Leptogenesis and Dirac neutrino masses in SO(10)

TL;DR

This paper explores how Dirac neutrino masses within SO(10) GUTs influence leptogenesis and baryon asymmetry, showing that relaxing certain mass relations allows for realistic neutrino spectra and baryon asymmetry consistent with observations.

Contribution

It demonstrates that including multiple Higgs representations in SO(10) models relaxes mass constraints and yields viable neutrino spectra and baryon asymmetry predictions.

Findings

Heavy neutrino masses are consistent with SO(10) unification scale.

Predicted baryon asymmetry matches observational data.

Relaxed mass relations enable realistic leptogenesis scenarios.

Abstract

Within the scheme of Baryogenesis through Leptogenesis in the single flavor approximation, we emphasize the role of the Dirac neutrino mass $m_D$ in the SO(10) Grand Unification scheme, using the Higgs representations for the fermions masses ${\bf 10}$ and $\overline{\bf 126}$. Both representations are needed to get relations among the fermion masses, e.g. $m_b = m_\tau$, $m_\mu = 3 m_s$,... Taking these two representations allow to relax the condition $m_D = m_u$ obtained with the representation ${\bf 10}$ alone and to have general Dirac masses $m_D \not = m_u$. On the other hand, we assume that the antisymmetric representation ${\bf 120}$ is absent. Within this hypothesis, the unitary matrices $V^L$ and $V^R$ that diagonalize $m_D$ through $m_D = V^{L \dagger} m_D^{diag} V^R$ still satisfy the relation $V^R = V^{L*}$. Under these conditions, unlike the case of keeping only the ${\bf 10}$ representation, we obtain in parameter space several examples of the heavy neutrino spectrum consistent with the SO(10) unification scale, and a value for the baryon asymmetry $Y_B$ in agreement with data. For illustration, we detail a case that gives the heavy spectrum with masses $M_1 = 6.26 \times 10^{10}\ {\rm GeV}$, $M_2 = 2.23 \times 10^{12}\ {\rm GeV}$, $M_3 = 4.57 \times 10^{14}\ {\rm GeV}$ and, in the strong washout regime, the baryon asymmetry $Y_B = 8.50 \times 10^{-11}$ consistent with the data.