New Perspectives on Bound States and the Flavor Problem

Arizona State University, Scottsdale AZ

Investigators

Abstract

With the progress of science, the previously distinct disciplines of nuclear physics, elementary particle physics, astrophysics, and cosmology are becoming ever more closely intertwined. This award, while nominally categorized under nuclear theory because of its focus on the structure and dynamics of subnuclear particles, also contains strong elements of particle theory, atomic physics, and even string theory. In order to reflect not only the wide interests of the PI and co-PI, but also to provide their Ph.D. students a wide range of exciting research opportunities, the project covers five distinct areas of study in which rapid progress is attainable. The award also provides some support for short-term visitors (collaborators and seminar speakers), whose expertise will stimulate further advances in the project areas, and travel funds for all personnel to present their findings at seminars and conferences and to learn about new advances in physics. The broader significance of this project is thus incorporated in (i) interdisciplinary research that crosses boundaries between fields, (ii) the training of junior researchers in the methods and findings these disciplines, and (iii) cross-institutional exchanges to maximize the effectiveness of all involved researchers' skills. The five topics are: (1) Baryons, such as protons and neutrons, can be studied by allowing the number of charges (Nc) of the strong nuclear force to vary. The "1/Nc expansion" is based on the idea that the structure and dynamics of baryons are easier to understand if Nc is considered a large number (it is 3 in our universe). But recent work shows that the expansion is not unique. The PI will compare the predictions of different 1/Nc expansions using experimental data to determine which, if any, is preferred. (2) Generalized parton distributions are the most fundamental observable quantities for describing the structure of strongly-interacting particles such as protons. The upgrade at Jefferson Lab in Newport News, Virginia makes it possible to measure them with unprecedented accuracy, so the calculation of corrections to the older "low-order" results by the co-PI will be essential to our determination of whether one really understand what is going on inside a proton. (3) Protons are sensitive not only to the strong nuclear force, but the weak force as well through the process of "electroweak deep inelastic scattering" (EW DIS), and these effects will appear not only in data at Jefferson Lab, but also subsequent facilities. The co-PI will calculate corrections to the lowest-order results, which will allow one to understand how multiparticle states are correlated at long distance and to separate known from as-yet-unknown physics. (4) Both the PI and co-PI will study the origin of how different species of neutrinos, extremely light and electrically neutral particles, can transform into each other. They will employ both conventional symmetry approaches within the context of quantum field theory and string-theoretical approaches based upon the idea that particles arise from structures called "D-branes" that live in extra dimensions of spacetime but intersect with our dimensions. (5) The PI will build on his recent work describing how to create "true muonium" - an atom consisting of a muon (a subatomic particle created, for example, in cosmic rays) and its antiparticle, in immediately realizable experiments. Like all atoms, it appears in a multitude of excited states with a rich spectroscopy, and how to create and characterize these states is interesting not only for its own sake but for precision tests of the electromagnetic forces that bind the true muonium atom.