# Physics Colloquium

## "Skyrmions and Nuclei"

#### Presented by Nick Manton

Tuesday, November 8, 2016, 3:30 pm — Large Seminar Room, Bldg. 510

Nuclear forces are mediated by pions. As pions are light compared to

nucleons and other mesons, they are treated as approximate Goldstone

bosons in an effective field theory (EFT) with spontaneously broken SO(4) chiral symmetry. Generically, the nonlinear field equations of EFT have topological soliton solutions called Skyrmions, which we identify as the intrinsic structures of nucleons or larger nuclei.

The quantum states of the unit-winding, spherical Skyrmion represent protons and neutrons with spin half. Skyrmions of many higher winding numbers are also known, having beautiful symmetries, and sometimes showing alpha-particle or other clustering. The classical solutions

have definite location, orientation, and pion field orientation,

so we quantize the collective coordinates to obtain states with definite momentum, spin and isospin. A Skyrmion's symmetry restricts its allowed spin/isospin combinations (Finkelstein—Rubinstein constraints). The recent inclusion of vibrational degrees of freedom has helped to create a reasonable model for Oxygen-16 and its excited states.

Hosted by: Robert Pisarski

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