Leptogenesis and a Jarlskog Invariant

The relation between low energy CP violating phases, and the CP asymmetry of leptogenesis, $\epsilon$, is investigated. Although it is known that in general those are independent, there may be a relation when a model is specified. We construct a Jarlskog invariant which is proportional to $\epsilon$ if the right-handed neutrino masses are hierarchical. Since the invariant can be expressed in terms of left-handed neutrino parameters--some measurable, and some not--it is useful in identifying the limits in which $\epsilon$ is related to MNS phases.