Localized zero modes enhance massive Casimir interactions

Massive quantum fields usually mediate Casimir interactions that are exponentially screened beyond their Compton wavelength. We show that an isolated normalizable zero mode in a classical background opens a low-frequency collective channel that bypasses this screening. The effective interaction is universal, controlled only by the zero-mode profile. Kinks and planar domain walls provide robust realizations, with the sine-Gordon/P\"oschl--Teller kink as an exactly solvable example. Localized zero modes thus define a generic infrared mechanism for modifying massive vacuum forces.