Evaporating the Milky Way halo and its satellites with inelastic self-interacting dark matter

Self-interacting dark matter provides a promising alternative for the cold dark matter paradigm to solve potential small-scale galaxy formation problems. Nearly all self-interacting dark matter simulations so far have considered only elastic collisions. Here we present simulations of a galactic halo within a generic inelastic model using a novel numerical implementation in the AREPO code to study arbitrary multistate inelastic dark matter scenarios. For this model we find that inelastic self-interactions can: (i) create larger subhalo density cores compared to elastic models for the same cross-section normalization; (ii) lower the abundance of satellites without the need for a power spectrum cut-off; (iii) reduce the total halo mass by about 10{{ per cent}}; (iv) inject the energy equivalent of O(100) million Type II supernovae in galactic haloes through level de-excitation; (v) avoid the gravothermal catastrophe due to removal of particles from halo centres. We conclude that a ∼5 times larger elastic cross-section is required to achieve the same central density reduction as the inelastic model. This implies that well-established constraints on self-interacting cross-sections have to be revised if inelastic collisions are the dominant mode. In this case significantly smaller cross-sections can achieve the same core density reduction thereby increasing the parameter space of allowed models considerably.