A note on superconformal N = 2 theories and orientifolds

We construct the T-duals of certain type IIA brane configurations with one compact dimension (elliptic models) which contain orientifold planes. These configurations realize four-dimensional N = 2 finite field theories. For e lliptic models with two negatively charged orientifold six-planes, the T-du als are given by D3-branes at singularities in the presence of O7-planes an d D7-branes. For elliptic models with two oppositely charged orientifold pl anes, the T-duals are D3-branes at a different kind of orientifold singular ities, which do not require D7-branes. We construct the adequate orientifol d groups, and show that the cancellation of twisted tadpoles is equivalent to the finiteness of the corresponding field theory. One family of models c ontains orthogonal and symplectic gauge factors at the same time. These new orientifolds can also be used to define some six-dimensional RG fixed poin ts which have been discussed from the type IIA brane configuration perspect ive. (C) 1999 Elsevier Science B.V.