for calculating matrix elements of meson exchange
currents between 3N basis states in (jJ)-coupling and a 3N bound state. The
contribution generated by - and -exchange are included in the
consideration. The matrix elements are expressed in terms of multiple integrals
in the momentum space. We apply a technique of the partial wave decompositions
and carry out some angular integrations in closed form. Different
representations appropriate for numerical calculations are derived for the
matrix elements of interest. The momentum dependences of the matrix elements
are studied and benchmark results are presented. The approach developed is of
interest for the investigations of deuteron- proton radiative capture and ^3He
photo- and electrodisintegration when the interaction in the initial or final
nuclear states is taken into account by solving the Faddeev equations.Comment: 32pages (14 figures
Efficient calculation of chiral three-nucleon forces up to N3LO for ab initio studies
We present a novel framework to decompose three-nucleon forces in a momentum
space partial-wave basis. The new approach is computationally much more
efficient than previous methods and opens the way to ab initio studies of
few-nucleon scattering processes, nuclei and nuclear matter based on
higher-order chiral 3N forces. We use the new framework to calculate matrix
elements of chiral three-nucleon forces at N2LO and N3LO in large basis spaces
and carry out benchmark calculations for neutron matter and symmetric nuclear
matter. We also study the size of the individual three-nucleon force
contributions for H. For nonlocal regulators, we find that the sub-leading
terms, which have been neglected in most calculations so far, provide important
contributions. All matrix elements are calculated and stored in a user-friendly
way, such that values of low-energy constants as well as the form of regulator
functions can be chosen freely.Comment: 10 pages, 4 figure
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