Broadband and Resonant Approaches to Axion Dark Matter Detection (1602.01086v3)

Abstract: When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axion-like dark matter with masses in the range of 10^{-14}-10^{-6} eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.

• The paper introduces a novel experimental design that uses both broadband and resonant circuits to significantly extend the sensitivity for axion dark matter detection.
• The methodology leverages superconducting toroidal magnets and pickup loops to measure axion-induced magnetic flux variations within a mass range of 10⁻¹⁴ to 10⁻⁶ eV.
• Quantitative estimates indicate the approach can reach sensitivity down to gₐγγ ≈ 6.3×10⁻¹⁸ GeV⁻¹, surpassing existing experimental limits.

Overview of "Broadband and Resonant Approaches to Axion Dark Matter Detection"

The paper, "Broadband and Resonant Approaches to Axion Dark Matter Detection," authored by Yonatan Kahn, Benjamin R. Safdi, and Jesse Thaler, presents a novel experimental design aimed at detecting axion-like particles (ALPs) that are hypothesized to be components of dark matter. The proposed method employs both broadband and resonant circuits to detect axion effective currents generated in the presence of a static magnetic field, expanding the potential range of detectable axion masses significantly beyond what current technology allows.

Experimental Design and Theoretical Foundation

The authors suggest leveraging a superconducting toroidal magnet to generate a static magnetic field, $B_0$, which, in conjunction with the presence of axion dark matter, induces an oscillating magnetic flux that can be measured through external pickup loops. Importantly, this setup aims to detect axions with masses ranging from $10^{-14}$ to $10^{-6}$ eV, particularly offering sensitivity towards QCD axions with a grand unified theory (GUT) scale decay constant.

The design capitalizes on two signal pickup methods:

1. Broadband Readout Circuit: This method utilizes a superconducting quantum interference device (SQUID) to detect changes in magnetic flux without tuning the magnetometer to resonance. Its broad frequency coverage inherently suits the detection of light axions, taking advantage of longer coherence times at lower masses.
2. Resonant Readout Circuit: Similar to traditional resonant detection methods, this approach aims to enhance the signal at specific resonant frequencies using an $LC$ circuit. Although limited by intrinsic resistance and finite bandwidth, it offers high sensitivity at higher frequencies where $Q$ factors can be optimized.

Numerical Estimates and Prospects for Detection

The experiment's projected sensitivity is quantified over a significant mass range, highlighting the potential to probe QCD axions up to the GUT scale significantly. For instance, with a 1-year data collection span and a magnetic field strength of 5 T, the broadband strategy could achieve detection sensitivity for $g_{a\gamma\gamma}$ as low as $6.3 \times 10^{-18} \ \text{GeV}^{-1}$, contingent upon the axion mass. As depicted in their sensitivity reach figures, such capabilities surpass existing experiments by targeting axion parameters previously considered inaccessible.

Implications and Future Directions

This work underscores a significant enhancement in the experimental landscape for axion detection by proposing methodologies with the capacity to interrogate vast yet unexplored segments of the axion parameter space. Notably, the combination of broadband and resonant circuits allows for complementary exploration, with the former being more suited for lower axion masses and the latter for higher frequencies. Such dual-strategy detection methods may substantially broaden our understanding and acknowledge the potential existence of axion dark matter within the predicted mass range.

Moreover, the authors briefly gesture towards broader applications, such as the detection of dark photon dark matter, thereby hinting at a versatile platform adaptable for various ultralight dark matter candidates.

Concluding Remarks

While the concept of ALPs remains conjectural, the proposed experimental frameworks in the paper offer robust pathways to verify their presence, demonstrating meticulous theoretical grounding and addressing pertinent technological challenges. This serves as a substantial step forward in both theoretical physics and experimental astrophysics, significantly contributing to resolving the open question of dark matter constituents. Future developments in experimental setups and noise reduction techniques will be crucial in realizing these proposed capabilities, potentially leading to discoveries that substantiate the fundamental theories of particle physics.