1,074 research outputs found
Bakamjian-Thomas mass operator for the few-nucleon system from chiral dynamics
We present an exploratory study consisting in the formulation of a
relativistic quantum mechanics to describe the few-nucleon system at low
energy, starting from the quantum field theoretical chiral Lagrangian involving
pions and nucleons. To this aim we construct a Bakamjian-Thomas mass operator
and perform a truncation of the Fock space which respects at each stage the
relativistic covariance. Such truncation is justified, at sufficiently low
energy, in the framework of a systematic chiral expansion. As an illustration
we discuss the bound state observables and low-energy phaseshifts of the
nucleon-nucleon and pion-nucleon scattering at the leading order of our scheme.Comment: 17 pages, 10 figures. Revised formulation, matches the journal
versio
Fermionic bound states in Minkowski-space: Light-cone singularities and structure
The Bethe-Salpeter equation for two-body bound system with spin
constituent is addressed directly in the Minkowski space. In order to
accomplish this aim we use the Nakanishi integral representation of the
Bethe-Salpeter amplitude and exploit the formal tool represented by the exact
projection onto the null-plane. This formal step allows one i) to deal with
end-point singularities one meets and ii) to find stable results, up to
strongly relativistic regimes, that settles in strongly bound systems. We apply
this technique to obtain the numerical dependence of the binding energies upon
the coupling constants and the light-front amplitudes for a fermion-fermion
state with interaction kernels, in ladder approximation, corresponding to
scalar-, pseudoscalar- and vector boson exchanges, respectively. After
completing the numerical survey of the previous cases, we extend our approach
to a quark-antiquark system in state, taking both constituent-fermion and
exchanged boson masses, from lattice calculations. Interestingly, the
calculated light-front amplitudes for such a mock pion show peculiar signatures
of the spin degrees of freedom.Comment: 22 pages, 7 figures, bst file include
The importance of few-nucleon physics at low energy
This manuscript originated from the discussion at the workshop on the "Future
of Few-body Low Energy Experimental Physics" (FFLEEP), which was held at the
University of Trento on December 4-7, 2002 and has been written in its present
form on March 19, 2003. It illustrates a selection of theoretical advancements
in the nuclear few-body problem, including two- and many-nucleon interactions,
the three-nucleon bound and scattering system, the four-body problem, the
A-body (A4) problem, and fields of related interest, such as reactions of
astrophysical interest and few-neutron systems. Particular attention is called
to the contradictory situation one experiences in this field: while theory is
currently advancing and has the potential to inspire new experiments, the
experimental activity is nevertheless rapidly phasing out. If such a trend will
continue, advancements in this area will become critically difficult.Comment: 29 pages, 21 figures. Manuscript originated from the discussion at
the workshop on the "Future of Few-body Low Energy Experimental Physics"
(FFLEEP), University of Trento, December 4-7, 2002, written in its present
form on March 19, 2003, circulated mainly among the participants to the
FFLEEP workshop. Since the authors have been repeatedly solicited to make the
manuscript accessible to a larger audience potentially interested in its
scientific content, they have decided to post it on this archiv
Realistic Calculation of the hep Astrophysical Factor
The astrophysical factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to a realistic Hamiltonian consisting of the Argonne v18
two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak charge
and current operators have vector and axial-vector components, that include
one- and many-body terms. All possible multipole transitions connecting any of
the p-3He S- and P-wave channels to the 4He bound state are considered. The
S-factor at a p-3He center-of-mass energy of 10 keV, close to the Gamow-peak
energy, is predicted to be 10.1 10^{-20} keV b, a factor of five larger than
the standard-solar-model value. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor.Comment: 8 pages RevTex file, submitted to Phys. Rev. Let
The Ay Problem for p-3He Elastic Scattering
We present evidence that numerically accurate quantum calculations employing
modern internucleon forces do not reproduce the proton analyzing power, A_y,
for p-3He elastic scattering at low energies. These calculations underpredict
new measured analyzing powers by approximately 30% at E_{c.m.} = 1.20 MeV and
by 40% at E_{c.m.} = 1.69 MeV, an effect analogous to a well-known problem in
p-d and n-d scattering. The calculations are performed using the complex Kohn
variational principle and the (correlated) Hyperspherical Harmonics technique
with full treatment of the Coulomb force. The inclusion of the three-nucleon
interaction does not improve the agreement with the experimental data.Comment: Latex file, 4 pages, 2 figures, to be published on Phys. Rev. Let
Application of EFT at Thermal Energies
We have been evaluated some observables of n-d systems by using pionless
Effective Field Theory(\EFTNoPion) and insertion of the three-body force up to
next-to-next to leading order(NLO). The evaluated data has been compared
with experimental and the three-nucleon calculation of the total cross section
with modern realistic two- and three-nucleon forces AV18/UrbIX potential models
calculations.Comment: 3 pages, 1 figure and 1 table. Talk given at 20th European Conference
on Few-Body Problems in Physics (EFB 20), Pisa, Italy, 10-14 Sep 200
Polarization observables in p-d scattering below 30 MeV
Differential and total breakup cross sections as well as vector and tensor
analyzing powers for p-d scattering are studied for energies above the deuteron
breakup threshold up to E(lab)=28 MeV. The p-d scattering wave function is
expanded in terms of the correlated hyperspherical harmonic basis and the
elastic S-matrix is obtained using the Kohn variational principle in its
complex form. The effects of the Coulomb interaction, which are expected to be
important in this energy range, have been rigorously taken into account. The
Argonne AV18 interaction and the Urbana URIX three-nucleon potential have been
used to perform a comparison to the available experimental data.Comment: 31 pages, 8 figure
Structure of A=3 Nuclear Systems Using Realistic Hamiltonians
The structure of A=3 low-energy scattering states is described using the
hyperspherical harmonics method with realistic Hamiltonian models, consisting
of two- and three-nucleon interactions. Both coordinate and momentum space
two-nucleon potential models are considered.Comment: 3 pages, 1 table, Proceedings of the 20th European Conference on
Few-Body Problems in Physics (EFB20), Pisa, September 200
Variational Calculation on A=3 and 4 Nuclei with Non-Local Potentials
The application of the hyperspherical harmonic approach to the case of
non-local two-body potentials is described. Given the properties of the
hyperspherical harmonic functions, there are no difficulties in considering the
approach in both coordinate and momentum space. The binding energies and other
ground state properties of A=3 and 4 nuclei are calculated using the CD Bonn
2000 and N3LO two-body potentials. The results are shown to be in excellent
agreement with corresponding ones obtained by other accurate techniques.Comment: 12 pages, 6 tables, RevTex
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
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