Perfectly invisible PT $$ \mathcal{P}\mathcal{T} $$ -symmetric zero-gap systems, conformal field theoretical kinks, and exotic nonlinear supersymmetry

Abstract We investigate a special class of the PT $$ \mathcal{P}\mathcal{T} $$ -symmetric quantum models being perfectly invisible zero-gap systems with a unique bound state at the very edge of continuous spectrum of scattering states. The family includes the PT $$ \mathcal{P}\mathcal{T} $$ -regularized two particle Calogero systems (conformal quantum mechanics models of de Alfaro-Fubini-Furlan) and their rational extensions whose potentials satisfy equations of the KdV hierarchy and exhibit, particularly, a behaviour typical for extreme waves. We show that the two simplest Hamiltonians from the Calogero subfamily determine the fluctuation spectra around the PT $$ \mathcal{P}\mathcal{T} $$-regularized kinks arising as traveling waves in the field-theoretical Liouville and SU(3) conformal Toda systems. Peculiar properties of the quantum systems are reflected in the associated exotic nonlinear supersymmetry in the unbroken or partially broken phases. The conventional N=2 $$ \mathcal{N}=2 $$ supersymmetry is extended here to the N=4 $$ \mathcal{N}=4 $$ nonlinear supersymmetry that involves two bosonic generators composed from Lax-Novikov integrals of the subsystems, one of which is the central charge of the superalgebra. Jordan states are shown to play an essential role in the construction