New bounds on dark matter coupling from a global network of optical atomic clocks

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Science Advances  07 Dec 2018:
Vol. 4, no. 12, eaau4869
DOI: 10.1126/sciadv.aau4869


  • Fig. 1 Global sensor network.

    The participating optical lattice atomic clocks reside at NIST, Boulder, CO, USA (23, 24), at LNE-SYRTE, Paris, France (25, 26), at KL FAMO, Torun, Poland (27, 28), and at NICT, Tokyo, Japan (29, 30).

  • Fig. 2 Cross correlation of two Embedded Image.

    Left: Overlapping normalized signals, Embedded Image, from the NIST and LNE-SYRTE laboratories (pink and blue lines, respectively). Right: Cross correlation, A(τ), of the two Embedded Image (brown line) and the fit of the expected cross-correlation function assuming a square perturbation with duration of 30 s (green line). τ is the cross-correlation displacement. The inset depicts the magnification of the region where the fitted triangular function can be seen.

  • Fig. 3 Constraints on the energy scale Λγ,2 and the fine-structure variation δα/α.

    Top right: Constraints (95% CL) on the fine-structure variation δα/α (red line). Top left and bottom: Constraints (95% CLs) on the energy scale Λγ,2 under the assumption of the local mean cold DM energy density ρDM = 0.468 GeV cm−3 (red line) (3, 36). The black and green lines are the direct fit and the 5% CL, respectively. The orange lines represent the previous best constraints measured with two colocated 88Sr clocks (12), and the gray solid and dashed lines represent the actual and possible constraints, respectively, estimated from the Global Positioning System (GPS) constellation’s on-board clocks (15, 16). The topological defect (TD) size, d, can be expressed as the TD field mass scale mTD = ℏ/(dc). The constraints in the top left panel have a discontinuity at T ≈ 3000 s because the ri(t) from the most stable clock in our network (NIST, Boulder, CO, USA) was collected over a shorter duration. The full range of the defect size, d, concerns the domain-wall type of TDs, whose transverse dimensions (regardless the d parameter) are much larger than the span of our network.

  • Fig. 4 Upper limits on the coupling constant de.

    Left: Periodogram of the square of the fitted amplitude A(ω) (light blue). The A2(ω) distribution in the data is consistent with pink (flicker) noise (37). Green and red curves depict the 5 and 95% CLs, respectively. The black curve corresponds to the mean value based on the assumed noise model. The brown curve is the detection threshold. Right: Limit on de derived from our measurement. The blue curve depicts the observed fit. The red curve depicts our limit on de, i.e., the 95% CL. The magenta and orange lines are the 95% confidence limits reported in (13) and (14), respectively. The green line is the result derived from the stability analysis of a single optical atomic clock (15). The brown line represents the equivalence principle tests such as the Eöt-Wash experiment (38) and Lunar Laser Ranging (39). The black line represents the first results of the MICROSCOPE experiment (40).

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