  We present a theory of magnonic thermal Hall transport driven by many-body
skew scattering. In field-polarized chiral magnets, the Dzyaloshinskii-Moriya
interaction induces three-magnon interactions that violate time-reversal
symmetry and interfere with the four-magnon scattering, thereby breaking
microscopic detailed balance and causing thermal Hall currents. This mechanism
operates without disorder or Berry curvature and is intrinsic to interacting
spin systems. We argue that it can be as significant as the band-geometric
anomalous velocity, highlighting the importance of magnon correlations in
thermal Hall physics.
