Effective field theory of pairing rotations

TL;DR

This paper develops a model-independent effective theory for pairing rotations in finite superfluid systems, explaining low-energy excitations and their relation to symmetry breaking, with applications to nuclear physics.

Contribution

It provides a novel, symmetry-based derivation of pairing rotations applicable to finite superfluids, including nuclei, and relates them to observable reactions.

Findings

Reproduces pairing rotational band data within uncertainties.

Establishes relations between double charge-exchange reactions and pair transfer.

Describes odd nuclei by coupling a fermion to the superfluid.

Abstract

Pairing rotations are the low-energy excitations of finite superfluid systems, connecting systems that differ in their number of Cooper pairs. This paper presents a model-independent derivation of pairing rotations within an effective theory that exploits the emergent breaking of U(1) phase symmetries. The symmetries are realized nonlinearly and the Nambu-Goldstone modes depend only on time because the system is finite. Semi-magic nuclei exhibit pairing rotational bands while the pairing spectrum becomes an elliptical paraboloid for open-shell nuclei. Model-independent relations between double charge-exchange reactions and alpha particle capture or knockout in open-shell nuclei are in analogy to the pair transfer reactions in a single superfluid. Odd semi-magic nuclei are described by coupling a fermion to the superfluid. The leading-order theories reproduce data for pairing rotational bands within uncertainty estimates.