Affleck-Dine Leptoflavorgenesis

Abstract

We propose a scenario to produce large primordial lepton flavor asymmetries with vanishing total lepton asymmetry, based on the Affleck-Dine mechanism with Q-ball formation. This scenario can produce large lepton flavor asymmetries while automatically maintaining the vanishing total lepton number without fine-tuning, evading the current BBN and the CMB constraints by neutrino oscillations at MeV temperature. The asymmetries can be produced at cosmic temperatures of $T\gtrsim 1\ {\rm GeV}$, early enough to have broad impacts from the early Universe to the present cosmology. This scenario could affect various aspects of early Universe cosmology simultaneously or separately: (i) explaining the observed baryon asymmetry by the same origin as the lepton flavor asymmetries, (ii) affecting the nature of the QCD transition, (iii) opening up a new parameter space of sterile neutrino dark matter by enhancing their production, and (iv) altering the abundance of the light elements, in particular, resolving the recently reported helium-4 anomaly.

Figures (1)

• Figure 1: Typical magnitude of lepton flavor asymmetries, $|Y_L|$, with zero total lepton asymmetry in the Affleck-Dine leptoflavorgenesis. The left (right) panel shows the case with (without) tau flavor asymmetry since the resultant baryon asymmetry depends on the existence of tau flavor asymmetry (cf. Eq. \ref{['eq:YB_vs_YLa']}). We set the flavor ratio $|\kappa_\tau|=1$ with $\sum_\alpha \kappa_\alpha=0$ and $Y_L=Y_{L_\tau}$ (left), $\kappa_e=-\kappa_\mu=1,~ \kappa_\tau=0$ and $Y_L=Y_{L_\mu}$ (right), $m_\phi=10^4~{\rm GeV}$, $\delta_{\rm CP}\lambda=0.1,~|\phi_0|= {M_{\rm P}}$, $\widehat{\beta}=\widehat{\zeta}=\widehat{N}=1$ and the reheating temperature $T_R=10^5~{\rm GeV}$ (cf. Appendix \ref{['app:list_of_paras']}). The blue solid, dashed, dot-dashed lines correspond to $Y_L=10^{-1},~10^{-2}$ and $10^{-3}$, respectively. In the light green region, the Q-ball decay temperature is $T_D\leq1~{\rm GeV}$. For $T_D\gtrsim1~{\rm GeV}$, lepton flavor asymmetries would be generated early enough to affect the QCD transition Asakawa:1989bqSchwarz:2009iiMiddeldorf-Wygas:2020glxVovchenko:2020crkGao:2021nwzFerreira:2025zeuFormaggio:2025nde and the production of sterile neutrino dark matter Akita:2025txo. In the dark green region, $T_D\lesssim 10~{\rm MeV}$, lepton asymmetries are generated after the onset of neutrino oscillations Domcke:2025lzg, which may not be sufficiently washed out and may be inconsistent with the BBN observation. In the light blue region, the baryon asymmetry is overproduced, $|Y_B|\geq10^{-10}$. On the contour of the light blue region, the observed baryon asymmetry can be explained if the tau (mu) flavor asymmetry has a sign opposite to that of the observed baryon asymmetry in the left (right) panels (cf. Eq. \ref{['eq:YB_vs_YLa']}). In the gray region, gravitinos are overproduced compared to the observed dark matter abundance, $\Omega_{\rm 3/2}>\Omega_{\rm DM}$.