Search

The axion haloscope is the currently most sensitive method to probe the vanishingly small coupling of this prominent Dark Matter candidate to photons. To scan a sizeable axion Dark Matter parameter space, the cavities that make up the haloscope need to be tuned efficiently. In this article, we describe a novel technique to tune axion haloscopes around 8.4 GHz in a purely mechanical manner without the use of dielectrics. We achieve tuning by introducing a gap along the cavity geometry. A quality factor reduction of less than 20% is achieved experimentally for a tuning range of around 600 MHz at room temperature and at cryogenic temperatures for around 300 MHz. A larger tuning range would require an improved alignments mechanism. We present the results of a corresponding prototype and outline prospects to further develop this technique. [ABSTRACT FROM AUTHOR]

A collaboration between CNRS-Grenoble and IBS-CAPP Daejeon plans to build a Sikivie's type haloscope for axion/ALPs dark matter search at the Dine-Fischler-Srednicki-Zhitnitskii sensitivity for the 300--600 MHz range. It will be based on the large-bore superconducting "outsert" coil of the Grenoble hybrid magnet, providing a central magnetic field up to 9 T in an 810-mm warm bore diameter. This magnet has recently been successfully powered up to 8.5 T, achieving the first step of the electrical commissioning phase. The design principles of the cryostat with its double dilution refrigerators to cool below 50 mK, the light Cu RF cavity of 700-mm diameter, and its tuning rod(s) and the first stages of the measurement chain are presented. Perspectives for the targeted sensitivity assuming less than a 2-year integration time are given. [ABSTRACT FROM AUTHOR]

The axion offers a well-motivated solution to two fundamental questions in modern physics: the strong CP problem and the dark matter mystery. Cavity haloscopes, exploiting resonant enhancement of photon signals, provide the most sensitive searches for axion dark matter in the microwave region. However, current experimental sensitivities are limited to the O(100) µeV range, while recent theoretical predictions for the axion mass favor up to O(10²) µeV, suggesting the need of new experimental approaches that are suitable for higher mass regions. CAPP has developed/proposed several haloscopes effective for high-mass axion searches based on new cavity concepts and practical tuning mechanisms. They are characterized by large detection volumes and/or high quality factors at high frequencies, achieved by partitioning a single cavity into multiple cells, exploiting higher-order resonant modes, and constructing dielectric photonic crystal structures. Improving on the dish antenna haloscope scheme, a horn antenna array has also been proposed for volume-efficient broadband search in the THz region. We review these haloscope designs for sensitive search in the high-mass regions and discuss their impacts on future experiments. [ABSTRACT FROM AUTHOR]

There is an ongoing debate on how seriously one should take the naturalness puzzles as the guidelines to new physics. In this debate gravity is often put aside, as an insignificant spectator force. However, this attitude misses the entire essence of the story. Through its S -matrix formulation, gravity promotes certain puzzles, such as the cosmological constant and strong- CP problems, into the consistency issues. The respective consistency requirements make the theory highly predictive. In particular, the cosmological vacuum energy must be zero. This has fundamental implications both for strong- CP and for dark energy puzzles. QCD must include an axion as an intrinsic part of the gauge redundancy, without the need of any global symmetry. This gives ϑ¯=0 to all orders in operator expansion. Applied to cosmology, the S -matrix implies that the energy budget of the Universe cannot come from a constant. Correspondingly, the dark energy is an unambiguous signal of new physics around the Hubble scale. This article is part of the theme issue 'The particle-gravity frontier'. [ABSTRACT FROM AUTHOR]

Within the framework of the extended Einstein–aether–axion theory, we studied the model of a two-level aetheric control over the evolution of a spatially isotropic homogeneous Universe filled with axionic dark matter. Two guiding functions are introduced, which depend on the expansion scalar of the aether flow being equal to the tripled Hubble function. The guiding function of the first type enters the aetheric effective metric, which modifies the kinetic term of the axionic system; the guiding function of the second type predetermines the structure of the potential axion field. We obtained new exact solutions to the total set of master equations in the model (with and without cosmological constant), and studied four analytically solvable submodels in detail, for which both guiding functions are reconstructed and illustrations of their behavior are presented. [ABSTRACT FROM AUTHOR]

The axion is a long-postulated boson that can simultaneously solve two fundamental problems of modern physics: the charge–parity symmetry problem in the strong interaction and the enigma of dark matter. In this work, we estimate, by means of Monte Carlo simulations, the sensitivity of the Dark-photons & Axion-Like particles Interferometer (DALI), a new-generation Fabry–Pérot haloscope proposed to probe axion dark matter in the 25–250 μ eV band. [ABSTRACT FROM AUTHOR]

The axion or axion-like particle motivated from a natural solution of strong CP problem or string theory is a promising dark matter candidate. We study the new observational effects of ultralight axion-like particles by the space-borne gravitational wave detector and the radio telescope. Taking the neutron star-black hole binary as an example, we demonstrate that the gravitational waveform could be obviously modified by the slow depletion of the axion cloud around the black hole formed through the superradiance process. We compare these new effects on the binary with the well-studied effects from dynamical friction with dark matter and dipole radiation in model-independent ways. Finally, we discuss the constraints from LIGO/Virgo and study the detectability of the ultralight axion particles at LISA and TianQin. [ABSTRACT FROM AUTHOR]

The axion haloscope is the currently most sensitive method to probe the vanishingly small coupling of this prominent Dark Matter candidate to photons. To scan a sizeable axion Dark Matter parameter space, the cavities that make up the haloscope need to be tuned efficiently. In this article, we describe a novel technique to tune axion haloscopes around 8.4 GHz in a purely mechanical manner without the use of dielectrics. We achieve tuning by introducing a gap along the cavity geometry. A quality factor reduction of less than 20% is achieved experimentally for a tuning range of around 600 MHz at room temperature and at cryogenic temperatures for around 300 MHz. A larger tuning range would require an improved alignments mechanism. We present the results of a corresponding prototype and outline prospects to further develop this technique.

A collaboration between CNRS-Grenoble and IBS-CAPP Daejeon plans to build a Sikivie’s type haloscope for axion/ALPs dark matter search at the Dine-Fischler-Srednicki-Zhitnitskii sensitivity for the 300–600 MHz range. It will be based on the large-bore superconducting “outsert” coil of the Grenoble hybrid magnet, providing a central magnetic field up to 9 T in an 810-mm warm bore diameter. This magnet has recently been successfully powered up to 8.5 T, achieving the first step of the electrical commissioning phase. The design principles of the cryostat with its double dilution refrigerators to cool below 50 mK, the light Cu RF cavity of 700-mm diameter, and its tuning rod(s) and the first stages of the measurement chain are presented. Perspectives for the targeted sensitivity assuming less than a 2-year integration time are given.

Axion Dark Matter (DM) is studied on the formation of SuperMassive Black Holes (SMBH) at high red shift z. It is shown that the attractive self-interaction of this DM may resolve the tension between the large mass with high angular momentum of SMBH and its early time formation. We consider the ultra-light axion DM around O (1 0 − 2 1) eV as its origin, which may also cause nano-Hz stochastic gravitational wave background recently observed. [ABSTRACT FROM AUTHOR]

The dynamics of spin in external electromagnetic, gravitational, and axion fields is analyzed in the framework of the gravitoelectromagnetism approach in Einstein's general relativity theory. We consistently extend the recent studies from the flat Minkowski geometry to the curved spacetime manifolds, contributing to the discussion of the possible new role of a precessing spin as an "axion antenna" that can be used to detect the hypothetical axion-like dark matter. The formalism developed helps to clarify the subtle influence of the gravitational/inertial and axion fields in the ultra-sensitive high-energy spin experiments with charged particles and neutrons at accelerators and storage rings devoted to testing fundamental physical symmetries, including attempts to establish the nature of dark matter in the Universe. [ABSTRACT FROM AUTHOR]

We use the Trans-Planckian Censorship Conjecture (TCC) to constrain the decay constants f characterizing a set of N identical axion-like fields with cosine potentials, improving upon the precision of other Swampland conjectures and existing string-theoretic arguments. We find that consistency with the TCC requires any such set of axion-like fields to satisfy fN≲0.6Mpl, where Mpl is the reduced Planck mass. We show that this bound makes models of axion-driven inflation incapable of simultaneously producing the required number of e-foldings and the observed scalar spectral tilt. In contrast, we find that models of axion quintessence can be simultaneously compatible with the TCC and observational data, provided that the axions' initial field values are set near the maxima of their potentials to within roughly ±π5f.

The direct effect of an axion field on Josephson junctions is analyzed through the consequences on the effective potential barrier that prevents the junction from switching from the superconducting to the finite-voltage state. We describe a method to reliably compute the quasipotential with stochastic simulations, which allows for the spanning of the coupling parameter from weakly interacting axion to tight interactions. As a result, we obtain an axion field that induces a change in the potential barrier, therefore determining a significant detectable effect for such a kind of elusive particle. [ABSTRACT FROM AUTHOR]

We aim to search for axion-like particles in the eV mass range using a variable-angle stimulated resonance photon collider (SRPC) with three intense laser beams. By changing angle of incidence of the three beams, the center-of-mass-system collision energy can be varied and the eV mass range can be continuously searched for. In this paper, we present the design and construction of such a variable-angle three-beam SRPC ( t SRPC ), the verification of the variable-angle mechanism using a calibration laser, and realistic sensitivity projections for searches in the near future. [ABSTRACT FROM AUTHOR]

We investigate the mass range and the corresponding free-streaming length scale of dark matter produced non-thermally from decay of heavy objects which can be either dominant or sub-dominant at the moment of decay. We show that the resulting dark matter could be very light well below keV scale with a free-streaming length satisfying the Lyman-α constraints. We demonstrate two explicit examples for such light cold dark matter.

Within the framework of the extended Einstein–aether–axion theory, we studied the model of a two-level aetheric control over the evolution of a spatially isotropic homogeneous Universe filled with axionic dark matter. Two guiding functions are introduced, which depend on the expansion scalar of the aether flow being equal to the tripled Hubble function. The guiding function of the first type enters the aetheric effective metric, which modifies the kinetic term of the axionic system; the guiding function of the second type predetermines the structure of the potential axion field. We obtained new exact solutions to the total set of master equations in the model (with and without cosmological constant), and studied four analytically solvable submodels in detail, for which both guiding functions are reconstructed and illustrations of their behavior are presented.

The axion is a long-postulated boson that can simultaneously solve two fundamental problems of modern physics: the charge–parity symmetry problem in the strong interaction and the enigma of dark matter. In this work, we estimate, by means of Monte Carlo simulations, the sensitivity of the Dark-photons & Axion-Like particles Interferometer (DALI), a new-generation Fabry–Pérot haloscope proposed to probe axion dark matter in the 25–250 μeV band.

Axion‐like particles (ALPs) and heavy neutral leptons (HNLs) are both well‐motivated extensions of the Standard Model. As ALPs couple to on‐shell fermions proportionally to their masses, processes involving both types of particles may give rise, for TeV HNLs, to relevant phenomenology at colliders. In this work, we point out a particularly clean process, whose final state consists of four jets and two charged leptons, and we estimate its current and future sensitivity at the LHC. For on‐shell HNLs, i) there is no dependence on the overall scale of the mixing between HNLs and the active neutrinos, making this process sensitive down to the type‐I Seesaw line; ii) the signal strength of the process is sizable only as far as the HNL masses are below a few TeVs, contrary to what the proportionality to masses of the ALP couplings may suggest. Although ALPs and HNLs have been mainly studied independently in the literature, considering their interplay may lead to joint limits that are much stronger than those on the individual particles taken separately. This concise study paves the way for similar searches at colliders and other experiments. [ABSTRACT FROM AUTHOR]

Ultralight axions and dark photons are well-motivated dark matter candidates. Inside the plasma, once the mass of ultralight dark matter candidates equals the plasma frequency, they can resonantly convert into electromagnetic waves, due to the coupling between the ultralight dark matter particles and the standard model photons. The converted electromagnetic waves are monochromatic. In this article, we review the development of using radio detectors to search for ultralight dark matter conversions in the solar corona and solar wind plasma. [ABSTRACT FROM AUTHOR]

Toward the systematic search for axion-like particles in the eV mass range, we proposed the concept of a stimulated resonant photon collider by focusing three short pulse lasers into a vacuum. In order to realize such a collider, we have performed a proof-of-principle experiment with a set of large incident angles between three beams to overcome the expected difficulty to ensure the space–time overlap between short pulse lasers and also established a method to evaluate the bias on the polarization states, which is useful for a future variable–incident–angle collision system. In this paper, we present a result from the pilot search with the developed system and the method. The search result was consistent with null. We thus have set the upper limit on the minimum ALP-photon coupling down to 1.5 × 10 − 4 GeV − 1 at the ALP mass of 1.53 eV with a confidence level of 95%. [ABSTRACT FROM AUTHOR]

It has recently been observed that solar spicules covering almost all of solar surface have strong magnetic field B ∼ 1 0 2 G. They are supposed to be plasma jets emitted from chromosphere and they arrive up to ∼ 1 0 4 km. Their electron number density is such that n e = 1 0 1 0 cm − 3 ∼ 1 0 1 2 cm − 3 . Corresponding plasma frequency m p = e 2 n e / m e (electron mass m e ) is nearly equal to axion mass m a = 1 0 − 5 eV ∼ 1 0 − 4 eV. Thus, resonant radiation conversion of axion with the mass can arise in the spicules. We show that radiations converted from axion dark matter possess flux density ∼ 1 0 − 6 Jy (m a / 1 0 − 4 eV) (B / 3 × 1 0 2 G) 2 . The radiations show line spectrum with frequency ≃ 2 4 GHz (m a / 1 0 − 4 eV). Our estimation has fewer ambiguities in physical parameters than similar estimation in neutron stars because physical parameters like electron number density have been more unambiguously observed in the sun. But, much strong solar thermal radiations would preclude sensitive observations of such radiations from the axions. [ABSTRACT FROM AUTHOR]

We propose a three-beam stimulated resonant photon collider with focused laser fields in order to directly produce an axion-like particle (ALP) with the two beams and to stimulate its decay by the remaining one. The expected sensitivity around the eV mass range has been evaluated. The result shows that the sensitivity can reach the ALP-photon coupling down to O (10 − 14) GeV−1 with 1 J class short-pulsed lasers. [ABSTRACT FROM AUTHOR]

Dark matter in the form of axions is expected to form axion stars. Such axion stars could be discovered by microlensing events. In particular, some candidate events reported by Subaru HSC and OGLE can be explained simultaneously if the axion stars with masses of the order of the Earth mass make up about ∼27−13+7 percent of dark matter. For QCD axions, this corresponds to the axion mass in the range 10−9−10−6 eV, which is consistent with the experimental constraints, as well as the cosmological anthropic window of parameters.

The standard flavour-blind DFSZ axion model for solving the strong-CP problem has in the past been extended to account for nonzero neutrino masses and baryogenesis-via-leptogenesis through the Type-I seesaw mechanism, in addition to having viable axion dark matter. Constructing a full and viable cosmological history, however, requires dealing with the cosmological domain wall problem posed by standard DFSZ. In this paper, I report on work with A. Sopov where this challenge is addressed through a flavourvariant model called VISHν that removes the domain wall problem and incorporates successful Higgs- Peccei-Quinn scalar inflation. As part of this, we ensure that the required new high-scale physics does not add to the electroweak naturalness problem.

An interpretation is proposed for the spectral broadening and the change in angular characteristics of the light beam at the exit from a dispersion medium. The role of axions responsible for changes in the spectral and angular characteristics of the light beam is examined. [ABSTRACT FROM AUTHOR]

The axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the Peccei–Quinn (PQ) symmetry, could have originated with initial non-zero velocity. The presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the PQ symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional PQ framework or an explanation for the observed matter-antimatter asymmetry. We elaborate further on the consequences of the "kinetic misalignment" mechanism, assuming that axions form the entirety of the dark matter abundance. The kinetic misalignment mechanism possesses a weak limit in which the axion field starts to oscillate at the same temperature as in the conventional PQ framework, and a strong limit corresponding to large initial velocities which effectively delay the onset of oscillations. Following a UV-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures. [ABSTRACT FROM AUTHOR]

Particle production during cosmic expansion can be interpreted as a two-mode squeezing process of quantum states. The two-mode squeezed states consist of an infinite number of entangled particles and then enhance the nonclassicality of particles. There are two methods for estimating the degree of squeezing. One is to employ instantaneous vacuum states, and the other is to adopt adiabatic vacuum states. We analytically study the squeezing process of gravitons and axions by using the two methods. We first consider a cosmological model of inflation followed by instantaneous reheating leading to a radiation dominated era. In the case of gravitons, we find no qualitatively difference in the squeezing between the two methods. However, for the axions, it turns out that the squeezing in the instantaneous vacuum increases as the mass increases while the squeezing decreases in the adiabatic vacuum as the mass increases. We then study the effect of noninstantaneous reheating on the the squeezing and show that the squeezing is enhanced compared with the instantaneous reheating. We also illustrate how the squeezed states enhance the violation of Bell inequality and quantum noise of gravitons and axions. [ABSTRACT FROM AUTHOR]

The direct effect of an axion field on Josephson junctions is analyzed through the consequences on the effective potential barrier that prevents the junction from switching from the superconducting to the finite-voltage state. We describe a method to reliably compute the quasipotential with stochastic simulations, which allows for the spanning of the coupling parameter from weakly interacting axion to tight interactions. As a result, we obtain an axion field that induces a change in the potential barrier, therefore determining a significant detectable effect for such a kind of elusive particle.

We aim to search for axion-like particles in the eV mass range using a variable-angle stimulated resonance photon collider (SRPC) with three intense laser beams. By changing angle of incidence of the three beams, the center-of-mass-system collision energy can be varied and the eV mass range can be continuously searched for. In this paper, we present the design and construction of such a variable-angle three-beam SRPC (tSRPC), the verification of the variable-angle mechanism using a calibration laser, and realistic sensitivity projections for searches in the near future.

We establish a nonlinear version of the SU(N)-symmetric theory, which describes self-consistently the interaction between the gravitational, gauge, vector and pseudoscalar (axion) fields. In the context of this theory the SU(N)-symmetric multiplet of vector fields is associated with the color aether, the decay of which in the early Universe produced the canonic dynamic aether and the axionic dark matter. The SU(N)-symmetric Yang–Mills field, associated with the color aether, forms the source, which transfers the energy of the decaying color aether to the axion field. The nonlinear modification of the model uses explicitly the requirement of discrete symmetry, prescribed by the axion field, and is based on the analogy with a nonlinear physical pendulum. We show that in the framework of this nonlinear regular model, the axion field can grow to an arbitrarily large value, thus explaining the abundance of the axionic dark matter in the Universe. [ABSTRACT FROM AUTHOR]

The concept of detecting gravitational waves using RF-cavities in strong magnetic fields has gained considerable interest, using setups currently running axion searches. We propose a novel analysis approach for detecting GHz-regime gravitational waves, potentially from primordial black hole mergers, through synchronous measurements from multiple, distant cavities. While individual cavities may detect gravitational wave signatures, isolating them from noise is challenging since the strain (and thereby power deposition in a cavity) of such mergers is expected to be very small and short-lived. By correlating signals from several geographically separated cavities, we can significantly improve the signal-to-noise ratio and potentially investigate the sources of these waves. A demonstration experiment with a superconducting cavity is currently underway, forming the basis for our data analysis methods and outlining the prospects for the GravNet project. This project should be seen as an effort to bring the axion community together and collaborate in the context of gravitational wave physics. [ABSTRACT FROM AUTHOR]