Anomalous collective modes in atomic nuclei within the proton-neutron interacting boson model

TL;DR

This paper identifies novel collective modes with low $B_{4/2}$ ratios in atomic nuclei using the proton-neutron interacting boson model, explaining anomalies in neutron-deficient nuclei and revealing triaxial spectral features.

Contribution

It introduces a new understanding of anomalous $B_{4/2}$ ratios through the IBM-2, linking these modes to triaxiality and band mixing in nuclei.

Findings

Identification of $B_{4/2}<1.0$ modes in IBM-2

Explanation of $B_{4/2}$ suppression in specific isotopes

Connection between modes and triaxial spectral features

Abstract

Novel collective modes characterized by a $B_{4/2}$ ratio ($\equiv B(E2;4_1^+\rightarrow 2_1^+)/B(E2;2_1^+\rightarrow 0_1^+)$) less than 1.0 that were observed recently have been identified within the proton-neutron interacting boson model (IBM-2) using the consistent-$Q$ Hamiltonian. These modes are shown to give rise to triaxial spectral features, including significant band mixing. The results provide a compelling explanation for the deeply suppressed $B_{4/2}$ ratio observed in $^{166}$W, $^{168,170}$Os, and $^{172}$Pt, offering new insights into the $B(E2)$ anomaly phenomenon in neutron-deficient nuclei.