New formulations of D=10 supersymmetry and D8-O8 domain walls

We discuss a generalized form of IIA/IIB supergravity depending on all R-R potentials C-(p) (p = 0, 1,..., 9) as the effective field theory of type IIA/IIB superstring theory. For the IIA case we explicitly break this R-R democracy to either p less than or equal to 3 or p greater than or equal to 5, which allows us to write a new bulk action that can be coupled to N = 1 supersymmetric brane actions. The case of eight-braves is studied in detail using the new bulk & brane action. The supersymmetric negative-tension branes without matter excitations can be viewed as orientifolds in the effective action. These D8-branes and O8-planes are fundamental in type I' string theory. A BPS eight-brave solution is given which satisfies the jump conditions on the wall. It implies a quantization of the mass parameter in string units. Also, we find a maximal distance between the two walls, depending on the string coupling and the mass parameter. We derive the same results via supersymmetric flow equations.