Axion Search Experiments Research Articles

Enhanced photon coupling of ALP dark matter adiabatically converted from the QCD axion

We revisit the adiabatic conversion between the QCD axion and axion-like particle (ALP) at level crossing, which can occur in the early universe as a result of the existence of a hypothetical mass mixing. This is similar to the Mikheyev-Smirnov-Wolfenstein effect in neutrino oscillations. After refining the conditions for the adiabatic conversion to occur, we focus on a scenario where the ALP produced by the adiabatic conversion of the QCD axion explains the observed dark matter abundance. Interestingly, we find that the ALP decay constant can be much smaller than the ordinary case in which the ALP is produced by the realignment mechanism. As a consequence, the ALP-photon coupling is enhanced by a few orders of magnitude, which is advantageous for the future ALP and axion-search experiments using the ALP-photon coupling.

Studies of radioactive background in SOI pixel detector for solar axion search experiment

An application of a modern noble pixel detector, XRPIX series, for solar KSVZ axion search experiment is being developed. A low radioactive background is necessary in the detector volume for the axion search. We surveyed the radioactivity of all peripheral components mounted on the detector using an HPGe detector. The results are used as an input for a GEANT4 Monte Carlo simulation to study the background in the experiment. This paper describes the expected background and the simulated sensitivity of stacked XRPIX detector currently under development.

SQUID amplifiers for axion search experiments

In the experiments for dark-matter QCD-axion searches, very weak microwave signals from a low-temperature High-Q resonant cavity should be detected using the highest sensitivity. The best commercial low-noise cryogenic semiconductor amplifiers based on high electron mobility transistors have a lowest noise temperature above 1.0 K, even if they are cooled well below 1 K. Superconducting quantum interference devices can work as microwave amplifiers with temperature noise close to the standard quantum limit. Previous SQUID-based RF amplifiers designed for axion search experiments have a microstrip resonant input coil and are thus called micro-strip SQUID amplifiers or MSAs. Due to the resonant input coupling they usually have narrow bandwidth. In this paper we report on a SQUID-based wideband microwave amplifier fabricated using sub-micron size Josephson junctions with very low capacitance. A single amplifier can be used in a frequency range of approximately 1–5 GHz.

Development of a Data Acquisition Software for the CULTASK Experiment

Axion is a candidate of dark matter, and is a consequence of a solution to the strong CP problem. CULTASK (CAPP Ultra-Low Temperature Axion Search in Korea) is an axion search experiment which is being developed in Korea. As a part of the project, homegrown software, which governs the data acquisition and control systems, has been developed. The software governs the data acquisition as well as equipment control. In this proceeding, the development of the software is discussed.

Magnetoresistance in copper at high frequency and high magnetic fields

In halo dark matter axion search experiments, cylindrical microwave cavities are typically employed to detect signals from the axion-photon conversion. To enhance the conversion power and reduce the noise level, cavities are placed in strong solenoid magnetic fields at sufficiently low temperatures. Exploring high mass regions in cavity-based axion search experiments requires high frequency microwave cavities and thus understanding cavity properties at high frequencies in extreme conditions is deemed necessary. We present a study of the magnetoresistance of copper using a cavity with a resonant frequency of 12.9 GHz at the liquid helium temperature in magnetic fields up to 15 T utilizing a second generation high temperature superconducting magnet. The observations are interpreted to be consistent with the anomalous skin effect and size effect. This is the first measurement of magnetoresistance at a high frequency (>10 GHz) in high magnetic fields (>10 T).

A Radio Astronomy Search for Cold Dark Matter Axions

Abstract The search for axions has gained ground in recent years, with laboratory searches for cold dark matter (CDM) axions, relativistic solar axions, and ultra-light axions as the subject of extensive literature. In particular, the interest in axions as CDM candidates has been motivated by their potential to account for all of the inferred values of in the standard model. Indeed, the value of could be provided by a light axion. We investigate the possibility of complementing existing axion search experiments with radio telescope observations in an attempt to detect axion conversion in astrophysical magnetic fields. Searching for a CDM axion signal from a large-scale astrophysical environment provides new challenges, with the magnetic field structure playing a crucial role in both the rate of interaction and the properties of the observed photon. However, with a predicted frequency in the radio band (200 MHz–200 GHz) and a distinguishable spectral profile, next-generation radio telescopes may offer new opportunities for detection. The SKA-mid telescope has a planned frequency range of 0.4–13.8 GHz with optimal sensitivity in the range of ∼2–7 GHz. Considering observations at ∼500 MHz, the limiting sensitivity is expected to be ∼0.04 mK based on a 24 hr integration time. This compares with a predicted CDM axion all-sky signal temperature of ∼0.04 mK using SKA Phase 1 telescopes and up to ∼1.17 mK using a collecting area of (1 km)2 as planned for Phase 2.

Beyond WIMPs: the Quark (Anti) Nugget Dark Matter

We review a testable dark matter (DM) model outside of the standard WIMP paradigm. The model is unique in a sense that the observed ratio $\Omega_{\rm dark} \simeq \Omega_{\rm visible}$ for visible and dark matter densities finds its natural explanation as a result of their common QCD origin when both types of matter (DM and visible) are formed during the QCD transition and both are proportional to single dimensional parameter of the system, $\Lambda_{\rm QCD}$. We argue that the charge separation effect also inevitably occurs during the same QCD transition in the presence of the $\cal{CP}$ odd axion field $a(x)$. It leads to preferential formation of one species of nuggets on the scales of the visible Universe where the axion field $a(x)$ is coherent. A natural outcome of this preferential evolution is that only one type of the visible baryons (not anti- baryons) remain in the system after the nuggets complete their formation. Unlike conventional WIMP dark matter candidates, the nuggets and anti-nuggets are strongly interacting but macroscopically large objects. The rare events of annihilation of the anti-nuggets with visible matter lead to a number of observable effects. We argue that the relative intensities for a number of measured excesses of emission from the centre of galaxy (covering more than 11 orders of magnitude) are determined by standard and well established physics. At the same time the absolute intensity of emission is determined by a single new fundamental parameter of the theory, the axion mass, $10^{-6} {\rm eV} \lesssim m_a \lesssim 10^{-3}{\rm eV}$. Finally, we comment on implications of these studies for the axion search experiments, including microwave cavity and the Orpheus experiments.

Axion field and the quark nugget’s formation at the QCD phase transition

We study a testable dark matter (DM) model outside of the standard WIMP paradigm in which the observed ratio $\Omega_{\rm dark} \simeq \Omega_{\rm visible}$ for visible and dark matter densities finds its natural explanation as a result of their common QCD origin when both types of matter (DM and visible) are formed at the QCD phase transition and both are proportional to $\Lambda_{\rm QCD}$. Instead of conventional "baryogenesis" mechanism we advocate a paradigm when the "baryogenesis" is actually a charge separation process which always occur in the presence of the $\cal{CP}$ odd axion field $a(x)$. In this scenario the global baryon number of the Universe remains zero, while the unobserved anti-baryon charge is hidden in form of heavy nuggets, similar to Witten's strangelets and compromise the DM of the Universe. We argue that the nuggets will be inevitably produced during the QCD phase transition as a result of Kibble-Zurek mechanism on formation of the topological defects during a phase transition. Relevant topological defects in our scenario are the closed bubbles made of the $N_{\rm DW}=1$ axion domain walls. These bubbles, in general, accrete the baryon (or anti baryon) charge, which eventually result in formation of the nuggets and anti-nuggets carrying a huge baryon (anti-baryon) charge. The main consequence of the model, $\Omega_{\rm dark} \approx \Omega_{\rm visible}$ is insensitive to the axion mass which may assume any value within the observationally allowed window $10^{-6} {\rm eV} \lesssim m_a \lesssim 10^{-3}{\rm eV}$. We also estimate the baryon to entropy ratio $\eta\equiv {n_B}/{n_{\gamma}}\sim 10^{-10}$ within this scenario. Finally, we comment on implications of these results to the axion search experiments, including microwave cavity and the Orpheus experiments.

Minimal nonsupersymmetricSO(10)model: Gauge coupling unification, proton decay, and fermion masses

We present a minimal renormalizable non-supersymmetric SO(10) grand unified model with a symmetry breaking sector consisting of Higgs fields in the 54_H + 126_H + 10_H representations. This model admits a single intermediate scale associated with Pati-Salam symmetry along with a discrete parity. Spontaneous symmetry breaking, the unification of gauge couplings and proton lifetime estimates are studied in detail in this framework. Including threshold corrections self-consistently, obtained from a full analysis of the Higgs potential, we show that the model is compatible with the current experimental bound on proton lifetime. The model generally predicts an upper bound of few times 10^{35} yrs for proton lifetime, which is not too far from the present Super-Kamiokande limit of \tau_p \gtrsim 1.29 \times 10^{34} yrs. With the help of a Pecci-Quinn symmetry and the resulting axion, the model provides a suitable dark matter candidate while also solving the strong CP problem. The intermediate scale, M_I \approx (10^{13}-10^{14}) GeV which is also the B-L scale, is of the right order for the right-handed neutrino mass which enables a successful description of light neutrino masses and oscillations. The Yukawa sector of the model consists of only two matrices in family space and leads to a predictive scenario for quark and lepton masses and mixings. The branching ratios for proton decay are calculable with the leading modes being p \rightarrow e^+ \pi^0 and p \rightarrow \overline{\nu} \pi^+. Even though the model predicts no new physics within the reach of LHC, the next generation proton decay detectors and axion search experiments have the capability to pass verdict on this minimal scenario.

Calculation of axion–photon–photon coupling in string theory

The axion search experiments invite a plausible estimation of the axion–photon–photon coupling constant c¯aγγ in string models with phenomenologically acceptable visible sectors. We present the calculation of c¯aγγ with an exact Peccei–Quinn symmetry. In the Huh–Kim–Kyae Z12−I orbifold compactification, we obtain c¯aγγ=1123388, and the low-temperature axion search experiments will probe the QCD corrected coupling, caγγ≃c¯aγγ−1.98≃0.91.

MICROMEGAS IN THE RARE EVENT SEARCHES FIELD

The Micromegas detectors have been gaining importance as reliable options in their implementation to Time Projection Chambers (TPCs) in experiments searching for Rare Events mainly due to their demonstrated good performance regarding low background levels, energy and time resolution, gain and stability of operation. In the present paper, we will briefly review the latest developments carried out within the T-REX project of detector R&D, and the performance achieved in the context of several experiments: the CAST solar axion search experiment, the NEXT experiment of double beta decay and the MIMAC dark matter directional search.

Generation and search of axion-like light particle using intense crystalline field

Intense electric field ∼1010–1011 V/cm in crystal has been known for a long time and has wide applications. We study the conversion of axion-like light particle and photon in the intense electric field in crystal. We find that the conversion of axion-like particle and photon happens for energy larger than keV range. We propose search of axion-like light particle using the intense crystalline field. We discuss the solar axion search experiment and a variety of shining-through-wall experiment using crystalline field. Due to the intense crystalline field which corresponds to magnetic field ∼104–105 Tesla these experiments are very interesting. In particular these experiments can probe the mass range of axion-like particle from eV to keV.

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.

Performance of the micromegas detector in the CAST experiment

The gaseous micromegas detector designed for the CERN Axion search experiment CAST, operated smoothly during Phase-I, which included the 2003 and 2004 running periods. It exhibited linear response in the energy range of interest (1–10 keV), good spatial sensitivity and energy resolution (15–19% FWHM at 5.9 keV) as well as remarkable stability. The detector's upgrade for the 2004 run, supported by the development of advanced offline analysis tools, improved the background rejection capability, leading to an average rate 5×10 −5 counts/s/cm 2/keV with 94% cut efficiency. Also, the origin of the detected background was studied with a Monte-Carlo simulation, using the GEANT4 package.

A Low Background Micromegas Detector for Axion Searches

A micropattern low-background detector based on the Micromegas technology has been designed and constructed for the CERN Axion Search experiment CAST. The detector is made of low natural radioactivity materials and has a two-dimensional readout with X–Y strip structure. It is operated with an Argon/Isobutane (95%/5%) mixture and is controlled by a VME data acquisition system. The detector is sensitive to photons in the energy range of 1–10 keV, it has a linear response, excellent stability and a very good energy resolution (14% FWHM at 5.9 keV). This device has been in stable operation since October 2002, taking data during the running periods of the CAST experiment. At the end of summer 2003, the detector was upgraded with a flash ADC readout of the grid signal to further improve its background rejection capability. The currently achieved background rate under normal operation is about 2.0 � 10 � 5 events/keV/cm 2 /s with better than 85% software efficiency.

Building a 3.5 m prototype interferometer for the Q&A vacuum birefringence experiment and high-precision ellipsometry

We have built and tested a 3.5 m high-finesse Fabry–Perot prototype interferometer with a precision ellipsometer for the QED test and axion search (Q&A) experiment. We use X-pendulum–double-pendulum suspension designs and automatic control schemes developed by the gravitational-wave detection community. The Verdet constant and Cotton–Mouton constant of the air are measured as a test. Double modulation with polarization modulation 100 Hz and magnetic-field modulation 0.05 Hz gives 10−7 rad phase noise for a 44 min integration.

The Tokyo axion helioscope experiment

A preliminary result of the solar axion search experiment at the University of Tokyo is presented. We searched for axions which could be produced in the solar core by exploiting the axion helioscope. The helioscope consists of a superconducting magnet with field strength of 4 Tesla over 2.3 meters. From the absence of the axion signal we set a 95% confidence level upper limit on the axion coupling to two photons g aγγ < 6.0 × 10 −10GeV −1 for the axion mass m a <0.03 eV. This is the first solar axion search experiment whose sensitivity to g aγγ exceeds the limit inferred from the solar age consideration.

Axion potential, topological defects and CP-odd bubbles in QCD

It follows on general grounds that the θ dependence in QCD is more complicated than suggested by the large N c approach or instanton arguments. Generically, the vacuum energy E vac ( θ) is a multi-valued function of θ admitting the existence of metastable states. We discuss decays of such metastable vacua in the theory with and without the axion, and point out the potential relevance of this and related phenomena for constraining a dark matter axion. Based on the analysis of the axion potential, an idea for a new axion search experiment at RHIC is suggested. It is noted that the false vacuum decay proceeds with maximal violation of CP, even if θ=0. We further speculate that the famous Sakharov criteria for baryogenesis could be satisfied at the QCD scale.

Are Isocurvature Fluctuations of the M-Theory Axion Observable?

Banks and Dine have recently shown that the M theory naturally accommodates the Peccei-Quinn axion. Since the decay constant $F_a$ of the axion is large as $F_a \simeq 10^{15}-10^{16}$GeV, the halo axion is hardly detected in coming axion-search experiments. However, we show that isocurvature fluctuations of the M-theory axion produced at the inflationary epoch are most likely detectable in future satellite experiments on anisotropies of the cosmic microwave background radiation.

Do axions need inflation?

Without inflation the energy density of relic axions in a Robertson-Walker universe arises not from coherent oscillations of a zero-momentum mode but from radiative decay of axion strings. An estimate of the upper bound on the PQ scale coming from these axions is in conflict with the lower bound from SN1987a. We present analytical and numerical evidence supporting this estimate. If true, then the axion needs inflation. With inflation the axion is safe, but the motivation for axion search experiments is weakened.