10 research outputs found
Conference Discussion of the Nuclear Force
Discussion of the nuclear force, lead by a round table consisting of T.
Cohen, E. Epelbaum, R. Machleidt, and F. Gross (chair). After an invited talk
by Machleidt, published elsewhere in these proceedings, brief remarks are made
by Epelbaum, Cohen, and Gross, followed by discussion from the floor moderated
by the chair. The chair asked the round table and the participants to focus on
the following issues: (i) What does each approach (chiral effective field
theory, large Nc, and relativistic phenomenology) contribute to our knowledge
of the nuclear force? Do we need them all? Is any one transcendent? (ii) How
important for applications (few body, nuclear structure, EMC effect, for
example) are precise fits to the NN data below 350 MeV? How precise do these
fits have to be? (iii) Can we learn anything about nonperturbative QCD from
these studies of the nuclear force? The discussion presented here is based on a
video recording made at the conference and transcribed afterward.Comment: Discussion at the 21st European Conference on Few Body Problems
(EFP21) held at Salamanca, Spain, 30 Aug - 3 Sept 201
Chiral Symmetry and the Nucleon-Nucleon Interaction
We review how nuclear forces emerge from low-energy quantum chromodynamics (QCD) via chiral effective field theory (EFT). During the past two decades, this approach has evolved into a powerful tool to derive nuclear two- and many-body forces in a systematic and model-independent way. We then focus on the nucleon-nucleon (N N) interaction and show in detail how, governed by chiral symmetry, the long- and intermediate-range of the N N potential builds up order by order. We proceed up to sixth order in small momenta, where convergence is achieved. The final result allows for a full assessment of the validity of the chiral EFT approach to the N N interaction
Impact of three-body forces on elastic nucleon-nucleus scattering observables
none6siBackground: In a previous series of papers we investigated the domain of applicability of chiral potentials to the
construction of a microscopic optical potential (OP) for elastic nucleon-nucleus scattering. The OP was derived
at the first order of the spectator expansion of the Watson multiple scattering theory and its final expression
was a folding integral between the nucleon-nucleon (NN) t matrix and the nuclear density of the target. In the
calculations NN and three-nucleon (3N) chiral interactions were used for the target density and only the NN
interaction for the NN t matrix.
Purpose: The purpose of this work is to achieve another step towards the calculation of a more consistent OP
introducing the 3N force also in the dynamic part of the OP.
Methods: The full treatment of the 3N interaction is beyond our present capabilities. Thus, in the present work
it is approximated with a density dependent NN interaction obtained after the averaging over the Fermi sphere.
In practice, in our model the 3N force acts as a medium correction of the bare NN interaction used to calculate
the t matrix. Even if the 3N force is treated in an approximate way, this method naturally extends our previous
model of the OP and allows a direct comparison of our present and previous results.
Results: We consider as case studies the elastic scattering of nucleons off 12C and 16O. We present results for
the differential cross section and the spin observables for different values of the projectile energy. From the
comparison with the experimental data and with the results of our previous model we assess the importance of
the 3N interaction in the dynamic part of the OP.
Conclusions: Our analysis indicates that the contribution of the 3N force in the t matrix is small for the differential cross section and it is sizable for the spin observables, in particular, for the analyzing power. We find that the
two-pion exchange term is the major contributor to the 3N force. A chiral expansion order-by-order analysis of
the scattering observables confirms the convergence of our results at the next-to-next-to-next-to-leading-order,
as already established in our previous work.openVorabbi, Matteo; Gennari, Michael; Finelli, Paolo; Giusti, Carlotta; Navrátil, Petr; Machleidt, RuprechtVorabbi, Matteo; Gennari, Michael; Finelli, Paolo; Giusti, Carlotta; Navrátil, Petr; Machleidt, Ruprech
Unitary limit and linear scaling of neutrons in harmonic trap with tuned CD-Bonn and square-well interactions
Family of chiral two- plus three-nucleon interactions for accurate nuclear structure studies
We present a family of nucleon-nucleon (NN) plus three-nucleon (3N)
interactions up to N3LO in the chiral expansion that provides an accurate ab
initio description of ground-state energies and charge radii up to the
medium-mass regime with quantified theory uncertainties. Starting from the NN
interactions proposed by Entem, Machleidt and Nosyk, we construct 3N
interactions with consistent chiral order, non-local regulator, and cutoff
value and explore the dependence of nuclear observables over a range of mass
numbers on the 3N low-energy constants. By fixing these constants using the 3-H
and 16-O ground-state energies, we obtain interactions that robustly reproduce
experimental energies and radii for large range from p-shell nuclei to the
nickel isotopic chain and resolve many of the deficiencies of previous
interactions. Based on the order-by-order convergence and the cutoff dependence
of nuclear observables, we assess the uncertainties due the interaction, which
yield a significant contribution to the total theory uncertainty.Comment: 6 pages, 5 figures, 1 tabl