Are Subleading Effects Really Subleading? $B$-Meson Decays in Mesogenesis

We calculate inclusive $B$-meson decay rates in the Mesogenesis framework, a model explaining baryogenesis and the existence of dark matter, using the Heavy Quark Expansion (HQE), up to the dimension-six two-quark Darwin term. By systematically studying the power-suppressed contributions, we identify regions of parameter space where subleading terms exceed the leading contribution, i.e., the free $b$-quark decay, highlighting the limits of the HQE in this BSM scenario. This behavior is reminiscent of the Standard Model only under artificially heavy charm masses, and can be used to study the HQE close to its breakdown. We further update the lower bounds on the exclusive decay mode $B^+ \to p^+ ψ$ by incorporating the fully HQE-corrected inclusive width in the ratio $Γ_{\mathrm{excl}}/Γ_{\mathrm{incl}}$. Extending the analysis from total decay rates to the lifetime ratio $τ(B_s)/τ(B_d)$, we find no additional constraints on the couplings beyond existing collider bounds, consistent with analogous results for $τ(B^+)/τ(B_d)$. We further compare the sensitivity of both lifetime ratios.