We revisit the generation of a matter-antimatter asymmetry in the minimal
extension of the Standard Model with two singlet heavy neutral leptons (HNL)
that can explain neutrino masses. We derive an accurate analytical
approximation to the solution of the complete linearized set of kinetic
equations, which exposes the non-trivial parameter dependencies in the form of
parameterization-independent CP invariants. The identification of various
washout regimes relevant in different regions of parameter space sheds light on
the relevance of the mass corrections in the interaction rates and clarifies
the correlations of baryogenesis with other observables. In particular, by
requiring that the measured baryon asymmetry is reproduced, we derive robust
upper or lower bounds on the HNL mixings depending on their masses, and
constraints on their flavour structure, as well as on the CP-violating phases
of the PMNS mixing matrix, and the amplitude of neutrinoless double-beta decay.
We also find certain correlations between low and high scale CP phases.
Especially emphasizing the testable part of the parameter space we demonstrate
that our findings are in very good agreement with numerical results. The
methods developed in this work can help in exploring more complex scenarios.
Comment: 54 pages, 18 figures
Subjects: High Energy Physics - Phenomenology; Astrophysics - Cosmology and Nongalactic Astrophysics