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Direct detection of ultralight dark matter bound to the Sun with space quantum sensors


Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks.

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Fig. 1: Maximum SH density.
Fig. 2: Sensitivity estimate for space quantum clocks.
Fig. 3: Maximum SH density as function of distance.
Fig. 4: Maximum SH density at 0.1 au with contours.
Fig. 5: SH coherence time.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The code that generated the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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We thank K. Abazajian, A. Cooray, C. Chen, J. Feng, M. Kaplinghat, H. Kim, D. Leibrandt, G. Perez, S. Profumo and T. Tait for useful discussions. We also thank A. Case and P. Whittlesey for the detailed discussions of instrumentation and environments in space missions, especially the solar probes. We thank D. Budker, Y. Stadnik, P. Thirolf and N. Yu for comments on the manuscript. The work of Y.-D.T. is supported in part by NSF Grant PHY-2210283 and in part by Simons Foundation Grant No. 623683. Part of this document was prepared by Y.-D.T. using the resources of the Fermi National Accelerator Laboratory (Fermilab), a US Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under contract No. DE-AC02-07CH11359. The work of J. E. was supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan, and by the Japanese Society for the Promotion of Science KAKENHI grant Nos. 21H05451 and 21K20366. This work is supported in part by US NSF grants Nos. PHY-2012068 and OMA-2016244. This work is a part of the ‘Thorium Nuclear Clock’ project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 856415). Part of this work was performed at the Aspen Center for Physics, which is supported by the National Science Foundation grant no. PHY-1607611. We also thank the Simons Foundation for its generous support. J. E. thanks the Galileo Galilei Institute for Theoretical Physics for hospitality and the Istituto Nazionale Fisica Nuclear for partial support during the completion of this work.

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All authors contributed to the writing and reviewing of the manuscript. Y.-D.T. conceived the preliminary ideas, initiated the DM study and studied further applications of space quantum clocks (including the spatial variation of fundamental constants and future applications) while cross-checking all results. J.E. analysed the properties of SHs and produced the final figures used in the manuscript. M.S.S. provided expertise on clock technologies and related sensitivity estimates.

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Correspondence to Yu-Dai Tsai, Joshua Eby or Marianna S. Safronova.

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Supplementary discussion sections (RELATED STUDIES IN ULDM, CLOCKS IN EARTH ORBITS AND AN EARTH-BOUND HALO), Supplementary Figure S1.

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Tsai, YD., Eby, J. & Safronova, M.S. Direct detection of ultralight dark matter bound to the Sun with space quantum sensors. Nat Astron 7, 113–121 (2023).

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