98 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
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
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
Three-nucleon contact interaction at the next-to-leading order
A satisfactory description of bound and scattering states of the
three-nucleon (3N) system is still lacking, contrary to what happens in the
two-nucleon case. In the framework of chiral effective theory, it is possible
that a realistic 3N interaction will require the inclusion of subleading
contact terms, which are unconstrained by chiral symmetry. We construct the
minimal 3N contact Lagrangian imposing all constraints from the discrete
symmetries, Fierz identities and Poincar\'e covariance, and show that it
consists of 10 independent operators. By integrating out the pions from the
effective theory we derive the pion-induced contributions to the corresponding
low-energy constants (LECs), and find no clear signal of convergence of the
pionful theory between N2LO and N3LO.Comment: 6 pages, presented at the Sixth International Conference on Quarks
and Nuclear Physics, April 16-20, 2012. Ecole Polytechnique, Palaiseau,
Paris, Franc
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
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
Efimov physics and connections to nuclear physics
Physical systems characterized by a shallow two-body bound or virtual state are governed at large distances by continuous scale invariance, which is broken into discrete scale invariance when three or more particles come into play. This symmetry induces a universal behavior for different systems that is independent of the details of the underlying interaction and rooted in the smallness of the ratio l/aB << 1, where the length aB is associated with the binding energy of the two-body system E2 = h2 /ma2B, and l is the natural length given by the interaction range. Efimov physics refers to this universal behavior, which is often hidden by the onset of system-specific nonuniversal effects. In this review, we identify universal properties by providing an explicit link of physical systems to their unitary limit, in which aB → ∞, and we show that nuclear systems belong to this class of universality
Proton-3He elastic scattering at low energies and the "A_y Puzzle"
The Kohn variational principle and the hyperspherical harmonic technique are
applied to study p-3He elastic scattering at low energies. Preliminary results
obtained using several interaction models are reported. The calculations are
compared to a recent phase shift analysis performed at the Triangle University
Nuclear Laboratory and to the available experimental data. Using a
three-nucleon interaction derived from chiral perturbation theory at N2LO, we
have found a noticeable reduction of the discrepancy observed for the A_y
observable.Comment: 9 pages, 9 figures, to be published in the Proceedings of the 19th
International IUPAP Conference on Few-Body Problems in Physics, Bonn, 200
Unitary ambiguity of NN contact interactions and the 3N force
We identify a redundancy between two- and three-nucleon contact interactions
at the fourth and fifth order of the chiral expansion respectively. In
particular we show that tensor-type and spin-orbit three-nucleon contact
interactions effectively account for that part of the two-nucleon interaction
which depends on the total center-of-mass momentum and is unconstrained by
relativity. This might give the chiral effective field theory enough
flexibility to successfully address scattering observables already at
N3LO.Comment: 9 pages, discussion extended to OPE 3N
Short-range three-nucleon interaction from A=3 data and its hierarchical structure
We construct accurate models of the three-nucleon (3N) interaction by fitting, in a hybrid phenomenological approach, the low-energy constants parametrizing the subleading 3N contact operators to the triton binding energy, n-d scattering lengths, cross section, and polarization observables of p-d scattering at 2 MeV center-of-mass energy. These models lead to a satisfactory description of polarized p-d scattering data in the whole energy range below the deuteron breakup threshold. In particular, the longstanding Ay puzzle seems to be solved thanks to the new terms considered in the 3N force. Two types of hierarchies among the subleading contact operators are also derived, based on the large-Nc counting and on a recently proposed relativistic counting. We test these hierarchies against the same experimental data and show that they are respected at a reasonable level
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