$\text{Dark}_{CP}$ Mesogenesis and New Implications for Collider Searches

TL;DR

This work addresses the origin of the baryon asymmetry by proposing Dark_CP Mesogenesis, a minimal variant in which CP violation is entirely in the dark sector and SM mesons decay out of equilibrium into SM baryons and dark-sector baryons. The mechanism operates during a late-time, low-temperature reheating era and relies on a four-fermion interaction mediated by a heavy colored scalar, yielding BAU even for tiny exotic branching fractions and establishing a lower bound Br($\mathcal{M}\to \mathcal{B}_{SM}+\text{MET}$) $\gtrsim 10^{-8}$ when $A_{CP}^{\rm dark}$ is order one. The paper derives Boltzmann-evolution results, maps the viable parameter space, and outlines tangible collider signatures: direct decays at $B$-factories, indirect LHCb probes, and a dark-lepton leptogenesis variant. It also presents a concrete dark-sector content, discusses EDM constraints, and provides a comprehensive roadmap for testing or excluding the Mesogenesis framework across current and future experiments, including potential caveats from late-time dark phase transitions. Together, these results offer a clear, testable path to either discover or decisively constrain Mesogenesis as a mechanism for the BAU and dark matter production.

Abstract

We introduce $\text{Dark}_{CP}$ Mesogenesis in which Standard Model mesons, either $B_{s,d}^0$, $B^\pm$ or $B_c^\pm$, undergo out-of-equilibrium dark CP violating decays to Standard Model and dark sector baryons. With order one CP violation in the dark sector, the observed baryon asymmetry of the Universe can then be generated with branching fractions as small as $2.7 \times 10^{-8}$ for the exotic decay of $B$-mesons into baryons and missing energy. This sets a lower limit on the branching fraction below which Mesogenesis becomes disfavored. This work therefore strongly encourages collider searches to target sensitivities one to three orders of magnitude below planned limits. For completeness, we further introduce a variant on $\text{Dark}_{CP}$ Mesogenesis involving dark lepton states. We conclude by laying out a roadmap for the complete exclusion (or discovery) of the Mesogenesis framework.

Figures (6)

• Figure 1: A depiction of the $\text{Dark}_{\rm CP}$ Mesogenesis mechanism where the mesons $\mathcal{M}$ undergo kinematically allowed decays to Standard Model and dark baryons. CP violation arises in the $\mathcal{M}$ meson decay itself through 1-loop and tree level interference from diagrams with additional dark sector fermion flavors.
• Figure 2: Benchmark points corresponding to solving the Boltzmann equations for the baryon asymmetry Eq. \ref{['eq:asymBE']} in conjunction with Eq. \ref{['eq:PhiRadBE']}. $\text{Br}_\Phi^{\mathcal{M}}$ is assumed to be one for a given $\mathcal{M}$ under consideration. Note that the small differences between dashed and dotted line implies results will be relatively insensitive to $T_R$.
• Figure 3: Parameter space for successful $\text{Dark}_{\rm CP}$ Mesogenesis is shown in blue. Light blue corresponds to the washout regime where the baryon asymmetry is initially overproduced. Dotted lines correspond to existing neutral $B$ Mesogenesis searches BaBar:2023rerBelle:2021gmcBaBar:2023dtqBaBar:2024qqx, while the branching fractions greater than $10^{-2}$ are excluded by ALEPH Alonso-Alvarez:2021qfd.
• Figure 4: Diagrams whose interferes leads to CP violation in meson decays when of-shell $\psi_{\mathcal{B}}$s decay to $\phi_{\mathcal{B}} \, \xi$.
• Figure 5: A Feynman diagram involving the dark sector states contributing to the CP-violating three gluon operator the Standard Model. A similar diagram where two gluons attach to the $\mathcal{Y}$ line and one to the quark line is not shown.