Theoretical Study of Nucleon Structure and Hadronic Interactions

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It is now understood that neutrons and protons, the constituents of the atomic nucleus, are themselves composed of quarks. A major question in nuclear physics is how this quark substructure is manifested in observables in nuclear physics. To reveal these quark effects, we concentrate on approximate symmetries. These are symmetries of nature that are nearly, but not completely,obeyed. Studying how these symmetries are violated, and by how much, allows us to examine quark effects in nuclear physics. We focus particularly on charge symmetry; this would be an exact symmetry if there were no differences between protons and neutrons. We concentrate on effects of breaking charge symmetry at high energies, where the quark structure of matter is more evident.We also propose to study details of the strong interaction, the interaction that holds the atomic nucleus together. We are currently concentrating on "exclusive" reactions (scattering reactions where all of the final products are observed). We are trying to determine the most efficient of two equivalent ways of describing these reactions. Another area of proposed study is an examination of effects that occur when particles move in extremely small two-dimensional systems. It has long been known that particles like atoms and molecules possess both particle and wave properties. In most cases the "wave" properties of matter are small, subtle effects. In certain systems, the wave effects can dominate observed properties. These effects are seen in "nanoscale"systems (with dimensions roughly those between atoms in a solid) with visible light, or by using microwaves in systems with dimensions in centimeters. We carry out numerical simulations in collaboration with a physicist who conducts experiments on microwave systems. The broader impacts involve training of scientists in high-tech fields. We carry out research with undergraduates, grad students and postdocs, who become expert in complex systems with applications in technology, pure research, defense, communications and finance. Recent postdocs have included several women, and this trains new women scientists. The principal investigator (PI) provides seminars on recent advances in physics for non-scientists; these talks increase scientific literacy in the general population. The PI and his students volunteer for a children's science museum in Bloomington, Indiana. He is currently a participant in a multidisciplinary study of "Science and American Public Democracy" at the Indiana University Poynter Center for Ethics and Public Institutions.