Spatial degeneracy along weak geodesics in the space of Kähler potentials

Abstract

We study spatial Hessian degeneracy along weak Kähler geodesics. We construct examples in three settings: (1) On every compact Kähler manifold, the spatial form degenerates on a nonempty open set during an interior time interval, although both endpoints are smooth and strictly Kähler. (2) On ALE Kähler manifolds with a holomorphic quotient end and a decaying potential to the Euclidean metric, spatial degeneracy occurs on open regions arbitrarily far along an unbounded horn. (3) For cone and Poincaré endpoint metrics along a smooth divisor, normal spatial degeneracy occurs on open sets approaching the divisor. Both cone endpoints retain the prescribed angle. The first construction answers negatively the spatial-positivity question recorded in Darvas's survey. The ALE and divisor constructions show that weak geodesics need not preserve the asymptotic behavior of the endpoint metrics.