The universe could be symmetric: dark matter stability and matter-antimatter asymmetry from baryon number conservation

There is great evidence that dark matter constitutes most of the matter content in our universe. We also have measured a cosmological asymmetry between matter and antimatter. The nature of dark matter remains elusive, as does the origin of the matter-antimatter asymmetry. Still, the similarity between their current abundances hints towards a common origin. Also, as we can only see the visible component of matter, we cannot state that the universe is overall asymmetric. In this work, we study the possibility that the dark matter carries baryon number and hides the counterpart of the measured asymmetry. We introduce a model with two dark sector particles, one scalar and one fermion, carrying baryon number and initially having equal but opposite asymmetries. Following the principle of baryon number conservation, the particles in the dark sector interact with each other, and the fermionic one interacts with the Standard Model through the Neutron Portal. The scalar particle freezes out and generates the dark matter relic density, as it is naturally stable. The fermionic particle or "dark neutron" disappears from the thermal bath and transfers its asymmetry to the quarks via scatterings and decays. This scenario is viable and consistent with cosmological observations and collider constraints. Different phenomenological considerations entirely bound the parameter space available for the Neutron Portal and could be probed in the future.