Resonance enhancement of the electromagnetic interaction between two charged particles in the bound state in the continuum

Abstract

In bound states in the continuum (BIC) the mass of a composite particle is greater than the total mass of its constituents. The BIC state is investigated in a system of two charged particles [Formula: see text] and [Formula: see text] with different masses ([Formula: see text]), using the ladder Bethe–Salpeter equation. We demonstrate that there are two momentum space regions for the positive binding energy, in which the electromagnetic interaction between the particles is strongly enhanced, and the effective coupling constant turns out to be equal to [Formula: see text], where [Formula: see text] is the fine structure constant. The interaction resonance confines the constituents in the BIC state with the positive binding energy, which is of the order of the mass of the lighter particle from this pair.