Early Universe Hypercharge Breaking and Neutrino Mass Generation

Area of Science:

• Particle Physics
• Cosmology
• High-Energy Physics

Background:

• The Standard Model (SM) describes fundamental particles and forces, but does not fully explain neutrino masses or the Universe's matter-antimatter asymmetry.
• Extensions to the SM are proposed to address these shortcomings, often involving new symmetries and particles.
• Radiative neutrino mass generation models offer a mechanism for generating small neutrino masses through loop interactions.

Purpose of the Study:

• To investigate the implications of spontaneous U(1)_Y hypercharge gauge symmetry breaking in the early Universe.
• To explore how such symmetry breaking, within extensions of the SM, can facilitate baryogenesis and explain the matter-antimatter asymmetry.
• To analyze the Zee-Babu radiative neutrino mass model for potential charge-breaking scenarios conducive to early Universe baryogenesis.

Main Methods:

• Theoretical analysis of Standard Model extensions that incorporate radiative neutrino mass generation.
• Focus on scenarios with spontaneous breaking of the U(1)_Y hypercharge symmetry at high temperatures.
• Examination of the Zee-Babu model to identify conditions for charge-breaking lepton masses prior to electroweak symmetry breaking.

Main Results:

• Conditions for spontaneous U(1)_Y hypercharge symmetry breaking are generically present in SM extensions that generate light neutrino masses radiatively.
• Early Universe hypercharge breaking opens new avenues for explaining the observed matter-antimatter asymmetry.
• In the Zee-Babu model, a period of hypercharge breaking can enable successful baryogenesis via a novel leptogenesis mechanism involving charge-breaking lepton masses.

Conclusions:

• Spontaneous hypercharge symmetry breaking in the early Universe is a viable scenario within certain Standard Model extensions.
• This symmetry breaking provides a compelling framework for non-conventional leptogenesis, potentially explaining the matter-antimatter asymmetry.
• The Zee-Babu model serves as a concrete example where these conditions can be met, linking neutrino physics to cosmology.