Probing mixed-state dark matter and $b \to s \mu^+\mu^-$ anomalies in a scalar-assisted baryonic gauge theory

Abstract

We explore a Standard Model extension based on a local $U(1)_B$ symmetry, where a baryon-charged scalar mediates interactions between a fermionic dark matter candidate and Standard Model quarks. In this setup, the dark matter relic abundance is shaped not only by standard annihilation channels but also by additional coannihilation processes induced by a new scalar. The presence of this mediator provides a unified link between dark sector and flavor physics, yielding distinctive phenomenological consequences. We conduct a detailed study of dark matter phenomenology, emphasizing the role of the mass splitting between the dark matter particles, and the scalar mediator in determining the efficiency of coannihilation. The parameter space is examined in light of existing constraints from cosmological observations, direct and indirect detection experiments, as well as the collider searches at the \texttt{LHC}. Our analysis shows that the extended scalar sector opens up viable regions of parameter space beyond those accessible in minimal \(U(1)_B\) realizations, many of which are expected to be tested by forthcoming searches at \texttt{XENONnT} and \texttt{CTA}. Moreover, the model induces correlated signatures from flavor observables associated with the $b \to s \mu^+ \mu^-$ transitions as well, serving as complementary tests of the underlying framework.