Abstract
The next generation of ultralight dark matter (DM) direct detection experiments, which could confirm sub-eV bosons as the dominant source of DM, will feature multiple detectors operating at various terrestrial locations. As a result of the wave-like nature of ultralight DM, spatially separated detectors will each measure a unique DM phase. When the separation between experiments is comparable to the DM coherence length, the spatially-varying phase contains information beyond that which is accessible at a single detector. We introduce a formalism to extract this information, which performs interferometry directly on the DM wave. In particular, we develop a likelihood-based framework that combines data from multiple experiments to constrain directional information about the DM phase space distribution. We show that the signal in multiple detectors is subject to a daily modulation effect unique to wave-like DM. Leveraging daily modulation, we illustrate that within days of an initial discovery multiple detectors acting in unison could localize directional parameters of the DM velocity distribution such as the direction of the solar velocity to sub-degree accuracy, or the direction of a putative cold DM stream to the sub-arcminute level. We outline how to optimize the locations of multiple detectors with either resonant cavity (such as ADMX or HAYSTAC) or quasistatic (such as ABRACADABRA or DM-Radio) readouts to have maximal sensitivity to the full 3-dimensional DM velocity distribution.
Highlights
Cold, bosonic dark matter (DM) candidates with masses much smaller than the eV scale have macroscopic occupation numbers and may be described in the solar vicinity by classical fields
In this work we have demonstrated the power of DM interferometry for wavelike DM
The spatial coherence of the DM field imprints phase correlations on the signals observed at spatially separated detectors, and these phase correlations are sensitive to parameters in the full threedimensional velocity distribution fðvÞ, whereas a single detector is blind to all effects beyond the speed distribution fðvÞ
Summary
Bosonic dark matter (DM) candidates with masses much smaller than the eV scale have macroscopic occupation numbers and may be described in the solar vicinity by classical fields. Due to the nonzero velocity dispersion v0, DM waves are coherent up to distances of order λc; as we will show, phase-sensitive data combined from two experiments exhibit maximal modulation when d ≡ jx12j ∼ λc, or d∼. Reference [44] points out the possibility of observing this daily modulation effect for experiments separated by distances of order λc; here we extend this analysis by focusing on constraining directional parameters in the phase space distribution. The modified speed distributions exhibit daily modulation and carry additional information about the velocity distribution fðvÞ that would be invisible to a single detector For this example we take mDM 1⁄4 25.2 μeV [49], near the window where the HAYSTAC collaboration is searching for axion DM. In Appendix A we provide a brief review of the coherence length and time
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