Asymmetric Cannibal Dark Matter: Constraints from Neutron Star

Asymmetric dark matter can be efficiently captured by neutron stars via elastic scattering with nucleons and dark matter self scattering. The accumulated dark matter thermalizes and concentrates in the stellar interior, forming a dark matter core. In this work, we propose a novel framework in which a $\mathbb{Z}_3$ symmetry allows for number-changing self-interactions of the form $3 \rightarrow 2$ within the dark sector. These cannibalistic reactions become increasingly efficient at high dark matter densities, leading to a significant depletion of the dark matter population in the stellar core. This number depletion heats up the neutron star above the standard cooling expectations, yielding observable thermal signatures in relatively old, isolated neutron stars, potentially detectable via future infrared telescopes. We show that even in the presence of other heating mechanisms, e.g. dark matter annihilation and kinetic heating, the cannibal heating dominates for certain parameter space. We demonstrate that the cannibal heating can predict detectable heating signatures in old neutron stars, thereby allowing a broader range of viable dark matter masses and couplings to the Standard Model.