Search for the Double Poles of the Scattering Matrix in Light Nuclei
arXiv:2607.11453 · doi:10.1103/ykjr-796z
The authors use the coupled‑channel Gamow Shell Model to locate exceptional points—double poles of the scattering matrix—in light nuclei (⁶Li, ⁷Li, ⁷Be, ⁸Be) and examine how these non‑Hermitian degeneracies affect energies, widths, cross sections and other observables.
Abstract
Exceptional points (EPs) are non-Hermitian degeneracies at which two eigenvalues and their eigenvectors coalesce, producing a defective Hamiltonian and a double pole of the -matrix. Using the coupled-channel Gamow Shell Model with the spin-orbit strengths as control parameters, we locate and characterize EPs in , , , and , and analyze their imprint on energies, widths, phase rigidity, spectroscopic factors, elastic cross sections, survival probabilities, and spectral functions. The signatures of the EP in scattering and time-domain observables are found to be strongly channel-dependent, and threshold effects play a decisive role in determining the accessibility of the EP in parameter space.