Homa M. and Hryniv R., Spectra of PT-symmetric operators under rank-one perturbations // J. Phys. A: Math. Theor. 2020. V. 53 -- paper id 375202 (15pp), https://doi.org/10.1088/1751-8121/aba8d1
Abstract:
We study the spectra of PT-symmetric Hamiltonians H that are rank-one perturbations of a self-adjoint PT-symmetric Hamiltonian H0. We show that the discrete spectrum of H may include any number of complex–conjugate pairs of complex numbers of arbitrary algebraic multiplicity.
