Integrability of generalised type II defects in affine Toda field theory

The Liouville integrability of the generalised type II defects is investigated. Full integrability is not considered, only the existence of an infinite number of conserved quantities associated with a system containing a defect. For defects in affine Toda field theories (ATFTs) it is shown that momentum conservation is very likely to be a necessary condition for integrability. The defect Lax matrices which guarantee zero curvature, and so an infinite number of conserved quantities, are calculated for the momentum conserving Tzitz\'eica defect and the momentum conserving $D_4$ ATFT defect. Some additional calculations pertaining to the $D_4$ defect are also carried out to find a more complete set of defect potentials than has appeared previously.