  We classify finite energy harmonic 2-forms on the asymptotically flat
gravitational instanton constructed by Chen and Teo. We prove that every
$U(1)$-bundle admits a unique anti-self-dual Yang-Mills instanton (up to gauge
equivalence) which we describe explicitly in coordinates. As an application, we
compute the classical partition function for Maxwell theory with theta term.

Differential Geometry;General Relativity and Quantum Cosmology