Surfaces of minimal degree of tame representation type and mutations of Cohen–Macaulay modules

Abstract : We provide two examples of smooth projective surfaces of tame CM type, by showing that the parameter space of isomorphism classes of indecomposable ACM bundles with fixed rank and determinant on a rational quartic scroll in IP5 is either a single point or a projective line. These turn out to be the only smooth projective ACM varieties of tame CM type besides elliptic curves, [1]. For surfaces of minimal degree and wild CM type, we classify rigid Ulrich bundles as Fibonacci extensions. For IF0 and IF1, embedded as quintic or sextic scrolls, a complete classification of rigid ACM bundles is given.