The mass of the dark matter particle is unknown, and may be as low as ∼10 −22 eV. The lighter part of this range, below ∼ eV, is relatively unexplored both theoretically and experimentally but contains an array of natural dark matter candidates. An example is the relaxion, a light boson predicted by cosmological solutions to the hierarchy problem. One of the few generic signals such light dark matter can produce is a time-oscillating, EP-violating force. We propose searches for this using accelerometers, and consider in detail the examples of torsion balances, atom interferometry, and pulsar timing. These approaches have the potential to probe large parts of unexplored parameter space in the next several years. Thus such accelerometers provide radically new avenues for the direct detection of dark matter.

We used a torsion pendulum and rotating attractor with 20-pole electron-spin distributions to probe dipole-dipole interactions mediated by exotic pseudo-Goldstone bosons with m b ≤ 500 µeV and coupling strengths up to 14 orders of magnitude weaker than electromagnetism. This corresponds to symmetry-breaking scales F ≤ 70 TeV, the highest reached in any laboratory experiment. We used an attractor with a 20-pole unpolarized mass distribution to improve laboratory bounds on CP -violating monopole-dipole interactions with 1.5 µeV< m b < 400 µeV by a factor of up to 1000.

Axionlike particles are promising candidates to make up the dark matter of the Universe, but it is challenging to design experiments that can detect them over their entire allowed mass range. Dark matter in general, and, in particular, axionlike particles and hidden photons, can be as light as roughly 10 −22 eV (∼10 −8 Hz), with astrophysical anomalies providing motivation for the lightest masses ("fuzzy dark matter"). We propose experimental techniques for direct detection of axionlike dark matter in the mass range from roughly 10 −13 eV (∼10 2 Hz) down to the lowest possible masses. In this range, these axionlike particles act as a time-oscillating magnetic field coupling only to spin, inducing effects such as a timeoscillating torque and periodic variations in the spin-precession frequency with the frequency and direction of these effects set by the axion field. We describe how these signals can be measured using existing experimental technology, including torsion pendulums, atomic magnetometers, and atom interferometry. These experiments demonstrate a strong discovery capability, with future iterations of these experiments capable of pushing several orders of magnitude past current astrophysical bounds.

We surrounded a rotating torsion pendulum containing 9.8×10(22) polarized electrons by 2 or 4 stationary sources, each with a net spin of 6.0×10(24) polarized electrons. Multiple source configurations gave sensitivity to hypothetical dipole-dipole, spin-dot-spin, and spin-cross-spin exchange interactions mediated by bosons with masses up to 20 μeV. For bosons with masses ≤0.1 μeV our null results for the dipole-dipole, spin-dot-spin, and spin-cross-spin forces imply 1σ upper limits on (g(P)(e))(2)/(ħc), (g(A)(e))(2)/(ħc) and (g(V)(e)g(A)(e))/(ħc) of 2.2×10(-16), 3.8×10(-40), and 1.2×10(-28), respectively. We also constrain, for the first time, any possible linear combination of static spin-spin interactions. In this case our upper limits relax to 5.6×10(-16), 9.8×10(-40), and 1.2×10(-28), respectively.

We report results of a new technique to measure the electric dipole moment of 129 Xe with 3 He comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is dA( 129 Xe) = (1.4 ± 6.6stat ± 2.0syst) × 10 −28 e cm. This corresponds to an upper limit of |dA( 129 Xe)| < 1.4 × 10 −27 e cm (95% CL), a factor of five more sensitive than the limit set in 2001.Searches for permanent electric dipole moments (EDMs) are a powerful way to investigate beyondstandard-model (BSM) physics. An EDM is a charge asymmetry along the total angular momentum axis of a particle or system and is odd under both parity reversal (P) and time reversal (T). Assuming CPT conservation (C is charge conjugation), an EDM is a direct signal of CP violation (CPV), a condition required to generate the observed baryon asymmetry of the universe [1]. The Standard Model incorporates CPV through the phase in the CKM matrix and the QCD parameterθ. However, the Standard Model alone is insufficient to explain the size of the baryon asymmetry [2]. BSM scenarios that generate the observed baryon asymmetry [3] generally also provide for EDMs larger than the SM estimate, which for 129 Xe is |d A ( 129 Xe) SM | ≈ 5 × 10 −35 e cm [4].EDM measurements have provided constraints on how BSM CPV can enter low-energy physics [4]. Diamagnetic systems such as 129 Xe and 199 Hg are particularly sensitive to CPV nucleon-nucleon interactions that induce a nuclear Schiff moment and CPV semileptonic couplings [7]. While the most precise atomic EDM measurement is from 199 Hg [8], there are theoretical challenges to constraining hadronic CPV parameters from 199 Hg alone, and improved sensitivity to the 129 Xe EDM would tighten these constraints [7,9]. Additionally, recent work has shown that contributions from light-axion-induced CPV are significantly stronger for 129 Xe than for 199

We analyzed an 6.7-year span of data from a rotating torsion-pendulum containing ≈ 10 23 polarized electrons to search for the "wind" arising from ultralight, axionlike dark matter with masses between 10 −23 and 10 −18 eV/c 2 . Over much of this range we set a 95% confidence limit Fa/Ce > 2 × 10 15 eV on the axionlike decay constant. PACS numbers: 95.35+d,98.35Gi,14.80.Va

Polarized nuclei are a powerful tool in nuclear spin studies and in searches for beyond-the-standard model physics. Noble-gas comagnetometer systems, which compare two nuclear species, have thus far been limited by anomalous frequency variations of unknown origin. We studied the self-interactions in a 3 He-129 Xe system by independently addressing, controlling and measuring the influence of each component of the nuclear spin polarization. Our results directly rule out prior explanations of the shifts, and demonstrate experimentally that they can be explained by species dependent self-interactions. We also report the first gas phase frequency shift induced by 129 Xe on 3 He.

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