Three-Flavoured Thermal Leptogenesis Without Tuning

@misc{spalding2026threeflavoured,
  title = {{Three-Flavoured Thermal Leptogenesis Without Tuning}},
  author = {Angus Spalding},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.24990},
  eprint = {2609.24990},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.24990},
}

TY  - UNPB
TI  - Three-Flavoured Thermal Leptogenesis Without Tuning
AU  - Angus Spalding
PY  - 2026
DA  - 2026/09/21
PB  - arXiv
DO  - 10.48550/arxiv.2609.24990
UR  - https://arxiv.org/abs/2609.24990
AB  - We investigate thermal leptogenesis in an extension of the Type-I seesaw in which a real singlet scalar couples non-diagonally to the right-handed neutrinos. The interactions −y_ijϕN_iN_j, with i≠ j, introduce new sources of CP violation in heavy-neutrino decays with a negligible enhancement of the standard leptonic washout. We derive an analytic upper bound on the scalar-induced CP asymmetry and present numerical results using fully flavoured Boltzmann equations and the density-matrix formalism. We show that the observed baryon asymmetry can be generated with a hierarchical right-handed-neutrino spectrum at the electroweak scale. In the minimal Type-I seesaw, lowering the scale of decay leptogenesis typically requires either a tuned quasi-degeneracy of the right-handed-neutrino masses or cancellations between the tree-level and one-loop contributions to the light-neutrino masses, while hierarchical leptogenesis instead requires a high scale that aggravates the Higgs hierarchy problem. This singlet-scalar extension appears to avoid these tensions, allowing successful leptogenesis with a hierarchical right-handed-neutrino spectrum down to the electroweak scale.
ER  -