Oscillation Baryogenesis via Ultraviolet Dark Matter Freeze-In

TL;DR

This paper analyzes baryogenesis from dark matter oscillations in the ultraviolet (UV) freeze-in regime, showing that a joint explanation of the baryon asymmetry and DM abundance is possible for DM masses in the keV–MeV range when the reheat temperature lies between the electroweak scale and roughly 10 TeV. Using an EFT framework that integrates out heavy mediators, the authors solve quantum kinetic equations for DM density matrices to track oscillations, CP violation, and SM lepton asymmetries, identifying viable regions of parameter space with a nearly massless DM eigenstate and a reheat temperature near the TeV scale. They explore both semileptonic and fully leptonic operators, assess perturbative and momentum-averaged approaches, and examine observational constraints from structure formation and X-ray searches that significantly shape the allowed parameter space. The results highlight a delicate balance between producing enough asymmetry and avoiding DM overproduction, with the DM spectrum and reheating history playing crucial roles; certain EFT structures can evade X-ray bounds, while others are tightly constrained, suggesting concrete experimental avenues for testing UV freeze-in baryogenesis in the near future.

Abstract

We investigate baryogenesis from dark matter oscillations in the ultraviolet freeze-in regime. We find that the mechanism can simultaneously accommodate the observed abundances of baryons and dark matter for dark matter masses in the 10 keV to MeV range, provided the reheat temperature lies between the temperature of the electroweak phase transition and ~10 TeV. The mechanism predicts observable consequences due to the presence of a light dark matter component that is relativistic during structure formation, and X-ray bounds on decaying dark matter can set strong constraints depending on the operator mediating dark matter production.

Figures (8)

• Figure 1: Comoving momentum spectrum of DM particles produced from (red) on-shell decay of $\Phi_a$; (blue) $2\to2$ scattering in the EFT with $\Phi_a$ integrated out; (dashed) Fermi-Dirac distribution.
• Figure 2: DM abundances, electron flavor asymmetry $X_e\equiv B/3-\Delta L_e$, and baryon asymmetry $Y_B$ as a function of dimensionless time, $z\equiv T_{\rm ew}/T$, for a benchmark point that simultaneously gives the correct DM energy density and baryon asymmetry: $z_{\rm RH}=0.1$, $M_1=0$, $M_2=100$ keV, $\theta=0.092$, $\mathrm{Tr}D^\dagger D=8.08\times10^{-28}\,\,\mathrm{GeV}^{-4}$. The muon flavor asymmetry, $|X_\mu|$, is not shown because it is nearly indistinguishable from $|X_e|$.
• Figure 3: Coupling consistent with observed baryon asymmetry (shaded blue region) and DM abundance (dashed line) from freeze-in baryogenesis with $z_{\rm RH} \equiv T_{\rm ew}/T_{\rm RH} = 0.1$ and (top left) $M_2=25$ keV; (top right) $M_2=100$ keV; (bottom left) $M_2=400$ keV; (bottom right) $M_2=1600$ keV. We take $M_1=0$ and use the optimized semileptonic coupling benchmark from Appendix \ref{['app:coupling_benchmark']}; we consider a parameter point to successfully achieve the baryon asymmetry if $Y_B\ge Y_B^{\rm obs}$, since it is always possible to make the asymmetry smaller than predicted by the benchmark by modifying $CP$-violating phases in the couplings. For sufficiently large couplings, the asymmetry is suppressed by washout effects, which explains why the shaded blue regions are bounded from above.
• Figure 4: Coupling consistent with observed baryon asymmetry (shaded blue region) and DM abundance (dashed line) from freeze-in baryogenesis with $z_{\rm RH} \equiv T_{\rm ew}/T_{\rm RH} = 0.02$ and (top left) $M_2=100$ keV; (top right) $M_2=500$ keV; (bottom left) $M_2=1000$ keV; (bottom right) $M_2=2000$ keV. We take $M_1=0$ and other parameters the same as in Fig. \ref{['fig:UV_masslesschi1_z0_0p1']}.
• Figure 5: Parameter space for viable baryogenesis, shaded in blue, as a function of $M_1$ and coupling parameter $\theta$ for $z_{\rm RH}=0.1$ and (top left) $M_2=50$ keV; (top right) $M_2=200$ keV; (bottom) $M_2=800$ keV. The other coupling parameters are fixed to obtain the correct total DM abundance while optimizing the asymmetry. The red and yellow shaded regions are excluded from structure formation constraints on a warm fraction of the total DM abundance ($\Omega_{\chi_1}/\Omega_{\rm DM}<0.1$) Boyarsky_2009Kamada:2016vscBaur_2017, and constraints on a light but massive relic (LiMR) from CMB, BOSS, and weak lensing Xu:2021rwg, respectively; see Sec. \ref{['sec:structure']} for more details. Note that $M_1\lesssim 0.1$ keV for all parameters consistent with constraints giving successful leptogenesis.