Transient axion streams from disrupted miniclusters
We investigate the formation and evolution of axion streams generated by the tidal disruption of axion miniclusters through stellar encounters in the Milky Way halo. Combining a large-scale Monte Carlo treatment of repeated stellar flybys with a tracer reconstruction of the stripped debris, we follow the phase-space evolution of the streams across a broad range of galactocentric radii and assess their contribution to the local dark matter distribution. We find that the kinetic energy of the stripped debris typically exceeds its residual self-gravitational binding energy at formation, so that the subsequent evolution is dominated by anisotropic free expansion and orbital shear. As a result, stream densities can decrease by factors as large as $\sim10^{-9}$ over Galactic timescales, strongly suppressing the steady-state abundance of dense streams near the Solar circle. At the Solar radius, only a small fraction of realizations yields a nonzero encounter probability over a 10-year exposure, implying that observable streams are dominated by rare recent and nearby disruption events rather than by a persistent population of long-lived overdense substructure. Despite this rapid dilution, the streams remain dynamically cold and produce detector-frame linewidths many orders of magnitude narrower than the cavity bandwidths of current haloscope experiments. For representative haloscope configurations, we find characteristic stream linewidths in the range $Δν_{\rm stream}\sim10^{-7}\mathrm{-}10^{1}\,{\rm Hz}$, while the corresponding Doppler drift remains well below the cavity response width.