Ultralight dark matter and fifth forces with atomic sensors

6 problems

• Exotic spin-dependent forces between electrons and nucleons

  Open

  New particles could make spinning electrons or nuclei attract or repel each other in ways depending on spin direction and velocity. Magnetometers, comagnetometers and diamond defect sensors look for these forces at distances from micrometers to meters.

• Nuclear-structure origin of King-plot nonlinearity in Yb and Ca

  Partially resolved

  Comparing the frequency shifts between isotopes of the same element for two transitions should give a straight line, called a King plot, unless a new force between electrons and neutrons bends it. In ytterbium and calcium the line is bent, and the cause appears to be nuclear structure, but that has to be predicted quantitatively before the method can find new forces.

• Axion-mediated monopole-dipole nucleon force at submillimeter range

  Open

  An axion could make an ordinary lump of matter push slightly on nearby nuclear spins, as if the spins felt a weak magnetic field that ordinary magnetic shielding cannot block. Nuclear magnetic resonance next to a rotating source mass looks for this push at distances below a millimeter.

• Axion-induced oscillating nucleon EDM at QCD-axion strength

  Open

  An axion, a proposed very light particle, would give neutrons and protons a tiny electric dipole that oscillates in time. Nuclear magnetic resonance experiments look for the resulting wobble of nuclear spins.

• Scalar ultralight dark matter coupled to photons: detect or exclude

  Open

  A scalar dark matter field (a field with no direction, like temperature) oscillating at its mass frequency would make $\alpha$ oscillate. Networks of clocks can look for this oscillation over a huge range of masses.

• Correct treatment of the stochastic dark-matter field amplitude in limits

  Partially resolved

  A wave-like dark matter field is a sum of many waves with random phases, so its local strength fluctuates. Searches shorter than the field coherence time can be unlucky, and limits must account for this.