Leptogenesis and a Jarlskog invariant

The relation between low energy CP violating phases, and the CP asymmetry of leptogenesis 1, 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 1 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 1 is related to MNS phases.