New observables for direct detection of axion dark matter

Peter W. Graham and Surjeet Rajendran

Phys. Rev. D 88, 035023 – Published 26 August 2013

Abstract

We propose new signals for the direct detection of ultralight dark matter such as the axion. Axion or axionlike particle dark matter may be thought of as a background, classical field. We consider couplings for this field which give rise to observable effects including a nuclear electric dipole moment, and axial nucleon and electron moments. These moments oscillate rapidly with frequencies accessible in the laboratory, $\sim$ kilohertz to gigahertz, given by the dark matter mass. Thus, in contrast to WIMP detection, instead of searching for the hard scattering of a single dark matter particle, we are searching for the coherent effects of the entire classical dark matter field. We calculate current bounds on such time-varying moments and consider a technique utilizing NMR methods to search for the induced spin precession. The parameter space probed by these techniques is well beyond current astrophysical limits and significantly extends laboratory probes. Spin precession is one way to search for these ultralight particles, but there may well be many new types of experiments that can search for dark matter using such time-varying moments.

Received 8 July 2013

DOI:https://doi.org/10.1103/PhysRevD.88.035023

Authors & Affiliations

Peter W. Graham and Surjeet Rajendran

Department of Physics, Stanford Institute for Theoretical Physics, Stanford University, Stanford, California 94305, USA

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Vol. 88, Iss. 3 — 1 August 2013

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Images

Figure 1
Reproduced with permission from Fig. 2 of Ringwald [72], this figure is adapted from 51, 52, 73 (see also 50). ALP parameter space in axion-photon coupling [as in Eq. (3)] versus mass of ALP. The QCD axion is the yellow band. The width of the yellow band gives an indication of the model dependence in this coupling, though the coupling can even be tuned to zero.Reuse & Permissions
Figure 2
ALP parameter space in EDM coupling Eq. (4) versus mass of ALP. The upper (green) region is excluded by excess cooling in SN1987A. The upper left (blue) regions is excluded by the best static nucleon EDM experiments. The diagonal (purple) band is the QCD axion region, with the darker (purple) part showing the most theoretically-motivated region for QCD axion dark matter. The width of the band shows the uncertainty in the calculation of the axion-induced EDM and the axion mass. The ADMX region shows the part of QCD axion parameter space which has been covered (darker, blue) [28] or will be covered in the near future (lighter, blue) [55, 56] by ADMX. For the static EDM and ADMX bounds we assume that the ALP makes up all of the dark matter. See also Fig. 2 of 43 for sensitivity of the proposed NMR experiment.Reuse & Permissions
Figure 3
Geometry of the experiment, adapted from 43. The applied magnetic field ${\vec{B}}_{ext}$ is collinear with the sample magnetization $\vec{M}$ . The relative velocity $\vec{v}$ between the sample and the dark matter ALP field is in any direction that is not collinear with $\vec{M}$ . The SQUID pickup loop is arranged to measure the transverse magnetization of the sample.Reuse & Permissions
Figure 4
ALP parameter space in pseudoscalar coupling of axion to nucleons Eq. (12) versus mass of ALP. The diagonal (purple) band is the region in which the QCD axion may lie. The width of this (purple) band gives an approximation to the axion model-dependence in this coupling. The darker (purple) portion of the line shows the region in which the QCD axion could be all of the dark matter and have $f_{a} < M_{pl}$ as in Fig. 2. The upper (green) region is excluded by SN1987A from 46. The top (blue) region is excluded by searches for new spin-dependent forces between nuclei [64]. The upper solid (red) line is the preliminary sensitivity of an NMR style experiment using Xe; the lower solid (blue) line is the sensitivity using ${}^{3}{He}$ . The dashed lines show the limit from magnetization noise for each sample. These lines assume the parameters in Table . The ADMX region shows the part of QCD axion parameter space which has been covered (darker, blue) [28] or will be covered in the near future (lighter, blue) [55, 56] by ADMX.Reuse & Permissions
Figure 5
ALP parameter space in pseudoscalar coupling of axion to electrons Eq. (18) versus mass of ALP. The upper (green) region is excluded by white dwarf cooling rates from 46. The top (blue) region is excluded by searches for new spin-dependent forces between electrons [70, 71]. The region below the solid diagonal (purple) line shows the possible parameter space for a QCD axion, with the region bounded by darker (purple) solid and dashed lines being the region where the QCD axion could be all of dark matter and have $f_{a} < M_{pl}$ . The frequency range of the QCD axion covered by ADMX is identical to the range plotted in Fig. 4.Reuse & Permissions

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