NEW INVARIANTS OF PERIODIC KNOTS

For knots in S-3 We obtain new criteria for periodicity. We show that the Casson-Gordon invariants of a periodic knot are preserved under th e periodic action lifted to the cyclic covers. As an application, we c onsider a family of knots with the Seifert form of a period 3 knot, an d using Casson-Gordon invariants show that knots in this family do not have period 3. We also obtain periodicity criteria in terms of the ho mology groups of cyclic branched covers of S-3.