Improved treatment of bosonic dark matter dynamics in neutron stars: consequences and constraints

It is conceivable that a bosonic dark matter (DM) with non-gravitational interactions with SM particles will be accumulated at the center of a neutron star (NS) and can lead to black hole formation. In contrast to previous works with a fixed NS temperature, we dynamically determine the formation of Bose-Einstein condensate (BEC) for a given set of DM parameters, namely the DM-neutron scattering cross-section (σχn), the thermal average of DM annihilation cross-section (⟨σv⟩) and the DM mass (mχ). For both non-annihilating and annihilating DM with ⟨σv⟩ ≲ 10-26 cm3 s-1, the BEC forms for mχ ≲ 10 TeV. In case of non-annihilating DM, observations of old NS allows σχn ≲ 10-52 cm2 for 10 MeV ≤ mχ ≲ 10 GeV (with BEC) and σχn ≲ 10-47 cm2 for 5 TeV ≲ mχ ≲ 30 PeV (without BEC). This analysis shows that the electroweak mass window, 10 GeV ≲ mχ ≲ 5 TeV is essentially unconstrained by NS observations and therefore is subject only to direct detection experiments. In the annihilating DM scenario, the exclusion limits on DM parameters become weaker and even vanish for typical WIMP annihilation cross-section. However, the late-time heating of the NS enables us to probe the region with σχn ≳ 10-47 cm2, using the James Webb Space Telescope in the foreseeable future. When our results are viewed in the context of indirect searches of DM, it provides a lower limit on the ⟨σv⟩, which is sensitive to the DM thermal state.