LISA could detect low-mass dark matter halos via gravitational lensing
A new study proposes that the future space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) could detect low-mass dark matter halos, with masses between 10 and 10,000 solar masses (M☉). These halos, predicted by cold dark matter models, are sensitive to the fundamental nature of dark matter and the primordial power spectrum, but have remained undetected until now. The proposal is based on the wave-optics lensing effect that multiple dark matter halos would produce on gravitational waves.
The method focuses on the statistical properties of stochastic diffraction, a phenomenon that would imprint correlated fluctuations on the amplitude and phase of the original gravitational waveforms. These stochastic distortions can be described by an orthogonal basis that captures the dominant "tones" associated with dark matter properties, a concept termed "dark timbre." This timbre is not degenerate with binary gravitational wave source parameters, allowing for their distinction.
LISA would be particularly sensitive to dark matter halos in this mass range. Although the per-event signal would be very weak, on the order of 10⁻³ in the cold dark matter model, the study suggests that stacking the signals from 50 to 500 loud binaries (gravitational wave sources) could confirm the existence of these halos with a statistical significance of 2 to 5 standard deviations (σ). This would require major advances in waveform accuracy and data analysis techniques. Even without reaching this direct detection threshold, stochastic diffraction would allow for stringent bounds on models that enhance small-scale structure, such as axion miniclusters or primordial black holes.