Axion Detection Research Articles

Hardening of TeV gamma spectrum of active galactic nuclei in galaxy clusters by conversions of photons into axionlike particles

A fraction of AGN producing VHE gamma-rays are located in galaxy clusters. The magnetic field present in the intra-cluster medium would lead to conversions of VHE photons into axion-like particles (ALPs), which are a generic prediction of several extensions of the Standard Model. ALPs produced in this way would traverse cosmological distances unaffected by the extragalactic background light at variance with VHE photons which undergo a substantial absorption. Eventually, a nontrivial fraction of ALPs would re-convert into VHE photons in the magnetic field of the Milky Way. This mechanism produces a significant hardening of the VHE spectrum of AGN in galaxy clusters. As a specific example we consider the energy spectra of two observed VHE gamma-ray sources located in galaxy clusters, namely 1ES 0414+009 at redshift z=0.287 and Mkn 501 at z=0.034. We find that the hardening in the observed spectra becomes relevant at E > 1 TeV. The detection of this signature would allow to indirectly probe the existence of ultra-light ALPs with mass m_a < 10^{-8} eV and photon-ALP coupling g_{a gamma} < 10^{-10} GeV^{-1} with the presently operating Imaging Atmospheric Cherenkov Telescopes like H.E.S.S., MAGIC, VERITAS and CANGAROO-III and even more likely with the planned detectors like CTA, HAWC and HiSCORE. An independent laboratory check of ultra-light ALPs invoked in this mechanism can be performed with the planned upgrade of the photon regeneration experiment ALPS at DESY and with the next generation solar axion detector IAXO.

Direct detection of dark matter axions with directional sensitivity

We study the directional effect of the expected axion dark matter signal in a resonant cavity of an axion haloscope detector, for cavity geometries not satisfying the condition that the axion de Broglie wavelength λa is sufficiently larger than the cavity dimensions L for a fully coherent conversion, i.e. λa≳2πL. We focus on long thin cavities immersed in dipole magnets and find, for appropriately chosen cavity lengths, an O(1) modulation of the signal with the cavity orientation with respect the momentum distribution of the relic axion background predicted by the isothermal sphere model for the galactic dark matter halo. This effect can be exploited to design directional axion dark matter detectors, providing an unmistakable signature of the extraterrestrial origin of a possible positive detection. Moreover, the precise shape of the modulation may give information of the galactic halo distribution and, for specific halo models, give extra sensitivity for higher axion masses.

Direct Dark Matter detection with CUORE

The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment to search for neutrinoless double beta decay in 130Te and other rare processes. CUORE is a bolometric detector composed of 988 TeO2 crystals, with the total mass of about 1 tonne. The large detector mass, low backgrounds, and the low energy threshold of a few keV make the experiment well suited for direct detection of galactic dark matter particles and solar axions. We discuss the development of a novel low-energy trigger that enables such searches, and present the preliminary results from a test run with four CUORE-like crystals at Gran Sasso National Laboratory in Italy.

Superconducting quantum interference device as a near-quantum-limited amplifier for the axion dark-matter experiment

We characterized a microstrip superconducting quantum interference device amplifier (MSA) as a function of frequency and temperature. At 40 mK, with optimal current and flux biases, the maximum gain of 20.4 dB was at 620 MHz; the bandwidth was 21 MHz. The minimum noise temperature TN=48±5 mK occurred at 612 MHz, slightly below the frequency of maximum gain. This value of TN is within a factor of 1.6 of the quantum limit TQ=hf/kB (f is frequency) for a linear, phase-preserving amplifier. Incorporating the MSA into the axion detector at the University of Washington will increase the scan rate by two to three orders of magnitude.

Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter

Successful implementation of thermal leptogenesis requires re-heattemperatures TR≳2 × 109 GeV, in apparent conflict with SUSY models with TeV-scale gravitinos, which require much lower TR in order to avoid Big Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark matter can reconcile thermal leptogenesis with the gravitino problem in models with mG̃≳30 TeV, a rather high Peccei-Quinn breaking scaleand an initial mis-alignment angle θi < 1.We calculate axion and axino dark matter production from four sources, and impose BBN constraints on long-lived gravitinos and neutralinos.Moreover, we discuss several SUSY models which naturally have gravitino masses of the order of tens of TeV.We find a reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like lightest neutralino. However, TR ∼ 1010−1012 GeV can easily be achieved in effective SUSY and in models based on mixed moduli-anomaly mediation. Consequences of this scenario include: 1. an LHC SUSY discovery should be consistentwith SUSY models with a large gravitino mass,2. an apparent neutralino relic abundance ΩZ̃1h2≲1,3. no WIMP direct or indirect detection signals should be found, and 4. the axion mass should be less than ∼ 10−6 eV, somewhat below the conventional range which is explored by microwave cavity axion detection experiments.

Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB

Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB) generally give rise to a neutral wino as a WIMP cold dark matter (CDM) candidate, whose thermal abundance is well below measured values. Here, we investigate four scenarios to reconcile AMSB dark matter with the measured abundance: 1. non-thermal wino production due to decays of scalar fields (e.g. moduli), 2. non-thermal wino production due to decays of gravitinos, 3. non-thermal wino production due to heavy axino decays, and 4. the case of an axino LSP, where the bulk of CDM is made up of axions and thermally produced axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured DM abundance, and we investigate wino-like WIMP direct and indirect detection rates. Wino direct detection rates can be large, and more importantly, are bounded from below, so that ton-scale noble liquid detectors should access all of parameter space for mZ̄1≲500 GeV. Indirect wino detection rates via neutrino telescopes and space-based cosmic ray detectors can also be large. In case 3, the DM would consist of an axion plus wino admixture, whose exact proportions are very model dependent. In this case, it is possible that both an axion and a wino-like WIMP could be detected experimentally. In case 4., we calculate the re-heat temperature of the universe after inflation. In this case, no direct or indirect WIMP signals should be seen, although direct detection of relic axions may be possible. For each DM scenario, we show results for the minimal AMSB model, as well as for the hypercharged and gaugino AMSB models.

Cosmological consequences of Yukawa-unified SUSY with mixed axion/axino cold and warm dark matter

Supersymmetric models with t−b−τ Yukawa unification at MGUTqualitatively predict a sparticle mass spectrum including first and second generation scalarsat the 3–15 TeV scale, third generation scalars at the (few) TeV scale and gluinos in the sub-TeV range. The neutralino relic density in these models typically turns out to lie far abovethe measured dark matter abundance, prompting the suggestion that instead dark matter is composed of an axion/axino mixture.We explore the axion and thermal and non-thermal axino dark matter abundance in Yukawa-unified SUSY models. We find in this scenario that (i) rather large values of Peccei-Quinn symmetry breaking scale fa ∼ 1012 GeV are favored and (ii) rather large values of GUT scale scalar masses ∼ 10−15 TeV allow for the re-heat temperature TR of the universe to be TR ⪆ 106 GeV. This allows in turn a solution to the gravitino/Big Bang Nucleosynthesis problem while also allowing for baryogenesis via non-thermal leptogenesis. The large scalar masses for Yukawa-unified models are also favored by data on b → sγ and Bs → μ+μ− decay.Testable consequences from this scenario include a possible axion detection at axion search experiments, but null results from direct and indirect WIMP search experiments.

Dilatonic dark matter and its experimental detection

Assuming that the dilaton is the dark matter of the Universe, we propose an experiment to detect the relic dilaton using the electromagnetic resonant cavity, based on the dilaton-photon conversion in strong electromagnetic background. We calculate the density of the relic dilaton, and estimate the dilaton mass for which the dilaton becomes the dark matter of the Universe. With this we calculate the dilaton detection power in the resonant cavity, and compare it with the axion detection power in a similar resonant cavity experiment.

Collective two-atom effects and trapping states in the micromaser

We investigate signals of trapping states in the micromaser system in terms of the average number $⟨n⟩$ of cavity photons as well as a suitably defined correlation length of atoms leaving the cavity. In the description of collective two-atom effects we allow the mean number, $ϵ$, of pump atoms inside the cavity during the characteristic atomic cavity transit time to be as large as of order one. The master equation we consider, which describes the micromaser including collective two-atom effects, still exhibits trapping states for $ϵ\ensuremath{\ne}0$, even for a mean number of atoms inside the cavity close to one. We, however, argue more importantly that the trapping states are more pronounced in terms of the correlation length as compared to $⟨n⟩$, i.e., we suggest that trapping states can be more clearly revealed experimentally in terms of the atom correlation length. For axion detection in the micromaser this observable may, therefore, be an essential ingredient.

Search for axions

A short introduction to the axion physics is given. Some approaches of detection of (solar) axions or other exotic particles with similar couplings are presented. The references should be consulted for further reading.

A search for solar hadronic axions using 83Kr

We introduce a new experimental method for solar hadronic axions search. It is suggested that these axions are created in the Sun during M1 transition between the first thermally excited level at 9.4 keV and the ground state in $^{83}Kr$. Our method is based on axion detection via resonant absorption process by the same nucleus in the laboratory. We use proportional gas counter filled with krypton to detect signals for axions. With this setup, target and detector are the same which increases the efficiency of the experiment. At present, an upper limit on hadronic axion mass of 5.5 keV at the 95% confidence level is obtained.

Superconducting quantum interference device amplifiers at gigahertz frequencies

A series of five dc superconducting quantum interference devices (SQUIDs) have been operated as microstrip amplifiers at frequencies ranging from 2.2 to 7.4 GHz. In these devices, the signal is connected between the SQUID washer and coil, which acts as a microstrip resonator. The gain measured at 4.2 K ranged from 12±1 to 6±1 dB. The noise temperature of three devices at 4.2 K in the frequency range 2.2–4 GHz was between 1 and 2 K, and the saturation temperature was between 150 and 250 K. Applications of these devices include readout for axion detectors, and intermediate-frequency amplifiers for superconductor–insulator–superconductor and hot-electron bolometer mixers.

Large-scale microwave cavity search for dark-matter axions

We have built and operated a large-scale axion detector, based on a method originally proposed by Sikivie, to search for halo axions. The apparatus consists of a cylindrical tunable high-Q microwave cavity threaded axially by a static high magnetic field. This field stimulates axions that enter the cavity to convert into single microwave photons. The conversion is resonantly enhanced when the cavity resonant frequency is near the axion rest mass energy. The experiment is cooled to 1.5 K and the electromagnetic power spectrum emitted by the cavity is measured by an ultra-low-noise microwave receiver. The axion would be detected as excess power in a narrow line within the cavity resonance. The apparatus has achieved a power sensitivity better than ${10}^{\ensuremath{-}23} \mathrm{W}$ in the mass range $2.9--3.3 \ensuremath{\mu}\mathrm{eV}.$ For the first time the rf cavity technique has explored plausible axion models, assuming axions make up a significant fraction of the local halo density. The experiment continues to operate and will explore a large part of the mass in the range of $1--10 \ensuremath{\mu}\mathrm{eV}$ in the near future. An upgrade of the experiment is planned with dc superconducting quantum interference device microwave amplifiers operating at a lower physical temperature. This next generation detector would be sensitive to even more weakly coupled axions contributing only fractionally to the local halo density.

Cryogenic cavity detector for a large-scale cold dark-matter axion search

An axion detector consisting of a tunable high- Q cavity, a superconducting magnet, and a superheterodyne receiver with an ultra-low noise pre-amplifier has been built to search for galactic halo axions in the mass range of 1.3–13 μeV. The detector instrumentation, search process, and data analysis are described. For the first time, this class of detector has reached sufficient sensitivity to detect halo axions with high confidence.

Niobium dc SQUID with microstrip input coupling as an amplifier for the axion detector

The output from the 1.4 K cavity of the axion detector at Lawrence Livermore National Laboratory is currently amplified by a cooled semiconductor amplifier with a noise temperature of about 3 K. To achieve a lower system noise temperature, one must cool the cavity to a lower temperature and use an amplifier with a lower noise temperature. An amplifier based on a dc SQUID (Superconducting QUantum Interference Device) has been developed in which the input signal is coupled to one end of the microstrip formed by the input coil and the body of the SQUID. Gains of up to 20 dB have been achieved in the frequency range 100–900 MHz. At 4.2 K and with a room-temperature post-amplifier the system noise temperature ranged from 0.5 K ± 0.3 K at 80 MHz to 3.0 K ± 0.7 K at 500 MHz; particularly at the higher frequencies, the measured noise temperature was determined by the noise temperature of the post-amplifier (about 80 K). With the SQUID cooled to 1.8 K and a cooled high electron mobility transistor, the system noise temperature was reduced to 0.3 K ± 0.1 K at 250 MHz and 0.25 K ± 0.1 K at 365 MHz.

Alternatives to axion production and detection

We consider axion production during the formation of a quark-gluon plasma in relativistic heavy-ion collisions and discuss a possible detection scheme.

Large bore high field magnets

The National High Magnetic Field Laboratory (NHMFL) is, as part of its charter with the National Science Foundation (NSF), building several state-of-the-art magnets which exploit the technological limits in field strength and useful volume. Four magnets are of special interest in this context: a 20 T, 200 mm bore resistive magnet, a persistent 21.1 T, 144 mm bore superconducting NMR magnet, a 15 T, 620 mm bore powered superconducting magnet, and a 50 T, 200 mm bore pulse magnet, built in cooperation with LANL. A condensed overview of the NHMFL and a description of its activities in magnet research is given. The path to a magnet optimized for the detection of axions is explored. To this end, the large bore magnets in use or construction at the NHMFL and their different technologies are compared. Design issues of superconducting magnets for reliable operation, an optimization example and a demonstration of the cost constraints follow.

The large scale U.S. dark matter axion search

We describe the instrumentation and operations of the microwave cavity axion detector presently taking data at Lawrence Livermore National Laboratory. This experiment, a collaboration of LLNL, MIT, Univ. of Florida, LBNL, Univ. of Chicago, FNAL, and INR/Moscow, has been operating with greater than 90% live time since February 1996 with the objective of exploring the region from 0.3 to 3.0 GHz (1.2 to 12.4 μeV) at greater than KSVZ sensitivity. In a companion paper (E. Daw) in these proceedings, the data analysis and first results will be described.

On the potential of light-by-light scattering for invisible axion detection

An experimental program is in progress, searching for possible non QED signals in elastic photon-photon scattering in the optical domain[1]. We examine here the potential of this process for the detection of a possible light pseudoscalar such as the axion.

Searching for MACHOs (and Other Dark Matter Candidates) in a Simulated Galaxy

We conduct gravitational microlensing experiments in a galaxy taken from a cosmological N-body simulation. Hypothetical observers measure the optical depth and event rate toward hypothetical LMCs and compare their results with model predictions. Because we control the accuracy and sophistication of the model, we can determine how good it has to be for statistical errors to dominate over systematic ones. Several thousand independent microlensing experiments are performed. When the "best-fit" triaxial model for the mass distribution of the halo is used, the agreement between the measured and predicted optical depths is quite good: by and large, the discrepancies are consistent with statistical fluctuations. If, on the other hand, a spherical model is used, systematic errors dominate. Even with our "best-fit" model, there are a few rare experiments where the deviation between the measured and predicted optical depths cannot be understood in terms of statistical fluctuations. In these experiments there is typically a clump of particles crossing the line of sight to the hypothetical LMC. These clumps can be either gravitationally bound systems or transient phenomena in a galaxy that is still undergoing phase mixing. Substructure of this type, if present in the Galactic distribution of MACHOs, can lead to large systematic errors in the analysis of microlensing experiments. We also describe how hypothetical WIMP and axion detection experiments might be conducted in a simulated N-body galaxy.