Geometry of spaces of orthogonally additive polynomials on C(K)

We study the space of orthogonally additive n-homogeneous polynomials on C(K). There are two natural norms on this space. First, there is the usual supremum norm of uniform convergence on the closed unit ball. As every orthogonally additive n-homogeneous polynomial is regular with respect to the Banach lattice structure, there is also the regular norm. These norms are equivalent, but have significantly different geometric properties. We characterise the extreme points of the unit ball for both norms, with different results for even and odd degrees. As an application, we prove a Banach–Stone theorem. We conclude with a classification of the exposed points.