Phase diagram for a Cubic Consistent-Q Interacting Boson Model Hamiltonian: signs of triaxiality

TL;DR

This paper extends the Interacting Boson Model with a cubic quadrupole term, analyzing its phase diagram and revealing that triaxial shapes are rare and transitions are rapid, often making triaxiality hard to detect.

Contribution

It introduces a cubic QxQxQ interaction into the IBM and explores its impact on nuclear shape phase transitions and triaxiality, providing explicit potential energy calculations.

Findings

Triaxiality is very limited in the model.

Prolate to oblate transition is rapid.

Triaxiality may often be unnoticed.

Abstract

An extension of the Consistent-Q formalism for the Interacting Boson Model that includes the cubic QxQxQ term is proposed. The potential energy surface for the cubic quadrupole interaction is explicitly calculated within the coherent state formalism using the complete chi-dependent expression for the quadrupole operator. The Q-cubic term is found to depend on the asymmetry deformation parameter gamma as a linear combination of cos(3gamma) and cos^2(3\gamma) terms, thereby allowing for triaxiality. The phase diagram of the model in the large N limit is explored, it is described the order of the phase transition surfaces that define the phase diagram, and moreover, the possible nuclear equilibrium shapes are established. It is found that, contrary to expectations, there is only a very tiny region of triaxiality in the model, and that the transition from prolate to oblate shapes is so fast that, in most cases, the onset of triaxiality might go unnoticed.