Leptogenesis and Neutrino Oscillations in the Classically Conformal Standard Model with the Higgs Portal

TL;DR

This paper explores a classically conformal Standard Model with a Higgs portal that naturally explains electroweak symmetry breaking, neutrino masses, and baryon asymmetry through leptogenesis without explicit mass scales.

Contribution

It demonstrates how scale-invariant models with Coleman-Weinberg mechanisms can generate neutrino masses and baryon asymmetry without fine-tuning or explicit mass parameters.

Findings

Successful leptogenesis via sterile neutrino oscillations

Generation of neutrino masses through the see-saw mechanism

Natural explanation for electroweak scale via radiative symmetry breaking

Abstract

The Standard Model with an added Higgs portal interaction and no explicit mass terms is a classically scale-invariant theory. In this case the scale of electroweak symmetry breaking can be induced radiatively by the Coleman-Weinberg mechanism operational in a hidden sector, and then transmitted to the Standard Model through the Higgs portal. The smallness of the generated values for the Higgs vev and mass, compared to the UV cutoff of our classically scale-invariant effective theory, is naturally explained by this mechanism. We show how these classically conformal models can generate the baryon asymmetry of the Universe without the need of introducing mass scales by hand or their resonant fine-tuning. The minimal model we consider is the Standard Model coupled to the Coleman-Weinberg scalar field charged under the $U(1)_{B-L}$ gauge group. Anomaly cancellation requires automatic inclusion of three generations of right-handed neutrinos. Their GeV-scale Majorana masses are induced by the Coleman-Weinberg field and lead to the generation of active neutrino masses through the standard see-saw mechanism. Leptogenesis occurs via flavour oscillations of right-handed sterile neutrinos and is converted to the baryon asymmetry by electroweak sphalerons.