Probing High Scale Dirac Leptogenesis via Gravitational Waves from Domain Walls

Understand

We propose a novel way of probing high scale Dirac leptogenesis, a viable alternative to canonical leptogenesis scenario where the total lepton number is conserved, keeping light standard model (SM) neutrinos purely Dirac.

• The simplest possible seesaw mechanism for generating light Dirac neutrinos involve heavy singlet Dirac fermions and a singlet scalar.
• In addition to unbroken global lepton number, a discrete $Z_2$ symmetry is imposed to forbid direct coupling between right and left chiral parts of light Dirac neutrino.
• Generating light Dirac neutrino mass requires the singlet scalar to acquire a vacuum expectation value (VEV) that also breaks the $Z_2$ symmetry, leading to formation of domain walls in the early universe.