Electron-deuteron scattering in a relativistic theory of hadrons

We review a three-dimensional formalism that provides a systematic way to include relativistic effects including relativistic kinematics, the effects of negative-energy states, and the boosts of the two-body system in calculations of two-body bound-states. We then explain how to construct a conserved current within this relativistic three-dimensional approach. This general theoretical framework is specifically applied to electron-deuteron scattering both in impulse approximation and when the $\rho \pi \gamma$ meson-exchange current is included. The experimentally-measured quantities $A$, $B$, and $T_{20}$ are calculated over the kinematic range that is probed in Jefferson Lab experiments. The role of both negative-energy states and meson retardation appears to be small in the region of interest.Comment: 17 pages, 4 figures, uses BoxedEPS.tex, lamuphys.sty, bibnorm.sty. To appear in the proceedings of the Workshop on Electron-Nucleus Scattering held at the Elba International Physics Center, June 199

Recent results in chiral effective field theory for the NN system

I describe recent progress towards a theory of the NN force which captures the consequences of QCD's chiral symmetry and the pattern of its breaking, and is formulated as an expansion in a ratio of low and high mass scales, M_{lo}/M_{hi}. This "chiral effective field theory" of the NN system is a firm foundation for explorations of nuclear structure and reactions that are grounded in QCD's low-energy symmetries. While calculations that use a ChiPT expansion for the NN potential have proven very successful, they can only be used with a narrow range of momentum-space cutoffs, which leaves the expansion parameter for observable quantities somewhat murky. Here we seek a truly systematic effective field theory for the NN amplitude, that is manifestly renormalization-group invariant at each order in a demonstrably perturbative expansion.Comment: Invited talk at the 7th International Workshop on Chiral Dynamics, August 6-10, 2012, Jefferson Lab, Newport News, VA. To appear in the proceedings. 12 pages, 5 figure

Three-nucleon forces in the 1/Nc expansion

The operator structures that can contribute to three-nucleon forces are classified in the 1/Nc expansion. At leading order in 1/Nc a spin-flavor independent term is present, as are the spin-flavor structures associated with the Fujita-Miyazawa three-nucleon force. Modern phenomenological three-nucleon forces are thus consistent with this O(Nc) leading force, corrections to which are suppressed by a power series in 1/Nc^2. A complete basis of operators for the three-nucleon force, including all independent momentum structures, is given explicitly up to next-to-leading order in the 1/Nc expansion.Comment: 35 pages, 1 figur

Constraining the neutron-neutron scattering length with \eftnopi

We compute a model-independent correlation between the difference of neutron-neutron and proton-proton scattering lengths |a(nn)-a^C(pp)| and the splitting in binding energies between Helium-3 and tritium nuclei. We use the effective field theory without explicit pions to show that this correlation relies only on the existence of large scattering lengths in the NN system. Our leading-order calculation, taken together with experimental values for binding energies and a^C(pp), yields a(nn)=-22.9 \pm 4.1 fm.Comment: 28 pages, 6 figures, 2 table

The nucleon-nucleon system in chiral effective theory

I discuss the conditions under which the application of chiral perturbation theory to the NN potential gives reliable results for NN scattering phase shifts. ChiPT also yields a convergent expansion for the deuteron charge operator. For cutoffs < 1 GeV, this produces precise predictions for deuterium's quadrupole and charge form factors in the range Q^2 < 0.25 GeV^2.Comment: 4 pages, 4 figures. Contribution to Proceedings of "12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon", Williamsburg, VA, May 31-June 4, 201

The longitudinal response function of the deuteron in chiral effective field theory

We use chiral effective field theory (EFT) to make predictions for the longitudinal electromagnetic response function of the deuteron, f_L, which is measured in d(e,e'N) reactions. In this case the impulse approximation gives the full chiral EFT result up to corrections that are of O(P^4) relative to leading. By varying the cutoff in the chiral EFT calculations between 0.6 and 1 GeV we conclude that the calculation is accurate to better than 10 % for values of q^2 within 4 fm^{-2} of the quasi-free peak, up to final-state energies E_{np}=60 MeV. In these regions chiral EFT is in reasonable agreement with predictions for f_L obtained using the Bonn potential. We also find good agreement with existing experimental data on f_L, albeit in a more restricted kinematic domain.Comment: 33 pages, 10 figures. Accepted for publication in EPJA, with a few further correction