Department of Physics Calendar
Physics Colloquium – Ragnar Stroberg
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Title: A Modern Makeover for the Shell Model
Abstract: The shell model has been the workhorse of nuclear structure theory for decades, providing both accurate predictions and a framework for interpreting experiments. The main drawback of the shell model has been the need for (semi-) phenomenological adjustments of its parameters. These adjustments obscure the connection to the underlying interaction between nucleons and introduce ambiguities in e.g. the consistent treatment of nuclear reactions, or predictions of how new physics beyond the Standard Model (BSM) would manifest in nuclear observables. The adjustments also can cause trouble when extrapolating from stable nuclei, (where the adjustments are fit) to the very exotic nuclei produced in astrophysical events and the upcoming Facility for Rare Isotope Beams.
I will discuss recent progress in using a renormalization group approach to derive shell-model parameters from the underlying interaction without the need for phenomenological adjustments. In addition, the development of chiral effective field theory allows for a consistent and systematically improvable framework for nuclear forces and electroweak (or BSM) physics. In particular, I will argue that three-nucleon forces provide an explanation of the historically needed phenomenological adjustments.
Finally, I will present two recent applications of this approach: a prediction of the limits of the nuclear chart from helium (Z=2) to calcium (Z=20), and a treatment of the long-standing “gA quenching” problem in nuclear beta decays.