We prove that wave operators of scattering theory for fourth order Schrödinger operators Formula: see text on Formula: see text with real potentials Formula: see text such that Formula: see text and Formula: see text for an Formula: see text, Formula: see text, are bounded in Formula: see text for all Formula: see text if Formula: see text is regular at zero in the sense that there are no non-trivial solutions to Formula: see text such that Formula: see text and if positive eigenvalues are absent from Formula: see text. This reduces Formula: see text-mapping properties of functions Formula: see text of Formula: see text to those of Fourier multipliers Formula: see text.
Galtbayar et al. (Thu,) studied this question.