Shadow geometry at singular points of CAT(k) spaces

Abstract

In any CAT(k) space M, the "shadow" of a tangent vector Z at a point p is the set vectors that form an angle of \pi or more with Z. Taking logarithm maps at points approaching p along a fixed geodesic ray from p with tangent Z collapses the shadow to a single ray while leaving isometrically intact every convex cone that avoids the shadow of Z.