Abstract
We present a freeze-in realization of the Dirac neutrinogenesis in which the decaying particle that generates the lepton-number asymmetry is in thermal equilibrium. As the right-handed Dirac neutrinos are produced non-thermally, the lepton-number asymmetry is accumulated and partially converted to the baryon-number asymmetry via the rapid sphaleron transitions. The necessary CP-violating condition can be fulfilled by a purely thermal kinetic phase from the wavefunction correction in the lepton-doublet sector, which has been neglected in most leptogenesis-based setup. Furthermore, this condition necessitates a preferred flavor basis in which both the charged-lepton and neutrino Yukawa matrices are non-diagonal. To protect such a proper Yukawa structure from the basis transformations in flavor space prior to the electroweak gauge symmetry breaking, we can resort to a plethora of model buildings aimed at deciphering the non-trivial Yukawa structures. Interestingly, based on the well-known tri-bimaximal mixing with a minimal correction from the charged-lepton or neutrino sector, we find that a simultaneous explanation of the baryon-number asymmetry in the Universe and the low-energy neutrino oscillation observables can be attributed to the mixing angle and the CP-violating phase introduced in the minimal correction.
Highlights
(SM); e.g., the SM predicts an electron Yukawa coupling with ye 10−6
The feebleness stirs up a new leptogenesis, named Dirac neutrinogenesis (DN) [3], in which the out-of-equilibrium condition for generating the lepton-number (L) asymmetry can be guaranteed and the baryon-number (B) asymmetry is generated via thermal sphaleron transitions [4], even in a theory with B−L = 0 initially
It has been illustrated in Ref. [10] and later implemented in Ref. [16] that, at high-temperature regime where thermal effects come into play, the zero-temperature cutting rules should be superseded by the thermal cuts [17], allowing nonzero contributions to the leptonic CP asymmetry that would otherwise vanish at the vacuum regime
Summary
In the typical versions of DN mechanism [3,5,6,7,8,9], the lepton-number asymmetry is generated by heavy particle decays with a non-thermal distribution. As will be exploited in this paper, when both thermal effects and nontrivial mixings in the charged-lepton and neutrino sectors are taken into account, one can expect the leptonic CP asymmetry at finite temperature to carry a nonzero imaginary piece, i.e., Im[(YνYν†)(Y Y †)] = 0, where Y and Yν denote respectively the charged-lepton and neutrino Yukawa matrices that are responsible for their respective masses and mixings. This enables us to exploit a direct interplay between the BAU and the neutrino oscillation observables in a minimal setup, without tuning additional Yukawa couplings beyond Y ,ν.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call