“…Recent seminal work exposes the fundamental algebraic attributes of these spaces [Mc, KZ, Mö, EMM, EMa, Fil]. Furthermore, the condition of the existence of a holomorphic or meromorphic one-form of fixed signature has been used previously both explicitly and under many guises to obtain divisor classes [Cu,D,C,CC1,L,Mü,GZ,F2,FV] and in lower genus, higher codimension cycles [CC2,CT,Bl] in M g and M g,n . In contrast, conditions from k-differentials for k ≥ 2 have remained an untapped source for effective cycles and questions of the relation of these strata to the birational geometry of M g,n have remained largely unexamined.…”