Axion Haloscope Research Articles

Sequential hypothesis testing for axion haloscopes

Sequential hypothesis testing for axion haloscopes

Limits on Dark Photons, Scalars, and Axion‐Electromagnetodynamics with the ORGAN Experiment

AbstractAxions are a well‐motivated dark matter candidate, with a host of experiments around the world searching for direct evidence of their existence. The ORGAN Experiment is a type of axion detector known as an axion haloscope, which takes the form of a cryogenic resonant cavity embedded in a strong magnetic field. ORGAN recently completed Phase 1a, a scan for axions ≈65 µeV, and placed the most stringent limits to date on the dark matter axion–photon coupling in this region, . It has been shown that axion haloscopes such as ORGAN are automatically sensitive to other kinds of dark matter candidates, such as dark photons, scalar field/dilaton dark matter, and exotic axion–electromagnetic couplings motivated by quantum electromagnetodynamics. The exclusion limits placed on these various dark matter candidates are computed by ORGAN 1a, and sensitivity for some future ORGAN phases are projected. In particular, the dark photon limits are the most sensitive to date in some regions of the parameter space.

Multiple-cell cavity design for high mass axion searches: An extended study

The invisible axion is a well-motivated hypothetical particle which could address two fundamental questions in modern physics—the CP symmetry problem in the strong interactions and the dark matter mystery of our universe. The plausible mass (frequency) range of the QCD axion as a dark matter candidate spans from μeV to meV (O(GHz) to O(THz)). The axion haloscope using a resonant cavity has provided the most sensitive search method in the microwave region. However, experimental searches have been limited to relatively low mass regions mainly due to the reduced cavity volume at high masses. As an effective approach for high-mass axion searches, a unique cavity design, featured by multiple identical cells divided by equidistant thin metal partitions in a single cylindrical cavity, was proposed and successfully demonstrated. We perform an extended study to characterize the multiple-cell cavity design and discuss the various advantages it offers for high-mass axion searches.

Post-inflationary axions: a minimal target for axion haloscopes

An axion-like-particle (ALP) in the post-inflationary scenario with domain wall number N > 1 can be dark matter if the residual ℤN symmetry has a small explicit breaking. Although we cannot determine the full dynamics of the system reliably, we provide evidence that such an ALP can account for the observed dark matter abundance while having a relatively small decay constant and consequently a possibly large coupling to photons. In particular, we determine the number of domain walls per Hubble patch around the time when they form using numerical simulations and combine this with analytic expectations about the subsequent dynamics. We show that the strongest constraint on the decay constant is likely to come from the dark matter ALPs being produced with large isocurvature fluctuations at small spatial scales. We also comment on the uncertainties on the dark matter small-scale structure that might form from these overdensities, in particular pointing out the importance of quantum pressure in the N = 1 case.

Speeding axion haloscope experiments using heterodyne-variance-based detection with a power meter

We describe a new axion search method based on measuring the variance in the interference of the axion signal using injected photons with a power detector. The need for a linear amplifier is eliminated by putting a strong signal into the microwave cavity, to acquire not only the power excess but also measure the variance of the output power. The interference of the external photons with the axion to photon converted signal greatly enhances the variance at the particular axion frequency, providing evidence of its existence. This method has an advantage in that it can always obtain sensitivity near the quantum noise limit even for a power detector with high dark count rate. We describe the basic concept of this method both analytically and numerically, and we show experimental results using a simple demonstration circuit.

Axion haloscope signal power from reciprocity

Axion haloscopes search for dark matter axions from the galactic halo, most commonly by measuring a power excess sourced by the axion effective current density. Constraining axion parameters from detection or lack thereof requires estimating the expected signal power. Often, this is done by studying the response of the haloscope to a known, but different, source current density, for example via a reflection measurement. However, only in the special case when both sources induce the same electromagnetic fields, do the quantities derived from a reflection measurement adequately describe the setup during an axion measurement. While this might be valid for the traditional resonant cavity haloscope, new broadband or open designs like dish antennas or dielectric haloscopes cannot make this assumption. A more general relation between axion- and reflection-induced fields is needed. In this article, we use the Lorentz reciprocity theorem to derive an expression for the axion signal power which instead of the unmeasurable axion-induced fields depends on the measurable reflection-induced fields. This entirely circumvents the need to know the response of the haloscope to the unknown axion source. It applies to a wide variety of haloscopes including resonant cavities, dielectric haloscopes, and broadband dish antennas.

Analysis of Dark Matter Candidates and Detection Scenarios

In recent years, the observations collected by the state-of-art detectors have shown that there is considerable amount of invisible matter in our universe, which is named as dark matter. The study of dark matter has become one of the main research directions nowadays. Contemporarily, there are many particle models are considered as candidate of dark matter, including the models of axion, sterile neutrino, and Weakly Interacting Massive Particle (WIMP) e.g., inert Higgs boson, lightest Kaluza-Klein particle and neutralino in supersymmetry. Furthermore, there are also many experiments and measurements of axions and WIMPs, including axion haloscope ADMX, axion helioscope CAST, and WIMP nuclear recoil detection experiments, such as LUX-ZEPLIN and DarkSide-50. In this paper, the basic model of above candidates will be introduced. In addition, discussion about the additional parity-like symmetry for WIMP model building, shortage of the experiments and the future upgraded dark matter experiments will also be presented. Overall, these results shed light on guiding further exploration of dark matter detection and searching.

Exploration of Wire Array Metamaterials for the Plasma Axion Haloscope

AbstractA plasma haloscope has recently been proposed as a feasible approach to extend the search for dark matter axions above 10 GHz (≈40 eV), whereby the microwave cavity in a conventional axion haloscope is supplanted by a wire array metamaterial. Since the plasma frequency of a metamaterial is determined by its unit cell, and is thus a bulk property, a metamaterial resonator of any frequency can be made arbitrarily large, in contrast to a microwave cavity which incurs a steep penalty in volume with increasing frequency. To assess the actual potential of this concept as a practical dark matter haloscope, the basic properties of wire array metamaterials have been investigated through an extensive series of S21 measurements in the 10 GHz range. This report presents some new systematics of wire array metamaterials themselves including the approach to full plasmonic behavior, the applicability of the semianalytic theory of Belov, and estimates of the loss term which bode favorably for the plasmonic haloscope application. This present work constitutes the first precision test of the semianalytic theory of Belov et al., for which the predicted plasma frequency agrees with the experimental value at the 0.1% level.

Axion haloscope using an 18 T high temperature superconducting magnet

We report details on the axion dark matter search experiment that uses the new technologies of a high-temperature superconducting (HTS) magnet and a Josephson parametric converter (JPC). An 18 T HTS solenoid magnet is developed for this experiment. The JPC is used as the first stage amplifier to achieve a near quantum-limited low-noise condition. A first dark-matter axion search was performed with the 18 T axion haloscope [Youngjae Lee et al., Phys. Rev. Lett. 128, 241805 (2022)]. The scan frequency range is from 4.7789 GHz to 4.8094 GHz (30.5 MHz range). No significant signal consistent with Galactic dark matter axion is observed. Our results set the best limit of the axion-photon-photon coupling (${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$) in the axion mass range of $19.764--19.890\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{eV}$. Using the Bayesian method, the upper bounds of ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$ are set at $0.98\ifmmode\times\else\texttimes\fi{}|{g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}^{\mathrm{KSVZ}}|$ ($1.11\ifmmode\times\else\texttimes\fi{}|{g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}^{\mathrm{KSVZ}}|$) in the mass ranges of $19.764--19.771\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{eV}$ (19.863 to $19.890\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{eV}$), and at $1.76\ifmmode\times\else\texttimes\fi{}|{g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}^{\mathrm{KSVZ}}|$ in the mass ranges of $19.772--19.863\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{eV}$ with 90% confidence level, respectively. We report design, construction, operation, and data analysis of the 18 T axion haloscope experiment.

Simulation of Dielectric Axion Haloscopes with Deep Neural Networks: A Proof-of-Principle

Dielectric axion haloscopes, such as the Madmax experiment, are promising concepts for the direct search for dark matter axions. A reliable simulation is a fundamental requirement for the successful realisation of the experiments. Due to the complexity of the simulations, the demands on computing resources can quickly become prohibitive. In this paper, we show for the first time that modern deep learning techniques can be applied to aid the simulation and optimisation of dielectric haloscopes.

Search for Dark Matter Axions with CAST-CAPP

The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole magnet, has searched for axions in the 19.74 μeV to 22.47 μeV mass range. The detection concept follows the Sikivie haloscope principle, where Dark Matter axions convert into photons within a resonator immersed in a magnetic field. The CAST-CAPP resonator is an array of four individual rectangular cavities inserted in a strong dipole magnet, phase-matched to maximize the detection sensitivity. Here we report on the data acquired for 4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning mechanism of 10 MHz/ min between 4.774 GHz and 5.434 GHz. In the present work, we exclude axion-photon couplings for virialized galactic axions down to gaγγ = 8 × 10−14 GeV−1 at the 90% confidence level. The here implemented phase-matching technique also allows for future large-scale upgrades.

Comparing Instrument Spectral Sensitivity of Dissimilar Electromagnetic Haloscopes to Axion Dark Matter and High Frequency Gravitational Waves

It is known that haloscopes that search for dark matter axions via the axion-photon anomaly are also sensitive to gravitational radiation through the inverse Gertsenshtein effect. Recently this way of searching for high frequency gravitational waves has gained momentum as it has been shown that the strain sensitivity of such detectors, are of the same order of sensitivity to the axion-photon theta angle. Thus, after calculating the sensitivity of a haloscope to an axion signal, we also have calculated the order of magnitude sensitivity to a gravitational wave signal of the same spectral and temporal form. However, it is unlikely that a gravitational wave and an axion signal will be of the same form, since physically the way the signals are generated are completely different. For gravitational wave detection, the spectral strain sensitivity is in units strain per square root Hz, is the natural way to compare the sensitivity of gravitational wave detectors due to its independence on the gravitational wave signal. In this work, we introduce a systematic way to calculate the spectral sensitivity of an axion haloscope, so instrument comparison may be achieved independent of signal assumptions and only depends on the axion to signal transduction sensitivity and noise in the instrument. Thus, the calculation of the spectral sensitivity not only allows the comparison of dissimilar axion detectors independent of signal, but also allows us to compare the order of magnitude gravitational wave sensitivity in terms of spectral strain sensitivity, allowing comparisons to standard gravitational wave detectors based on optical interferometers and resonant-mass technology.

A high-Q superconducting toroidal medium frequency detection system with a capacitively adjustable frequency range >180 kHz.

We describe a newly developed polytetrafluoroethylene/copper capacitor driven by a cryogenic piezoelectric slip-stick stage and demonstrate with the chosen layout cryogenic capacitance tuning of ≈60 pF at ≈10 pF background capacitance. Connected to a highly sensitive superconducting toroidal LC circuit, we demonstrate tuning of the resonant frequency between 345 and 685kHz, at quality factors Q > 100 000. Connected to a cryogenic ultra low noise amplifier, a frequency tuning range between 520 and 710kHz is reached, while quality factors Q > 86 000 are achieved. This new device can be used as a versatile image current detector in high-precision Penning-trap experiments or as an LC-circuit-based haloscope detector to search for the conversion of axion-like dark matter to radio-frequency photons. This new development increases the sensitive detection bandwidth of our axion haloscope by a factor of ≈1000.

Duality-symmetric axion electrodynamics and haloscopes of various geometries

Within the dual symmetric point of view, the theory for seeking axion dark matter via haloscope experiments is derived by exactly solving the dual symmetric axion electrodynamics equation. Notwithstanding that the conventional theory of axion electrodynamics presented in [9,11] is more commonly used in haloscope theory, we show that the dual symmetric axion electrodynamics has more advantages to apply into haloscope theory. First, the dual symmetric and conventional perspective of axion electrodynamics coincide under long-wavelength approximation. Moreover, dual symmetric theory can obtain an exact analytical expression of the axion-induced electromagnetic field for any states of axion. This solution has been used in conventional theory for long-wavelength approximation. The difference between two theories can occur in directional axion detection or electric sensing haloscopes. For illustrative purposes, we consider the various type of resonant cavities: cylindrical solenoid, spherical solenoid, two-parallel-sheet cavity, toroidal solenoid with a rectangular cross-section, and with a circular cross-section. The resonance of the axion-induced signal as well as the ratio of the energy difference over the stored energy inside the cavity are investigated in these types of cavity.

Novel Search for High-Frequency Gravitational Waves with Low-Mass Axion Haloscopes.

Gravitational waves (GWs) generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. We discuss this phenomenon with a particular focus on reinterpreting the results of axion haloscopes based on lumped-element detectors, which probe GWs in the 100kHz-100MHz range. Measurements from ABRACADABRA and SHAFT already place bounds on GWs, although the present strain sensitivity is weak. However, we demonstrate that the sensitivity scaling with the volume of such instruments is significant-faster than for axions-and so rapid progress will be made in the future. With no modifications, DMRadio-m^{3} will have a GW strain sensitivity of h∼10^{-20} at 200MHz. A simple modification of the pickup loop used to readout the induced magnetic flux can parametrically enhance the GW sensitivity, particularly at lower frequencies.

Direct search for dark matter axions excluding ALP cogenesis in the 63- to 67-μeV range with the ORGAN experiment.

The standard model axion seesaw Higgs portal inflation (SMASH) model is a well-motivated, self-contained description of particle physics that predicts axion dark matter particles to exist within the mass range of 50 to 200 micro–electron volts. Scanning these masses requires an axion haloscope to operate under a constant magnetic field between 12 and 48 gigahertz. The ORGAN (Oscillating Resonant Group AxioN) experiment (in Perth, Australia) is a microwave cavity axion haloscope that aims to search the majority of the mass range predicted by the SMASH model. Our initial phase 1a scan sets an upper limit on the coupling of axions to two photons of ∣gaγγ∣ ≤ 3 × 10−12 per giga–electron volts over the mass range of 63.2 to 67.1 micro–electron volts with 95% confidence interval. This highly sensitive result is sufficient to exclude the well-motivated axion-like particle cogenesis model for dark matter in the searched region.

High- Q Microwave Dielectric Resonator for Axion Dark-Matter Haloscopes

The frequency band 1--15 GHz provides exciting prospects for resonant axion haloscopes as indicated by cosmological and astrophysical arguments. Among the challenges currently addressed to reach the required sensitivity, the development of high-quality factor cavities that tolerate multitesla fields plays a central role. We report a three-dimensional resonator based on a right-circular copper cavity with hollow cylinders that confine higher-order modes around the cylinder axis. Its effective volume at 10.3 GHz is $3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ l, and under an 8-T field we measure an internal quality factor of more than nine million. A fine-tuning system limited to approximately $1$-MHz range is tested, useful for understanding the conditions required to run a haloscope with a cavity exceeding the axion quality factor.The cavity parameters we report demonstrate the potential of this unique resonator to probe galactic dark-matter axion at scan rates exceeding 2 MHz/day when the cavity is readout by a quantum-limited receiver.

Fast DAQ system with image rejection for axion dark matter searches

A fast data acquisition (DAQ) system for axion dark matter searches utilizing a microwave resonant cavity, also known as axion haloscope searches, has been developed with a two-channel digitizer that can sample 16-bit amplitudes at rates up to 180 MSamples/s. First, we realized a practical DAQ efficiency of greater than 99% for a single DAQ channel, where the DAQ process includes the online fast Fourier transforms (FFTs). Using an IQ mixer and two parallel DAQ channels, we then also implemented a software-based image rejection without losing the DAQ efficiency. This work extends our continuing effort to improve the figure of merit in axion haloscope searches, the scanning rate.

Axion haloscope array with PT symmetry

We generalize the recently proposed $\mathcal{P T}$-symmetric axion haloscope to a larger array with more $\mathcal{P T}$-symmetric structures. By broadening the response bandwidth of the signal without increasing the readout noise, the optimized scan rate of the axion haloscope is significantly enhanced, as well as is the signal power. Furthermore, we show that the robustness of the detector towards the variations of the array coupling is the strongest when a binary tree structure is introduced which contains a largely enhanced $\mathcal{P T}$ symmetry. The multiple allowed probing sensors can further increase the scan rate by a factor of the sensors' number due to the correlation of the signals. This type of array can strongly boost the search for an axion compared to single-mode resonant detection. The enhancement to the scan rate becomes the most manifest when applied to the proposed detection using a superconducting radio-frequency cavity with an ac magnetic field where most of the parameter space of the QCD axion above kHz can be probed.

Analytical considerations for optimal axion haloscope design

Abstract The cavity haloscope provides a highly sensitive method to search for dark matter axions in the microwave regime. Experimental attempts to enhance the sensitivity have focused on improving major aspects, such as producing strong magnetic fields, increasing cavity quality factors, and achieving lowest possible noise temperatures. Minor details, however, also need to be carefully considered in realistic experimental designs. They are associated with non-uniform magnetic fields over the detection volume, noise propagation under attenuation and temperature gradients, and thermal disequilibrium in the cavity system. We take analytical approaches to these topics and offer optimal treatments for improved performance.