The homogeneous precession domain (HPD) of superfluid <math><mrow><mmultiscripts><mrow><mi>He</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>3</mn></mrow></mmultiscripts></mrow></math> has recently been identified as a detection medium which might provide sensitivity to the axion-nucleon coupling <math><msub><mi>g</mi><mrow><mi>a</mi><mi>N</mi><mi>N</mi></mrow></msub></math> competitive with, or surpassing, existing experimental proposals. In this work, we make a detailed study of the statistical and dynamical properties of the HPD system in order to make realistic projections for a full-fledged experimental program. We include the effects of clock error and measurement error in a concrete readout scheme using superconducting qubits and quantum metrology. This work also provides a more general framework to describe the statistics associated with the axion gradient coupling through the treatment of a transient resonance with a nonstationary background in a time-series analysis. Incorporating an optimal data-taking and analysis strategy, we project a sensitivity approaching <math><msub><mi>g</mi><mrow><mi>a</mi><mi>N</mi><mi>N</mi></mrow></msub><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>12</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>GeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> across a decade in axion mass.

United States

Joshua W. Foster

China

Christina Gao

William Halperin

Yonatan Kahn

Aarav Mande

Man Nguyen

Japan

Jan Schütte-Engel

John William Scott

Statistics and sensitivity of axion wind detection with the homogeneous precession domain of superfluid helium-3

Axions and axionlike particles may couple to nuclear spins like a weak oscillating effective magnetic field, the “axion wind.” Existing proposals for detecting the axion wind sourced by dark matter exploit analogies to nuclear magnetic resonance (NMR) and aim to detect the small transverse field generated when the axion wind resonantly tips the precessing spins in a polarized sample of material. We describe a new proposal using the homogeneous precession domain of superfluid <math><mrow><mmultiscripts><mrow><mi>He</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>3</mn></mrow></mmultiscripts></mrow></math> as the detection medium, where the effect of the axion wind is a small shift in the precession frequency of a large-amplitude NMR signal. We argue that this setup can provide broadband detection of multiple axion masses simultaneously and has competitive sensitivity to other axion wind experiments such as CASPEr-Wind at masses below <math><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math> by exploiting precision frequency metrology in the readout stage.

Axion Wind Detection with the Homogeneous Precession Domain of Superfluid Helium-3

The surprisingly large value of r , the ratio of power in tensor to scalar density perturbations in the CMB reported by the BICEP2 Collaboration, if confirmed, provides strong evidence for Inflation at the GUT scale. While the Inflationary signal remains the best motivated source, a large value of r alone would still allow for the possibility that a comparable gravitational wave background might result from a self ordering scalar field (SOSF) transition that takes place later at somewhat lower energy. We find that even without detailed considerations of the predicted BICEP signature of such a transition, simple existing limits on the isocurvature contribution to CMB anisotropies would definitively rule out a contribution of more than 5% to râ0.2 . We also present a general relation for the allowed fractional SOSF contribution to r as a function of the ultimate measured value of r . These results point strongly not only to an inflationary origin of the BICEP2 signal, if confirmed, but also to the fact that if the GUT scale is of order 1016Â GeV then either the GUT transition happens before Inflation or the Inflationary transition and the GUT transition must be one and the same.