Future directions in the microwave cavity search for dark matter axions

Abstract

The axion is a light pseudoscalar particle which suppresses CP-violating effects in strong interactions and also happens to be an excellent dark matter candidate. Axions constituting the dark matter halo of our galaxy may be detected by their resonant conversion to photons in a microwave cavity permeated by a magnetic field. The current generation of the microwave cavity experiment has demonstrated sensitivity to plausible axion models, and upgrades in progress should achieve the sensitivity required for a definitive search, at least for low mass axions. However, a comprehensive strategy for scanning the entire mass range, from 1-1000 µeV, will require significant technological advances to maintain the needed sensitivity at higher frequencies. Such advances could include sub-quantum-limited amplifiers based on squeezed vacuum states, bolometers, and/or superconducting microwave cavities. The Axion Dark Matter eXperiment at High Frequencies (ADMX-HF) represents both a pathfinder for first data in the 20-100 µeV range (∼5-25 GHz), and an innovation test-bed for these concepts.

Axion Dark Matter Coupling to Resonant Photons via Magnetic Field

“…This signal is then resonantly enhanced by a cavity structure and resolved above the thermal noise of the measurement system. It has been well established that in a Haloscope with an axial DC magnetic field the expected power due to axion-tophoton conversion is given by [7][8][9] where g γ is a dimensionless model-dependent parameter of O(1) [10][11][12], α the fine structure constant, f a the Peccei-Quinn energy breaking scale which dictates the axion mass and coupling strength, m a the axion mass, ρ a the local density of axions, V the cavity volume, B 0 the applied magnetic field, Q the cavity quality factor (assuming the bandwidth is greater than the expected spread of the axion signal) and C the Haloscope form factor describing the overlap between the electric field created by the converted axions and the electric field structure of the resonant mode in the cavity.To date Haloscope searches have excluded some areas of the parameter space [9,13], with further experiments currently under way and future efforts in various stages of planning [14][15][16]. All of this work fundamentally relies on Eq.…”

Axion Dark Matter Detection Using Atomic Transitions

“…However, because the axion mass is poorly constrained, one wishes to search over as large a range as possible. The range of the cavity experiment is being extended [10] and other detection methods [11][12][13] have been proposed and are being explored but these efforts have not produced limits yet. Here we propose searching for axion dark matter by detecting atomic transitions in which axions are absorbed.…”

Axion detection with negatively coupled cavity arrays

“…2, which demonstrates the factor of N scaling law. The same result can be obtained by power combining N independent cavities, but this introduces many complex technical challenges [8][9][10]. Recent work suggest that post-processing the data acquired from N independent cavities may yield a small improvement over the system proposed here, although, this would require N independent measurement systems [29].…”

“…As the frequency space pushes towards higher frequencies, detector cavity sizes shrink decreasing the mode volume and corresponding sensitivity. An obvious solution to the problem is to increase the number of detecting cavities [8][9][10][11][12]. Unfortunately, this immediately leads to an increase in system complexity as such a system requires the need for additional amplifiers, microwave lines, etc.…”