New Observables for Direct Detection of Axion Dark Matter (1306.6088v2)

Abstract: We propose new signals for the direct detection of ultralight dark matter such as the axion. Axion or axion like particle (ALP) 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, ~ kHz to GHz, 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.

• The paper introduces oscillating nucleon EDMs and axial moments as novel observables for axion dark matter detection.
• It employs nuclear magnetic resonance techniques to amplify axion-induced signals, exploring previously inaccessible parameter spaces.
• The proposed methods offer practical experimental pathways to detect high decay constant axions, potentially reaching the QCD axion regime.

Overview of "New Observables for Direct Detection of Axion Dark Matter"

The paper "New Observables for Direct Detection of Axion Dark Matter" by Peter W. Graham and Surjeet Rajendran proposes innovative methodologies for the detection of ultralight dark matter candidates, specifically focusing on axion and axion-like particles (ALPs). Unlike conventional approaches that often target weakly interacting massive particles (WIMPs), this research shifts towards leveraging the coherent, classical field nature of axion dark matter to explore novel detection paradigms.

Key Concepts and Methodologies

The authors propose that axion dark matter, acting as a classical field, could lead to detectable interactions with Standard Model particles that manifest as oscillating signals. This contrasts sharply with the traditional WIMP detection techniques aiming to register distinct scattering events. The main observables discussed include nucleon electric dipole moments (EDMs) and axial moments of nucleons and electrons, which oscillate with frequencies substantially lower than those of previous considerations.

1. Nucleon Electric Dipole Moments (EDMs):
   • The paper outlines how the interaction between the axion field and nuclear particles might induce time-varying EDMs. Unlike static EDM searches, this signal oscillates at the same frequency as the axion's mass—ranging from kHz to GHz. The strength of this oscillation does not diminish with increasing axion decay constant $f_a$, presenting a robust observable beyond previous static EDM experiments.
2. Axial Nucleon and Electron Moments:
   • Similar to the EDM, axions may induce oscillating axial moments resulting in a discernible spin precession of nucleons and electrons. This effect can be harnessed through nuclear magnetic resonance (NMR) techniques to detect a time-varying signal in precision magnetometry. This mechanism allows for substantial signal amplification through resonance.

Potential of the Proposed Techniques

The techniques proposed in the paper probe significantly unexplored parameter spaces for dark matter detection, extending well beyond existing astrophysical and laboratory constraints. The authors emphasize the potential of NMR methods and sensitive magnetometry for accessing vast regions of the axion parameter space that are either inaccessible or inadequately explored by current methods. This approach holds particularly strong prospects for detecting the QCD axion with decay constants approaching the Planck scale.

Implications and Future Directions

The implications of the research are substantial, pivoting from conventional energy deposition approaches to exploiting coherent field properties, fundamentally shifting detection methodologies. Theoretically, these techniques suggest further avenues of inquiry into high energy scales and provide a method to explore the quintessential properties of scalar fields as potential dark matter candidates. Practically, they open new experimental pathways involving sensitive spin precession measurements, with implications extending to the next generation of dark matter direct detection experiments. The paper suggests that this paradigm shift could place even high decay constant axions within experimental reach, a region previously thought inaccessible.

Conclusion

In summary, this paper introduces a compelling framework for axion dark matter research, providing an innovative shift in detection strategies. By focusing on continuous field effects rather than individual particle interactions, the authors have charted a path that could substantially alter our approach to understanding and detecting dark matter. The methodologies outlined have the potential to stimulate further experimental and theoretical work, particularly in developing technologies capable of exploiting these unique axion couplings.