1,993 research outputs found
Subleading contributions to the three-nucleon contact interaction
We obtain a minimal form of the two-derivative three-nucleon contact
Lagrangian, by imposing all constraints deriving from discrete symmetries,
Fierz identities and Poincare' covariance. The resulting interaction, depending
on 13 unknown low-energy constants, leads to a three-nucleon potential which we
give in a local form in configuration space. We also consider the leading
(no-derivative) four-nucleon interaction and show that there exists only one
independent operator.Comment: 11 pages. Three more operators found after correcting some mistaken
Fierz relation
The proton-proton weak capture in chiral effective field theory
The astrophysical S-factor for proton-proton weak capture is calculated in
chiral effective field theory over the center-of-mass relative-energy range
0--100 keV. The chiral two-nucleon potential derived up to
next-to-next-to-next-to leading order is augmented by the full electromagnetic
interaction including, beyond Coulomb, two-photon and vacuum-polarization
corrections. The low-energy constants (LEC's) entering the weak current
operators are fixed so as to reproduce the A=3 binding energies and magnetic
moments, and the Gamow-Teller matrix element in tritium beta decay.
Contributions from S and P partial waves in the incoming two-proton channel are
retained. The S-factor at zero energy is found to be S(0)=(4.030 +/- 0.006) x
10^{-23} MeV fm^2, with a P-wave contribution of 0.020 x 10^{-23} MeV fm^2. The
theoretical uncertainty is due to the fitting procedure of the LEC's and to the
cutoff dependence.Comment: 4 pages, 3 figures; revisited version accepted for publication on
Phys. Rev. Lett. A misprint in Table II has been correcte
Effect of three nucleon forces in p-3He scattering
The effect of the inclusion of different models of three nucleon (3N) forces
in p-3He elastic scattering at low energies is studied. Two models have been
considered: one derived from effective field theory at next-to-next-to-leading
order and one derived from a more phenomenological point of view -- the
so-called Illinois model. The four nucleon scattering observables are
calculated using the Kohn variational principle and the hyperspherical harmonic
technique and the results are compared with available experimental data. We
have found that with the inclusion of both 3N force models the agreement with
the experimental data is improved, in particular for the proton vector
analyzing power A_y.Comment: 8 pages, 4 figures, talk presented at the 20th International IUPAP
Conference on Few-Body Problems in Physics, 20 - 25 August, 2012, Fukuoka,
Japa
Effect of three-nucleon interaction in p-3He elastic scattering
We present a detailed study of the effect of different three-nucleon
interaction models in p-3He elastic scattering at low energies. In particular,
two models have been considered: one derived from effective field theory at
next-to-next-to-leading order and one derived from a more phenomenological
point of view -- the so-called Illinois model. The four-nucleon scattering
observables are calculated using the Kohn variational principle and the
hyperspherical harmonics technique and the results are compared with available
experimental data. We have found that the inclusion of either one of the other
force model improves the agreement with the experimental data, in particular
for the proton vector analyzing power.Comment: 4 pages, 3 figure
Comparative study of three-nucleon force models in systems
Using modern nucleon-nucleon interactions in the description of the
nuclei, it is not possible to reproduce both the three- and four-nucleon
binding energies simultaneously. This is one manifestation of the necessity of
including a three-nucleon force in the nuclear Hamiltonian. In this paper we
will perform a comparative study of some, widely used, three-nucleon force
models. We will analyze their capability to describe the aforementioned binding
energies as well as the doublet scattering length. A correct description
of these quantities can be considered a stringent requirement for a nuclear
Hamiltonian containing two- and three-nucleon interaction terms. As we will
show, this requirement is not fulfilled by several of the models available in
the literature. To satisfy it, we propose modifications in the parametrization
of the three-nucleon forces and we study their effects on few selected
low energy scattering observables.Comment: 30 pages, 10 figure
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
The two-nucleon electromagnetic charge operator in chiral effective field theory (EFT) up to one loop
The electromagnetic charge operator in a two-nucleon system is derived in
chiral effective field theory (EFT) up to order (or N4LO), where
denotes the low-momentum scale and is the electric charge. The specific
form of the N3LO and N4LO corrections from, respectively, one-pion-exchange and
two-pion-exchange depends on the off-the-energy-shell prescriptions adopted for
the non-static terms in the corresponding potentials. We show that different
prescriptions lead to unitarily equivalent potentials and accompanying charge
operators. Thus, provided a consistent set is adopted, predictions for physical
observables will remain unaffected by the non-uniqueness associated with these
off-the-energy-shell effects.Comment: 16 pages, 10 figure
Implications of Efimov physics for the description of three and four nucleons in chiral effective field theory
In chiral effective field theory the leading order (LO) nucleon-nucleon
potential includes two contact terms, in the two spin channels , and the
one-pion-exchange potential. When the pion degrees of freedom are integrated
out, as in the pionless effective field theory, the LO potential includes two
contact terms only. In the three-nucleon system, the pionless theory includes a
three-nucleon contact term interaction at LO whereas the chiral effective
theory does not. Accordingly arbitrary differences could be observed in the LO
description of three- and four-nucleon binding energies. We analyze the two
theories at LO and conclude that a three-nucleon contact term is necessary at
this order in both theories. In turn this implies that subleading three-nucleon
contact terms should be promoted to lower orders. Furthermore this analysis
shows that one single low energy constant might be sufficient to explain the
large values of the singlet and triplet scattering lengths.Comment: 5 pages, 3 figure
Electromagnetic Structure and Reactions of Few-Nucleon Systems in EFT
We summarize our recent work dealing with the construction of the
nucleon-nucleon potential and associated electromagnetic currents up to one
loop in chiral effective field theory (EFT). The magnetic dipole
operators derived from these currents are then used in hybrid calculations of
static properties and low-energy radiative capture processes in few-body
nuclei. A preliminary set of results are presented for the magnetic moments of
the deuteron and trinucleons and thermal neutron captures on , , and
He.Comment: Invited talk to the 19th International IUPAP Conference on Few-Body
Problems in Physic
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