Double pole $S$-matrix singularity in the continuum of $^7$Be

TL;DR

This paper identifies a double pole singularity, known as an exceptional point, in the $^{7}$Be spectrum using the Gamow shell model, revealing coalescence of resonances and singular behaviors in physical quantities.

Contribution

It demonstrates the existence of an exceptional point in $^{7}$Be's resonant spectrum within the Gamow shell model framework, showing coalescence phenomena.

Findings

Coalescence of wave functions and spectral functions at the exceptional point

Singular behavior of spectroscopic factors and electromagnetic transitions

Identification of the double pole $S$-matrix singularity in $^{7}$Be

Abstract

The double pole singularity of the $S$-matrix, the so-called exceptional point, associated with the $5/2^-$ doublet of resonances in the spectrum of $^{7}$Be has been identified in the framework of the Gamow shell model. The exceptional point singularity is demonstrated by the coalescence of wave functions and spectral functions of the two resonances, as well as by the singular behavior of spectroscopic factors and electromagnetic transitions.