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DOE OSTI2024

Axion Dark Matter eXperiment: Run 1A analysis details

The ADMX Collaboration gathered data for its Run 1A axion dark matter search from January 2017 to June 2017, scanning with an axion haloscope over the frequency range 645–680 MHz ( 2.66 – 2.81 μ eV in axion mass) at Dine-Fischler-Srednicki-Zhitnitskii (DFSZ) sensitivity. The resulting axion search found no axionlike signals comprising all the dark matter in the form of a virialized galactic halo over the entire frequency range, implying lower bound exclusion limits at or below DFSZ coupling at the 90% confidence level. This paper presents expanded details of the axion search analysis of Run 1A, including review of relevant experimental systems, data-taking operations, preparation and interpretation of raw data, axion search methodology, candidate handling, and final axion limits. Published by the American Physical Society 2024

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Neutron star cooling with lepton-flavor-violating axions

The cores of dense stars are a powerful laboratory for studying feebly coupled particles such as axions. Some of the strongest constraints on axionlike particles and their couplings to ordinary matter derive from considerations of stellar axion emission. In this work we study the radiation of axionlike particles from degenerate neutron star matter via a lepton-flavor-violating coupling that leads to muon-electron conversion when an axion is emitted. We calculate the axion emission rate per unit volume (emissivity) and by comparing with the rate of neutrino emission, we infer upper limits on the lepton-flavor-violating coupling that are at the level of | g a e μ | ≲ 10 − 6 . For the hotter environment of a supernova, such as SN 1987A, the axion emission rate is enhanced and the limit is stronger, at the level of | g a e μ | ≲ 10 − 11 , competitive with laboratory limits. Interestingly, our derivation of the axion emissivity reveals that axion emission via the lepton-flavor-violating coupling is suppressed relative to the familiar lepton-flavor-preserving channels by the square of the plasma temperature to muon mass ratio, which is responsible for the relatively weaker limits. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2025

High-quality axions from higher-form symmetries in extra dimensions

The extradimensional axion solves the strong C P problem while largely circumventing the quality problem that plagues its four-dimensional counterparts. Such high quality can be clearly understood in terms of the generalized global symmetries of the higher-dimensional theory. We emphasize that an electric one-form symmetry is entirely responsible for protecting the potential of axions arising from 5D gauge theories and use this to systematically characterize the extradimensional axion quality problem. We identify three ways of breaking this one-form symmetry to generate an axion potential: adding electrically charged matter, gauging a magnetic higher-form symmetry, and turning on an Adler-Bell-Jackiw anomaly. In the latter case, we identify new ways of generating an axion potential via extradimensional magnetic monopoles. We also discuss how the axion is modified if the protective electric one-form symmetry is itself gauged. Finally, we relate these effects to gravitational expectations for the quality problem via generalized weak gravity conjectures. The clarity that generalized symmetries bring to the extradimensional axion quality problem highlights their relevance to particle phenomenology. Published by the American Physical Society 2025

Craig, Nathaniel↗
DOE OSTI2025

Nuclear spin metrology with nitrogen vacancy center in diamond for axion dark matter detection

We present a method to directly detect the axion dark matter using nitrogen vacancy centers in diamonds. In particular, we use metrology leveraging the nuclear spin of nitrogen to detect axion-nucleus couplings. This is achieved through protocols designed for dark matter searches, which introduce a novel approach of quantum sensing techniques based on the nitrogen vacancy center. Although the coupling strength of the magnetic fields with nuclear spins is three orders of magnitude smaller than that with electron spins for conventional magnetometry, the axion interaction strength with nuclear spins is the same order of magnitude as that with electron spins. Furthermore, we can take advantage of the long coherence time by using the nuclear spins for the axion dark matter detection. Our method has the potential to be sensitive to a broad frequency range ≲ 100 Hz corresponding to the axion mass m a ≲ 4 × 10 − 13 eV . We present the detection limit of our method for both the axion-neutron and the axion-proton couplings and discuss its significance in comparison with other proposed ideas. We also show that the sensitivities of the NV center sensor to various spin species will open up new directions for constructing protocols that can mitigate magnetic noise effects. Published by the American Physical Society 2025

Chigusa, So (ORCID:0000000160054447)↗
DOE OSTI2025

Daily modulations and broadband strategy in axion searches: An application with the CAST-CAPP detector

It has been previously advocated that the presence of the daily and annual modulations of the axion flux on the Earth’s surface may dramatically change the strategy of the axion searches. The arguments were based on the so-called Axion Quark Nugget (AQN) dark matter model which was originally put forward to explain the similarity of the dark and visible cosmological matter densities Ω dark ∼ Ω visible . In this framework, the population of galactic axions with mass 10 − 6 eV ≲ m a ≲ 10 − 3 eV and velocity ⟨ v a ⟩ ∼ 10 − 3 c will be accompanied by axions with typical velocities ⟨ v a ⟩ ∼ 0.6 c emitted by AQNs. Furthermore, in this framework, it has also been argued that the AQN-induced axion daily modulation (in contrast with the conventional weakly interactive massive particle paradigm) could be as large as (10–20)%, representing the main motivation for the present investigation. We argue that the daily modulations along with the broadband detection strategy can be very useful tools for the discovery of such relativistic axions. The data from the CAST-CAPP detector have been used following such arguments. Unfortunately, due to the dependence of the amplifier chain on temperature-dependent gain drifts and other factors, we could not conclusively show the presence or absence of a dark sector-originated daily modulation. However, this proof of principle analysis procedure can serve as a reference for future studies. Published by the American Physical Society 2025

Caspers, F.↗
DOE OSTI2016

Modulation sensitive search for nonvirialized dark-matter axions

Nonvirialized dark-matter axions may be present in the Milky Way halo in the form of low-velocity-dispersion flows. In this paper, the Axion Dark-Matter eXperiment performed a search for the conversion of these axions into microwave photons using a resonant cavity immersed in a strong, static magnetic field. The spread of photon energy in these measurements was measured at spectral resolutions of the order of 1 Hz and below. If the energy variation were this small, the frequency modulation of any real axion signal due to the orbital and rotational motion of Earth would become non-negligible. Conservative estimates of the expected signal modulation were made and used as a guide for the search procedure. The photon frequencies covered by this search are 812–852 and 858–892 MHz, which correspond to an axion mass of 3.36–3.52 and 3.55 – 3.69 μ eV . Finally, no axion signal was found, and limits were placed on the maximum local density of nonvirialized axions of these masses.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Axion Perturbations: A General Analytical Treatment

Cosmological data provides us two key constraints on dark matter (DM): it must have a particular abundance, and it must have an adiabatic spectrum of density perturbations in the early universe. Many different cosmological scenarios have been proposed that establish the abundance of axion DM in qualitatively different ways. In this paper we emphasize that, despite this variety of backgrounds, the perturbations in axion DM can be understood from universal principles. How does a feebly interacting axion field acquire perturbations proportional to those of photons? How do the isocurvature power spectrum and non-Gaussianity depend on the background evolution of the universe? We answer these questions for a completely general choice of cosmological background and temperature-dependent axion potential. We show that the most general solution to the axion field equation on super-horizon scales is entirely determined by the family of background solutions for different initial field values . This holds for both the component in the field perturbation solution contributing to the DM isocurvature perturbation (enhanced at late times by the sensitivity of the DM abundance to the initial condition, , which can be large for initial conditions near the hilltop), and the other component that contributes to the DM curvature perturbation. In particular, we explain that an unperturbed axion field in the early universe evolving into one with nontrivial adiabatic perturbations is guaranteed by Weinberg's theorem on adiabatic modes. These results have been derived before with various assumptions, such as a radiation dominated background or a quadratic potential. Our aim is to give a clear, simple derivation that is manifestly independent of those assumptions, and thus can be applied to any cosmological axion scenario.

Cosmology and Nongalactic Astrophysics (astro-ph.C↗
NASA NTRS1989

Windows on the axion

Peccei-Quinn symmetry with attendant axion is a most compelling, and perhaps the most minimal, extension of the standard model, as it provides a very elegant solution to the nagging strong CP-problem associated with the theta vacuum structure of QCD. However, particle physics gives little guidance as to the axion mass; a priori, the plausible values span the range: 10(-12)eV is approx. less than m(a) which is approx. less than 10(6)eV, some 18 orders-of-magnitude. Laboratory experiments have excluded masses greater than 10(4)eV, leaving unprobed some 16 orders-of-magnitude. Axions have a host of interesting astrophysical and cosmological effects, including, modifying the evolution of stars of all types (our sun, red giants, white dwarfs, and neutron stars), contributing significantly to the mass density of the Universe today, and producting detectable line radiation through the decays of relic axions. Consideration of these effects has probed 14 orders-of-magnitude in axion mass, and has left open only two windows for further exploration: 10(-6)eV is approx. less than m(a) is approx. less than 10(-3)eV and 1eV is approx. less than m(a) is approx. less than 5eV (hadronic axions only). Both these windows are accessible to experiment, and a variety of very interesting experiments, all of which involve heavenly axions, are being planned or are underway.

Turner, Michael S.↗
NASA NTRS1993

Constraints on axions from the extragalactic background light

We consider the effect of dark matter in the form of multi-eV axions on the extragalactic background light. Our treatment differs from that of other workers in that we assume axions to be clustered in Galactic halos, with nonzero velocity dispersions. We also approach the problem in a fully general relativistic manner, treating the axion halos as luminous elements of a pressure-free perfect fluid in a standard Friedmann-Robertson-Walker universe. We find that the ultraviolet extragalactic background light places a firm upper limit of 9 eV on the axion rest energy, and that this drops to 4 eV for the simplest axion models, all but closing the multi-eV axion window (which begins at 3 eV). These results are close to earlier upper limits of 5 and 8 eV derived from the extragalactic background by Turner and Ressell, respectively. Although our methods differ somewhat from theirs, our findings support their conclusion that axions, if they exist, are likely to have rest energies well below the eV range.

Overduin, J. M.↗
DOE OSTI2025

Constraints on light QCD and CP-violating axions from the death line of rotation-powered pulsars

For axions that couple to nucleons, the presence of dense nuclear matter can displace the axion from its vacuum minimum, sourcing large field gradients around neutron stars (and, more generally, compact objects). These gradients, which we refer to as axion hair, couple to the local background magnetic field, inducing a large voltage drop near the surface of the star; here, we demonstrate that the presence of axion hair decouples local near-field particle acceleration in the open magnetic field line bundle from the rotational frequency of the pulsar itself. This is significant as the non-observation of old slowly-rotating pulsars is attributed to the fact the rotationally-induced electric fields are not strong enough to sustain $e^\pm$ pair production. In this work, we review the evidence for the existence for `pulsar death', i.e. the threshold at which $e^\pm$ pair production (and thus, by association, coherent radio emission) ceases, and demonstrate using both semi-analytics and particle-in-cell simulations that the existence of axion hair can dramatically extend pulsar lifetimes. We show that the non-observation of extremely old, slowly rotating, pulsars allows for a new probe of light QCD and CP-violating axions. We also demonstrate how the observation of emission from both poles of pulsars with nearly orthogonal rotational and magnetic axes, as seen e.g. in PSR J1906+0746, can be used to set competitive limits on CP-violating axion-nucleon interactions.

Witte, Samuel J. [Oxford U., Theor. Phys.; DESY; H↗
DOE OSTI2024

Effects of finite material size on axion-magnon conversion

Magnetic materials are particularly favorable targets for detecting axions interacting with electrons because the collective excitation of electron spins, the magnon, can be excited through the axion-magnon conversion process. It is often assumed that only the zero-momentum uniformly precessing magnetostatic (Kittel) mode of the magnon is excited. This is justified if the de Broglie wavelength of the axion is much longer than the size of the target magnetic material. However, if the de Broglie wavelength is shorter, finite-momentum magnon modes can also be excited. We systematically analyze the target material size dependence of the axion-magnon conversion rate. We discuss the importance of these effects in the detection of relativistic axions as well as in the detection of axion dark matter of relatively heavy mass with large material size.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Electrobaryonic axion: hair of neutron stars

Axion-like particles are predicted in many physics scenarios beyond the Standard Model (SM). Their interactions with SM particles may arise from the triangle anomaly of the associated global symmetry, along with other SM global and gauge symmetries, including anomalies with the global baryon number and electromagnetic gauge symmetries. We initiate the phenomenological study of the corresponding “electrobaryonic axion”—a particle that couples with both the baryon chemical potential and the electromagnetic field. Neutron stars, particularly magnetars, possessing high baryon density and strong magnetic fields, can naturally develop a thin axion hair around their surface. In this study, we calculate this phenomenon, considering the effects of neutron star rotation and general relativity. For axion particles lighter than the neutron star rotation frequency, the anomalous interaction can also induce the emission of axion particles from the neutron star. In the light axion regime, this emission can significantly contribute to the neutron star cooling rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Physical signatures of fermion-coupled axion dark matter

In the presence of axion dark matter, fermion spins experience an “axion wind” torque and an “axioelectric” force. We investigate new experimental probes of these effects and find that magnetized analogs of multilayer dielectric haloscopes can explore orders of magnitude of new parameter space for the axion-electron coupling. We also revisit the calculation of axion absorption into in-medium excitations, showing that axioelectric absorption is screened in spin-polarized targets, and axion wind absorption can be characterized in terms of a magnetic energy loss function. Finally, our detailed theoretical treatment allows us to critically examine recent claims in the literature. We find that axioelectric corrections to electronic energy levels are smaller than previously estimated and that the purported electron electric dipole moment due to a constant axion field is entirely spurious.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Axion domain walls, small instantons, and non-invertible symmetry breaking

Non-invertible global symmetry often predicts degeneracy in axion potentials and carries important information about the global form of the gauge group. When these symmetries are spontaneously broken they can lead to the formation of stable axion domain wall networks which support topological degrees of freedom on their worldvolume. Such non-invertible symmetries can be broken by embedding into appropriate larger UV gauge groups where small instanton contributions lift the vacuum degeneracy, and provide a possible solution to the domain wall problem. We explain these ideas in simple illustrative examples and then apply them to the Standard Model, whose gauge algebra and matter content are consistent with several possible global structures. Each possible global structure leads to different selection rules on the axion couplings, and various UV completions of the Standard Model lead to more specific relations. As a proof of principle, we also present an example of a UV embedding of the Standard Model which can solve the axion domain wall problem. The formation and annihilation of the long-lived axion domain walls can lead to observables, such as gravitational wave signals. Observing such signals, in combination with the axion coupling measurements, can provide valuable insight into the global structure of the Standard Model, as well as its UV completion.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Acoustic misalignment mechanism for axion dark matter

A rotation in the field space of a complex scalar field corresponds to a Bose-Einstein condensation of U(1) charges. We point out that fluctuations in this rotating condensate exhibit sound-wave modes, which can be excited by cosmic perturbations and identified with axion fluctuations once the U(1) charge condensate has been sufficiently diluted by cosmic expansion. We consider the possibility that these axion fluctuations constitute dark matter and develop a formalism to compute its abundance. We carefully account for the growth of fluctuations during the epoch where the complex scalar field rotates on the body of the potential and possible nonlinear evolution when the fluctuations become non-relativistic. We find that the resultant dark matter abundance can exceed the conventional and kinetic misalignment contributions if the radial direction of the complex scalar field is sufficiently heavy. The axion dark matter may also be warm enough to leave imprints on structure formation. We discuss the implications of this novel dark matter production mechanism — acoustic misalignment mechanism — for the axion rotation cosmology, including kination domination and baryogenesis from axion rotation, as well as for axion searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Axion detection via superfluid 3 He ferromagnetic phase and quantum measurement techniques

We propose to use the nuclear spin excitation in the ferromagnetic A 1 phase of the superfluid 3 He for the axion dark matter detection. This approach is striking in that it is sensitive to the axion-nucleon coupling, one of the most important features of the QCD axion introduced to solve the strong CP problem. We review a quantum mechanical description of the nuclear spin excitation and apply it to the estimation of the axion-induced spin excitation rate. We also describe a possible detection method of the spin excitation in detail and show that the combination of the squeezing of the final state with the Josephson parametric amplifier and the homodyne measurement can enhance the sensitivity. It turns out that this approach gives good sensitivity to the axion dark matter with the mass of $\mathcal{O}$(1) μeV depending on the size of the external magnetic field. We estimate the parameters of experimental setups, e.g., the detector volume and the amplitude of squeezing, required to reach the QCD axion parameter space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

New superconducting toroidal magnet system for IAXO, the international AXion observatory

Axions are hypothetical particles that were postulated to solve one of the puzzles arising in the standard model of particle physics, namely the strong CP (Charge conjugation and Parity) problem. The new International AXion Observatory (IAXO) will incorporate the most promising solar axions detector to date, which is designed to enhance the sensitivity to the axion-photon coupling by one order of magnitude beyond the limits of the current state-of-the-art detector, the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field distributed over a very large volume to convert solar axions into X-ray photons. Inspired by the successful realization of the ATLAS barrel and end-cap toroids, a very large superconducting toroid is currently designed at CERN to provide the required magnetic field. This toroid will comprise eight, one meter wide and twenty one meter long, racetrack coils. The system is sized 5.2 m in diameter and 25 m in length. Its peak magnetic field is 5.4 T with a stored energy of 500 MJ. The magnetic field optimization process to arrive at maximum detector yield is described. In addition, materials selection and their structure and sizing has been determined by force and stress calculations. Thermal loads are estimated to size the necessary cryogenic power and the concept of a forced flow supercritical helium based cryogenic system is given. A quench simulation confirmed the quench protection scheme.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Axions and saxions from the primordial supersymmetric plasma and extra radiation signatures

We calculate the rate for thermal production of axions and saxions via scattering of quarks, gluons, squarks, and gluinos in the primordial supersymmetric plasma. Systematic field theoretical methods such as hard thermal loop resummation are applied to obtain a finite result in a gauge-invariant way that is consistent to leading order in the strong gauge coupling. We calculate the thermally produced yield and the decoupling temperature for both axions and saxions. For the generic case in which saxion decays into axions are possible, the emitted axions can constitute extra radiation already prior to big bang nucleosynthesis and well thereafter. We update associated limits imposed by recent studies of the primordial helium-4 abundance and by precision cosmology of the cosmic microwave background and large scale structure. We show that the trend towards extra radiation seen in those studies can be explained by late decays of thermal saxions into axions and that upcoming Planck results will probe supersymmetric axion models with unprecedented sensitivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗