Search

Current and future searches for dark matter axions, based on their resonant conversion to photons in a magnetic field, span many orders of magnitude. A major impediment to designing resonators at the high end of this range, 5 GHz and above, is the proliferation of TE modes, which overwhelm and hybridize with the TM010 mode to which the axion couples, making the search impossible. We demonstrate that a photonic band gap structure can be designed that completely suppresses the TE spectrum, even reducing the number of lattice periods to two or one, and violating perfect lattice symmetry. This allows tunable resonators to be designed in a convenient, volumetrically efficient circular geometry thus enabling future searches in the post-inflation axion mass range.

This Letter reports new results from the HAYSTAC experiment's search for dark matter axions in our galactic halo. It represents the widest search to date that utilizes squeezing to realize sub-quantum limited noise. The new results cover 1.71 $\mu$eV of newly scanned parameter space in the mass ranges 17.28--18.44 $\mu$eV and 18.71--19.46 $\mu$eV. No statistically significant evidence of an axion signal was observed, excluding couplings $|g_\gamma|\geq$ 2.75$\times$$|g_{\gamma}^{\text{KSVZ}}|$ and $|g_\gamma|\geq$ 2.96$\times$$|g_{\gamma}^{\text{KSVZ}}|$ at the 90$\%$ confidence level over the respective region. By combining this data with previously published results using HAYSTAC's squeezed state receiver, a total of 2.27 $\mu$eV of parameter space has now been scanned between 16.96--19.46 $\mu$eV, excluding $|g_\gamma|\geq$ 2.86$\times$$|g_{\gamma}^{\text{KSVZ}}|$ at the 90$\%$ confidence level. These results demonstrate the squeezed state receiver's ability to probe axion models over a significant mass range while achieving a scan rate enhancement relative to a quantum-limited experiment., Comment: 6 pages, 3 figures

DMRadio-m$^3$ is an experiment that is designed to be sensitive to KSVZ and DFSZ QCD axion models in the 10-200 MHz (41 neV$/c^2$ - 0.83 $\mu$eV/$c^2$) range. The experiment uses a solenoidal dc magnetic field to convert an axion dark-matter signal to an ac electromagnetic response in a coaxial copper pickup. The current induced by this axion signal is measured by dc SQUIDs. In this work, we present the electromagnetic modeling of the response of the experiment to an axion signal over the full frequency range of DMRadio-m$^3$, which extends from the low-frequency, lumped-element limit to a regime where the axion Compton wavelength is only a factor of two larger than the detector size. With these results, we determine the live time and sensitivity of the experiment. The primary science goal of sensitivity to DFSZ axions across 30-200 MHz can be achieved with a $3\sigma$ live scan time of 3.7 years., Comment: 14 pages, 6 figures

A search for dark matter axions with masses $>10 \mu eV/c^{2}$ has been performed using the HAYSTAC experiment's squeezed state receiver to achieve sub-quantum limited noise. This report includes details of the design and operation of the experiment previously used to search for axions in the mass ranges $16.96-17.12$ and $17.14-17.28 \mu eV/c^{2}$($4.100-4.140$GHz) and $4.145-4.178$GHz) as well as upgrades to facilitate an extended search at higher masses. These upgrades include improvements to the data acquisition routine which have reduced the effective dead time by a factor of 5, allowing for the new region to be scanned $\sim$1.6 times faster with comparable sensitivity. No statistically significant evidence of an axion signal is found in the range $18.44-18.71\mu eV/c^{2}$($4.459-4.523$GHz), leading to an aggregate upper limit exclusion at the $90\%$ level on the axion-photon coupling of $2.06\times g_{\gamma}^{KSVZ}$., Comment: 20 pages, 16 figures

The QCD axion is one of the most compelling candidates to explain the dark matter abundance of the universe. With its extremely small mass ($\ll 1\,\mathrm{eV}/c^2$), axion dark matter interacts as a classical field rather than a particle. Its coupling to photons leads to a modification of Maxwell's equations that can be measured with extremely sensitive readout circuits. DMRadio-m$^3$ is a next-generation search for axion dark matter below $1\,\mu$eV using a $>4$ T static magnetic field, a coaxial inductive pickup, a tunable LC resonator, and a DC-SQUID readout. It is designed to search for QCD axion dark matter over the range $20\,\mathrm{neV}\lesssim m_ac^2\lesssim 800\,\mathrm{neV}$ ($5\,\mathrm{MHz}<\nu<200\,\mathrm{MHz}$). The primary science goal aims to achieve DFSZ sensitivity above $m_ac^2\approx 120$ neV (30 MHz), with a secondary science goal of probing KSVZ axions down to $m_ac^2\approx40\,\mathrm{neV}$ (10 MHz)., Comment: 8 pages, 4 figures. Updated to fix small errors and correct acknowledgements. Updated title and notational clarifications

Axions are well-motivated dark matter candidates with simple cosmological production mechanisms. They were originally introduced to solve the strong CP problem, but also arise in a wide range of extensions to the Standard Model. This Snowmass white paper summarizes axion phenomenology and outlines next-generation laboratory experiments proposed to detect axion dark matter. There are vibrant synergies with astrophysical searches and advances in instrumentation including quantum-enabled readout, high-Q resonators and cavities and large high-field magnets. This white paper outlines a clear roadmap to discovery, and shows that the US is well-positioned to be at the forefront of the search for axion dark matter in the coming decade., Comment: restore and expand author list

A plasma haloscope has recently been proposed as a feasible approach to extend the search for dark matter axions above 10 GHz ($\sim$ 40 $\mu$eV), whereby the microwave cavity in a conventional axion haloscope is supplanted by a wire array metamaterial. As 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. We have investigated the basic properties of wire array metamaterials through $S_{21}$ measurements in the 10 GHz range. Excellent agreement with theoretical models is found, by which we project achievable quality factors to be of order $10^{4}$ in an actual axion search. Furthermore, schemes for tuning the array over a usable dynamic range ($30\%$ in frequency) appear practical from an engineering perspective., Comment: Published in Annalen der Physik

The QCD axion is a leading dark matter candidate that emerges as part of the solution to the strong CP problem in the Standard Model. The coupling of the axion to photons is the most common experimental probe, but much parameter space remains unexplored. The coupling of the QCD axion to the Standard Model scales linearly with the axion mass; therefore, the highly-motivated region 0.4-120 neV, corresponding to a GUT-scale axion, is particularly difficult to reach. This paper presents the design requirements for a definitive search for GUT-scale axions and reviews the technological advances needed to enable this program., Comment: 16 pages, 4 figures