M. J. Savage

This year has been quite an exciting time for the application of effective field theory to nuclear physics. With our recent development of a consistent power-counting, Beane and I explored the dependence of the two-nucleon systems on the light quark masses, $m_q$. We were able to arrive at an analytic expression for the scattering length in the ${}^1\kern -.14em S_0$ channel as a function of $m_q$, and a numerical formulation for the ${}^3\kern-.14em S_1-{}^3\kern-.14em D_1$ coupled channels. Therefore, for the first time the leading order $m_q$-dependence of the deuteron binding energy and of the di-neutron system were examined. This is clearly the first step in a much bigger program to understand how nuclear physics depends upon the fundamental constants of nature.

Partially-Quenched QCD (PQQCD) is another area where significant progress was made this year. It has been recently realized that lattice simulations of the unphysical theory PQQCD allows for the rigorous determination of QCD quantities. In the meson sector, combinations of Gasser-Leutwyler coeffciients that appear at order $p^4$ in the chiral expansion have been extracted from PQ lattice QCD simulations. Chen, Beane and I extended the PQ theory to include baryons and computed several observables at the one-loop level, including matrix elements of twist-2 operators, masses, magnetic moments and so forth. We also explored the potential between two baryons each containing one heavy quark, in order to learn something about the intermediate range nuclear interaction.