CP Violation in Seesaw Model

We study the structure of CP violating phases in the seesaw model. We find that the $3\times 6$ MNS matrix contains six independent phases, three of which are identified as a Dirac phase and two Majorana phases in the light neutrino sector while the remaining three arise from the mixing of the light neutrinos and heavy neutrinos. We show how to determine these phases from physical observables.