Baryogenesis with higher dimension operators

We propose a simple model of baryogenesis comprised of the standard model coupled to a singlet $X$ via higher dimension operators $\mathcal{O}$. In the early universe, $X$ is thermalized by $\mathcal{O}$ mediated scattering processes before it decouples relativistically and evolves into a sizable fraction of the total energy density. Eventually, $X$ decays via $\mathcal{O}$ in an out of equilibrium, baryon number and $CP$ violating process that releases entropy and achieves baryogenesis for a broad range of parameters. The decay can also produce a primordial abundance of dark matter. Because $X$ may be as light as a TeV, viable regions of parameter space lie within reach of experimental probes of $n\mathrm{\text{−}}\overline{n}$ oscillation, flavor physics, and proton decay.

Figure 1

The four stages of baryogenesis, shown in terms of the evolution of the energy density in SM radiation and $X$ as a function of scale factor. The decay of $X$ may occur before or after $X$ grows to dominate the total energy density.

Figure 2

Tree and one-loop diagrams for $X_I\to u_i{d}_j{d}_k$ which interfere to produce a primordial baryon asymmetry.

Figure 3

Cosmologically allowed regions of parameter space. The grey region lies outside the regime of the effective theory. The blue region is disfavored by BBN, while the purple region is excluded by the requirements that $X_I$ decouple relativistically and washout be evaded. The yellow region accommodates the observed primordial baryon asymmetry, while the green dashed lines denote the required DM mass in keV.