Analytic derivation of an approximate SU(3) symmetry inside the symmetry triangle of the Interacting Boson Approximation model

TL;DR

This paper analytically derives an approximate SU(3) symmetry line within the IBA symmetry triangle, explaining the arc of regularity and providing a novel insight into algebraic model symmetries in nuclear physics.

Contribution

It presents the first analytical derivation of an approximate SU(3) symmetry line inside the IBA symmetry triangle, linking algebraic contraction to regularity in nuclear models.

Findings

Identifies a line of preserved SU(3) symmetry within the IBA triangle.

Explains the arc of regularity connecting SU(3) and U(5) vertices.

Provides a method applicable to algebraic models with subalgebras suitable for contraction.

Abstract

Using the contraction of the SU(3) algebra to the algebra of the rigid rotator in the large boson number limit of the Interacting Boson Approximation (IBA) model, a line is found inside the symmetry triangle of the IBA, along which the SU(3) symmetry is preserved. The line extends from the SU(3) vertex to near the critical line of the first order shape/phase transition separating the spherical and prolate deformed phases, and lies within the Alhassid--Whelan arc of regularity, the unique valley of regularity connecting the SU(3) and U(5) vertices amidst chaotic regions. In addition to providing an explanation for the existence of the arc of regularity, the present line represents the first example of an analytically determined approximate symmetry in the interior of the symmetry triangle of the IBA. The method is applicable to algebraic models possessing subalgebras amenable to contraction. This condition is equivalent to algebras in which the equilibrium ground state (and its rotational band) become energetically isolated from intrinsic excitations, as typified by deformed solutions to the IBA for large numbers of valence nucleons.