From $B_c$ mesons to the baryon asymmetry: a unified $B$ Mesogenesis Framework

Abstract

$B$ mesogenesis offers an interesting mechanism to generate the baryon asymmetry of the universe by converting the CP violation of the Standard Model into a net baryon number asymmetry. In this work we refine and extend the $B$ mesogenesis framework by incorporating all relevant $B$ meson channels active after low-temperature reheating. We first update the known neutral-meson contribution using time-integrated decay rates. While the $B_s^0$ contribution remains essentially unchanged, we find a suppression of the $B_d^0$ term by a factor $\sim 0.4$ with respect to previous analyses, alleviating the tension associated with its expected negative sign. We then perform a systematic study of $B_c^+$ decays, which are basically unexplored. We provide branching-ratio predictions using both leading-order factorization and a data-driven approach inspired by $D\to M_1M_2$ decays. These estimates allow us to quantify two $B_c^+$ sources of mesogenesis: the previously discussed $B_c^+ \to B^+ M^0$ channel and a new mechanism introduced in this work, $B_c^+ \to B_q^0 M$, in which the asymmetry is generated by combining direct CP violation with neutral-meson oscillations. Interestingly, in these channels the charm quark decays. Therefore, these decays give access to {\it charm CP violation} in modes with percent level branching ratios. With moderate assumptions, we find that $B_c^+$ mesogenesis can match or exceed the neutral contribution. Finally, we combine all three mechanisms and explore their viability in terms of the direct CP asymmetry, neutral-meson mixing parameters and early-universe fragmentation fractions. We find that successful baryogenesis can be achieved in a broad parameter space, showing the viability of $B$ mesogenesis. Future measurements of $B_c^+$ modes are thus highly anticipated to further probe the viability of unified $B$ mesogenesis.