Three-Nucleon Interactions from Few- to Many-Body Systems

March 12 - 16, 2007

Questions for the TRIUMF 3N Workshop

DEFINITION ``THREE-NUCLEON FORCE'' 3NF (conservative, ad hoc): A force whose contribution only affects observables in processes involving three or more nucleons. By iteration, a 4NF is one which contributes only to observables involving four or more nucleons, etc. This definition focuses on observable, model-independent 3NF effects only. NN off-shell effects and point-like 3NFs are therefore both examples of 3NFs.

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FORMALISM/SCHEME DEPENDENCE: How are 3NFs implemented in different formalisms? How to relate 3NFs between different schemes?

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OBSERVATION: It is imperative to document the global impact of 3NFs in experiment. How can we constrain its space, spin, and isospin dependence from data? Given scarce resources in both theory and experiment, which experiments are most crucial? Is a 3N phase-shift analysis desirable and possible with the present data?

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NORMALISATION CONDITIONS: What data should be used to determine 3NF parameters? How are normalisation conditions involving light nuclei, p-d scattering, NN or \pi-N systems related? Can it be advantageous to constrain 3NF parameters in medium-mass nuclei or nuclear matter?

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A_y PROBLEM: Are there 3NFs that solve the A_y problem? Can
modifications/corrections of NN observables solve A_y? If so, are they consistent with NN data?

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ISOSPIN DEPENDENCE: 3NFs are important for neutron-rich nuclei. How can radioactive beam facilities (ISAC, RIA, FAIR,...) explore 3NFs? Can we gain information on their isospin 3/2-component from photo- or electro-induced processes, p-3He, n-3H scattering or nuclear reactions?

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CHIRAL EFT: What is the relation between NN and many-N forces? How sensitive are observables to changes in the low-energy coefficients c_i? Can fits to NN/pi-N data determine these parameters? What other low-energy coefficients do we need to determine? What evidence do we have that the power-counting is working? Do we need to include explicit Delta(1232)s? Up to what density do we expect the expansion in NN, 3N, 4N,... forces to work?

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HALO NUCLEI: What is the universal physics in halo nuclei and nuclear reactions with large scattering lengths? Can we derive correlation lines similar to the Phillips and Tjon lines for halo nuclei? Under which circumstances can we interpret deviations from such lines as 3NFs?

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MEDIUM-MASS AND HEAVY NUCLEI: What is the global impact of 3NFs on nuclear structure? What is the role of 3NFs in spin-orbit splittings and nuclear saturation?

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DENSE MATTER AND ASTROPHYSICS: Which role do 3NFs play in astrophysics and dense matter? What is the error due to neglected 3NFs and higher-body interactions, e.g. in BBN and Supernovae/Neutron Stars?

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P-D SCATTERING AT INTERMEDIATE ENERGIES: Many p-d spin observables show evidence of 3NF effects. However, the record of present 3NF calculations in explaining the data is mixed. How can we improve 3NFs (and consistent NN interactions)?

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How can 3NF parameters be extracted from LATTICE QCD? How far away are such calculations?

Community Questions

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HOW TO BUILD A 3NF THEORY INFRASTRUCTURE?: 3NF calculations are usually technically quite difficult. How can we develop infrastructure to help with these calculations? Please consider contributing your code, expertise, or assistance to advance calculations with 3NFs.

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HOW TO MAINTAIN THE 3NF EXPERIMENTAL INFRASTRUCTURE?: Labs capable of collecting few-N data at low and intermediate energies seem to disappear at a time when theory finally makes reliable, high-accuracy calculations. How can we convey the unique opportunities and sense of urgency?

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COMMUNITY SUPPORT: Many 3NF projects are long. How can the 3NF community support you, your grant application, your experiment, your accelerator?

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How should we FOLLOW UP this 3NF workshop? What should we do to make further progress? Hold another workshop in two(?) years? Hold an INT or ECT* 3NF program? Form an explicit 3NF collaboration? Or a p-d scattering partial-wave analysis collaboration? Other initiatives?