  The nature of neutrino masses and the matter-antimatter asymmetry of our
universe are two of the most important open problems in particle physics today
and are notoriously difficult to test with current technology. Dirac neutrinos
offer a solution through a leptogenesis mechanism that hinges on the smallness
of neutrino masses and resultant non-thermalization of the right-handed
neutrino partners in the early universe. We thoroughly explore possible
realizations of this Dirac leptogenesis idea, revealing new windows for highly
efficient asymmetry generation. In many of them, the number of relativistic
degrees of freedom, $N_\text{eff}$, is severely enhanced compared to standard
cosmology and offers a novel handle to constrain Dirac leptogenesis with
upcoming measurements of the cosmic microwave background. Realizations
involving leptoquarks even allow for low-scale post-sphaleron baryogenesis and
predict proton decay. These novel aspects render Dirac leptogenesis
surprisingly testable.
