Connecting Flavor and Baryon Asymmetry via Leptogenesis in Effective Froggatt-Nielsen Theory

Abstract

We investigate the hierarchical flavor structure of the Standard Model in a Froggatt-Nielsen (FN) framework, where the spontaneous breaking of a $U(1)_{\rm FN}$ symmetry by a complex flavon field generates fermion masses and mixing patterns through higher-dimensional operators. Extending the setup with three right-handed neutrinos (RHNs), light neutrino masses arise via the Type-I seesaw mechanism. Allowing complex FN coefficients enables a consistent description of the CKM and PMNS matrices while inducing CP-violating signatures in meson decays. Building on our previous work, where the lightest RHN acts as a viable dark matter (DM) candidate produced through freeze-in or freeze-out mechanisms, we investigate the origin of the baryon asymmetry of the Universe. The heavier RHNs generate a lepton asymmetry through out-of-equilibrium decays, including both Standard Model channels and additional flavon-induced processes in which the flavon appears as an intermediate or final-state particle. We compute the corresponding one-loop CP asymmetries and incorporate these effects in the Boltzmann equations. We show that although freeze-in and freeze-out DM production occur in two qualitatively distinct regions of the FN symmetry-breaking scale $v_φ$, successful thermal leptogenesis can be achieved in both regimes. In the large-$v_φ$ (freeze-in-compatible) region the results approach the standard leptogenesis limit, while in the freeze-out-compatible region the lower value of $v_φ$ implies lighter RHNs, requiring resonant enhancement. This tightly constrained framework, in which $v_φ$ simultaneously controls RHN masses and the interaction strengths of the flavon and DM sectors, provides a predictive and unified description of flavor hierarchies, neutrino masses, CP violation, dark matter, and baryogenesis within a single effective theory.

Figures (4)

• Figure 1: Diagrams contributing to the lepton number violating decays of the RHNs, namely, $N_\beta \to H L_\alpha$ and $N_\beta \to \phi L_\alpha$. Besides the presence of the flavon in the final states, their contributions to the loop effects are also shown (in red).
• Figure 2: Evolution of heavy-RHN yields $Y_{N_2}$ (magenta dashed) and $Y_{N_3}$ (purple dashed) as functions of $z=M_\beta/T$ in the freeze-in-compatible scenario. The dotted blue curve shows the equilibrium RHN yield $Y_N^{\rm eq}$, while the solid red curve shows the lepton asymmetry $Y_L$, saturating near $1.6\times10^{-10}$ (black dot-dashed reference line).
• Figure 3: Scan in the $\log v_\phi$--$\log M_{N_2}$ plane for benchmark points yielding $1.5\times10^{-10} \leq Y_L^{\infty} \leq 1.7\times10^{-10}$. Different marker shapes indicate different $\chi^2$ ranges. The color bar, labeled by $|M_{N_3}-M_{N_2}|/M_{N_2}$, shows the required RHN mass degeneracy.
• Figure 4: Evolution of RHN yields $N_2$ and $N_3$ as functions of $z=M_\beta/T$ in the freeze-out-compatible scenario. The color convention is the same as in Fig. \ref{['fig:yield']}.