Quantal rotation and its coupling to intrinsic motion in nuclei

TL;DR

This paper explores the coupling between rotational and intrinsic motions in nuclei, using a microscopic approach to understand symmetry breaking, collective vibrations, and phenomena like wobbling modes at high spins.

Contribution

It introduces a quantization of the cranking model and analyzes the interplay of rotation and intrinsic motion in nuclei, including the emergence of new soft modes and wobbling excitations.

Findings

Coupling effects are observable in generalized intensity relations at low spin.

A microscopic quantization approach to the cranking model is feasible.

Wobbling modes are identified as signatures of triviality in nuclear excitations.

Abstract

Symmetry breaking is an importance concept in nuclear physics and other fields of physics. Self-consistent coupling between the mean-field potential and the single-particle motion is a key ingredient in the unified model of Bohr and Mottelson, which could lead to a deformed nucleus as a consequence of spontaneous breaking of the rotational symmetry. Some remarks on the finite-size quantum effects are given. In finite nuclei, the deformation inevitably introduces the rotation as a symmetry-restoring collective motion (Anderson-Nambu-Goldstone mode), and the rotation affects the intrinsic motion. In order to investigate the interplay between the rotational and intrinsic motions in a variety of collective phenomena, we use the cranking prescription together with the quasiparticle random phase approximation. At low spin, the coupling effect can be seen in the generalized intensity relation. A feasible quantization of the cranking model is presented, which provides a microscopic approach to the higher-order intensity relation. At high spin, the semiclassical cranking prescription works well. We discuss properties of collective vibrational motions under rapid rotation and/or large deformation. The superdeformed shell structure plays a key role in emergence of a new soft mode which could lead to instability toward the $K^\pi=1^-$ octupole shape. A wobbling mode of excitation, which is a clear signature of the triviality, is discussed in terms of a microscopic point of view. A crucial role played by the quasiparticle alignment is presented.