Weak Fan Structures for Two-Parameter Degenerations of K3 Surfaces

Abstract: In this note, we provide an explicit computation of the weak fan associated with a two-parameter degeneration of K3 surfaces. This example serves as a concrete illustration of the general framework developed by Robles and Deng (2023) for the compactification of period maps via nilpotent orbits in the non-Hermitian case. We describe the associated nilpotent cones, examine their compatibility conditions, and construct the weak fan governing the degeneration behavior. This computation contributes to the broader understanding of boundary components of period domains and their relation to limiting mixed Hodge structures.