Infinity cancellation, type I′ compactification and string S-matrix functional Original Research Article

Non-vanishing tadpoles and possible infinities associated in the multiparticle amplitudes are discussed with regard to the disk and RP2 diagrams of the type I′ compactification. We find that the infinity cancellation of the SO(32) type I theory extends to this case as well despite the presence of tadpoles localized in the D-brane world-volume and the orientifold surfaces. Formalism of the string S-matrix generating functional is presented to find a consistent string background as the c-number source function: we find this only treats the cancellation of tadpoles in the linearized approximation. Our formalism automatically provides a representation of the string amplitudes on this background to all orders in α′.