Chiral Hodge cohomology and Mathieu moonshin

We construct a filtration of chiral Hodge cohomolgy of a K3 surface $X$, such that its associated graded object is a unitary representation of the N=4 vertex algebra with central charge $6$ and its subspace of primitive vectors has the property: its equivariant character for a symplectic automorphism $g$ of $X$ agrees with the McKay-Thompson series for $g$ in Mathieu moonshine.