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88-411: The axion is a hypothetical elementary particle originally postulated to solve the strong CP problem . The axion is also an extremely attractive dark matter candidate. The axion is the puzzle piece allowing these two mysteries to fit naturally into our understanding of the universe. The axion was originally postulated to exist as part of the solution to the "strong CP problem". This problem arose from

176-470: A Weyl semimetal material. In the axion insulator phase, the material has an axion-like quasiparticle – an excitation of electrons that behave together as an axion – and its discovery demonstrates the consistency of axion electrodynamics as a description of the interaction of axion-like particles with electromagnetic fields. In this way, the discovery of axion-like quasiparticles in axion insulators provides motivation to use axion electrodynamics to search for

264-454: A 225-day run to set the best coupling limits to date and exclude some parameters. While Schiff's theorem states that a static nuclear electric dipole moment (EDM) does not produce atomic and molecular EDMs, the axion induces an oscillating nuclear EDM that oscillates at the Larmor frequency . If this nuclear EDM oscillation frequency is in resonance with an external electric field, a precession in

352-722: A HEMT device, the D-HEMT, was presented by Mimura and Satoshi Hiyamizu in May 1980, and then they later demonstrated the first E-HEMT in August 1980. Independently, Daniel Delagebeaudeuf and Tranc Linh Nuyen, while working at Thomson-CSF in France, filed a patent for a similar type of field-effect transistor in March 1979. It also cites the Bell Labs patent as an influence. The first demonstration of an "inverted" HEMT

440-461: A junction at equilibrium similar to a p–n junction . Note that the undoped narrow band gap material now has excess majority charge carriers. The fact that the charge carriers are majority carriers yields high switching speeds, and the fact that the low band gap semiconductor is undoped means that there are no donor atoms to cause scattering and thus yields high mobility. In the case of GaAs HEMTs, they make use of high mobility electrons generated using

528-665: A junction between two materials with different band gaps (i.e. a heterojunction ) as the channel instead of a doped region (as is generally the case for a MOSFET ). A commonly used material combination is GaAs with AlGaAs , though there is wide variation, dependent on the application of the device. Devices incorporating more indium generally show better high-frequency performance, while in recent years, gallium nitride HEMTs have attracted attention due to their high-power performance. Like other FETs , HEMTs can be used in integrated circuits as digital on-off switches. FETs can also be used as amplifiers for large amounts of current using

616-448: A large electric dipole moment (EDM) for the neutron . Experimental constraints on the unobserved EDM implies CP violation from QCD must be extremely tiny and thus Θ must itself be extremely small. Since Θ could have any value between 0 and 2 π , this presents a "naturalness" problem for the standard model. Why should this parameter find itself so close to zero? (Or, why should QCD find itself CP-preserving?) This question constitutes what

704-462: A magnetic field. The concept was first put forward in 1986 by Luciano Maiani , Roberto Petronzio and Emilio Zavattini . A rotation claim in 2006 was excluded by an upgraded setup. An optimized search began in 2014. Another technique is so called "light shining through walls", where light passes through an intense magnetic field to convert photons into axions, which then pass through metal and are reconstituted as photons by another magnetic field on

792-436: A new particle called the axion . If the axion is very light, it interacts so weakly that it would be nearly impossible to detect but would be an ideal dark matter candidate. The ADMX experiment aims to detect this extraordinarily weakly coupled particle. Although dark matter can't be seen directly, its gravitational interactions with familiar matter leave unmistakable evidence for its existence. The universe today would not look

880-411: A possible origin for both phenomena. In 2022 a similar hypothesis was used to constrain the mass of the axion from data of M87*. In 2020, it was proposed that the axion field might actually have influenced the evolution of the early Universe by creating more imbalance between the amounts of matter and antimatter – which possibly resolves the baryon asymmetry problem. In supersymmetric theories

968-448: A set of equations that imposed duality symmetry, assuming the existence of magnetic monopoles . However, these alternative formulations are less theoretically motivated, and in many cases cannot even be derived from an action . A term analogous to the one that would be added to Maxwell's equations to account for axions also appears in recent (2008) theoretical models for topological insulators giving an effective axion description of

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1056-517: A small voltage as a control signal. Both of these uses are made possible by the FET’s unique current–voltage characteristics . HEMT transistors are able to operate at higher frequencies than ordinary transistors, up to millimeter wave frequencies, and are used in high-frequency products such as cell phones , satellite television receivers, voltage converters , and radar equipment. They are widely used in satellite receivers, in low power amplifiers and in

1144-469: A solution to the apparent transparency of the Universe to TeV photons. It has also been demonstrated that, in the large magnetic fields threading the atmospheres of compact astrophysical objects (e.g., magnetars ), photons will convert much more efficiently. This would in turn give rise to distinct absorption-like features in the spectra detectable by early 21st century telescopes. A new (2009) promising means

1232-485: A strained SiGe layer. In the strained layer, the germanium content increases linearly to around 40-50%. This concentration of germanium allows the formation of a quantum well structure with a high conduction band offset and a high density of very mobile charge carriers . The end result is a FET with ultra-high switching speeds and low noise. InGaAs / AlGaAs , AlGaN / InGaN , and other compounds are also used in place of SiGe. InP and GaN are starting to replace SiGe as

1320-438: A theoretical team from Massachusetts Institute of Technology devised a possible way of detecting axions using a strong magnetic field that need be no stronger than that produced in an MRI scanning machine. It would show variation, a slight wavering, that is linked to the mass of the axion. Results from the ensuing experiment published in 2021 reported no evidence of axions in the mass range from 4.1x10 to 8.27x10 eV. In 2022

1408-428: A yoctowatt) into the cavity. An extraordinarily sensitive microwave receiver allows the weak axion signal to be extracted from the noise. The experiment receiver features quantum-limited noise performance delivered by a Superconducting QUantum Interference Device (SQUID) amplifier and lower temperatures from a He refrigerator. ADMX is the first experiment sensitive to realistic dark-matter axion masses and couplings and

1496-511: Is a hypothetical elementary particle originally theorized in 1978 independently by Frank Wilczek and Steven Weinberg as the Goldstone boson of Peccei–Quinn theory , which had been proposed in 1977 to solve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter . As shown by Gerard 't Hooft , strong interactions of

1584-606: Is a kind of scalar field dark matter that seems to solve the small scale problems of CDM. A single ULA with a GUT scale decay constant provides the correct relic density without fine-tuning. Axions would also have stopped interaction with normal matter at a different moment after the Big Bang than other more massive dark particles. The lingering effects of this difference could perhaps be calculated and observed astronomically. If axions have low mass, thus preventing other decay modes (since there are no lighter particles to decay into),

1672-412: Is a secondary ADMX experiment demonstrating the use of dielectrically loaded Fabry–Pérot cavity to search for higher mass axions and dark photons near 70 μeV. In 2022, Orpheus reported results of a first search between 65.5 μeV (15.8 GHz) and 69.3 μeV (16.8 GHz). With hardware upgrades, Orpheus is projected to perform searches from 45 to 80 μeV. Axion An axion ( / ˈ æ k s i ɒ n / )

1760-517: Is known as the strong CP problem . In 1977, Roberto Peccei and Helen Quinn postulated a more elegant solution to the strong CP problem, the Peccei–Quinn mechanism . The idea is to effectively promote Θ to a field. This is accomplished by adding a new global symmetry (called a Peccei–Quinn (PQ) symmetry ) that becomes spontaneously broken. This results in a new particle, as shown independently by Frank Wilczek and Steven Weinberg , that fills

1848-401: Is looking for quasi-particle refraction in systems with strong magnetic gradients. In particular, the refraction will lead to beam splitting in the radio light curves of highly magnetized pulsars and allow much greater sensitivities than currently achievable. The International Axion Observatory (IAXO) is a proposed fourth generation helioscope . Axions can resonantly convert into photons in

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1936-432: Is positive, causing the 2D electron gas to be formed even if there is no doping. Such a transistor is normally on, and will turn off only if the gate is negatively biased - thus this kind of HEMT is known as depletion HEMT , or dHEMT . By sufficient doping of the barrier with acceptors (e.g. Mg ), the built-in charge can be compensated to restore the more customary eHEMT operation, however high-density p-doping of nitrides

2024-432: Is so small that the entire experiment is cooled to well below 4.2 kelvin with a liquid helium refrigerator to minimize thermal noise. The electric field within the cavity is sampled by a tiny antenna connected to an ultra-low-noise microwave receiver. The ultra-low noise microwave receiver makes the experiment possible. The dominant background is thermal noise arising from the cavity and the receiver electronics. Signals from

2112-532: Is technologically challenging due to dopant diffusion into the channel. In contrast to a modulation-doped HEMT, an induced high electron mobility transistor provides the flexibility to tune different electron densities with a top gate, since the charge carriers are "induced" to the 2DEG plane rather than created by dopants. The absence of a doped layer enhances the electron mobility significantly when compared to their modulation-doped counterparts. This level of cleanliness provides opportunities to perform research into

2200-814: Is to place a buffer layer between them. This is done in the mHEMT or metamorphic HEMT, an advancement of the pHEMT. The buffer layer is made of AlInAs , with the indium concentration graded so that it can match the lattice constant of both the GaAs substrate and the GaInAs channel. This brings the advantage that practically any Indium concentration in the channel can be realized, so the devices can be optimized for different applications (low indium concentration provides low noise ; high indium concentration gives high gain ). HEMTs made of semiconductor hetero-interfaces lacking interfacial net polarization charge, such as AlGaAs/GaAs, require positive gate voltage or appropriate donor-doping in

2288-417: Is violated is called a pHEMT or pseudomorphic HEMT. This is achieved by using an extremely thin layer of one of the materials – so thin that the crystal lattice simply stretches to fit the other material. This technique allows the construction of transistors with larger bandgap differences than otherwise possible, giving them better performance. Another way to use materials of different lattice constants

2376-805: The CERN Axion Solar Telescope converts axions produced in the Sun's core to X-rays, and other experiments search for axions produced in laser light. As of the early 2020s, there are dozens of proposed or ongoing experiments searching for axion dark matter. The equations of axion electrodynamics are typically written in "natural units", where the reduced Planck constant ℏ {\displaystyle \hbar } , speed of light c {\displaystyle c} , and permittivity of free space ε 0 {\displaystyle \varepsilon _{0}} all reduce to 1 when expressed in these "natural units". In this unit system,

2464-575: The Peccei-Quinn mechanism for solving the strong CP problem required such large couplings. However, it was soon realized that "invisible axions" with much smaller couplings also work. Two such classes of models are known in the literature as KSVZ ( Kim – Shifman – Vainshtein – Zakharov ) and DFSZ ( Dine – Fischler – Srednicki – Zhitnitsky ). The very weakly coupled axion is also very light, because axion couplings and mass are proportional. Satisfaction with "invisible axions" changed when it

2552-517: The Primakoff effect , which converts axions to photons and vice versa in electromagnetic fields. The Axion Dark Matter Experiment (ADMX) at the University of Washington uses a strong magnetic field to detect the possible weak conversion of axions to microwaves . ADMX searches the galactic dark matter halo for axions resonant with a cold microwave cavity. ADMX has excluded optimistic axion models in

2640-615: The XENON1T experiment at the Gran Sasso National Laboratory in Italy reported a result suggesting the discovery of solar axions. The results were not significant at the 5-sigma level required for confirmation, and other explanations of the data were possible though less likely. New observations made in July 2022 after the observatory upgrade to XENONnT discarded the excess, thus ending

2728-503: The bipolar junction transistor and the MOSFET , are the higher operating temperatures, higher breakdown strengths , and lower specific on-state resistances, all in the case of GaN-based HEMTs compared to Si-based MOSFETs. Furthermore, InP-based HEMTs exhibit low noise performance and higher switching speeds. The wide band element is doped with donor atoms; thus it has excess electrons in its conduction band. These electrons will diffuse to

Axion Dark Matter Experiment - Misplaced Pages Continue

2816-514: The light-by-light scattering process. Those searches are sensitive for rather large axion masses between 100 MeV/c and hundreds of GeV/c . Assuming a coupling of axions to the Higgs boson, searches for anomalous Higgs boson decays into two axions can theoretically provide even stronger limits. It was reported in 2014 that evidence for axions may have been detected as a seasonal variation in observed X-ray emission that would be expected from conversion in

2904-629: The magnetospheres of neutron stars . The emerging photons lie in the GHz frequency range and can be potentially picked up in radio detectors, leading to a sensitive probe of the axion parameter space. This strategy has been used to constrain the axion–photon coupling in the 5–11 μeV mass range, by re-analyzing existing data from the Green Bank Telescope and the Effelsberg 100 m Radio Telescope . A novel, alternative strategy consists in detecting

2992-504: The wurtzite one, which has built-in electrical polarisation. Since this polarization differs between the GaN channel layer and AlGaN barrier layer, a sheet of uncompensated charge in the order of 0.01-0.03 C/m 2 {\displaystyle ^{2}} is formed. Due to the crystal orientation typically used for epitaxial growth ("gallium-faced") and the device geometry favorable for fabrication (gate on top), this charge sheet

3080-534: The 1.9–3.53 μeV range. From 2013 to 2018 a series of upgrades were done and it is taking new data, including at 4.9–6.2 μeV. In December 2021 it excluded the 3.3–4.2 μeV range for the KSVZ model. Other experiments of this type include DMRadio, HAYSTAC, CULTASK, and ORGAN. HAYSTAC completed the first scanning run of a haloscope above 20 μeV in the late 2010s. The Italian PVLAS experiment searches for polarization changes of light propagating in

3168-524: The AlGaAs barrier to attract the electrons towards the gate, which forms the 2D electron gas and enables conduction of electron currents. This behaviour is similar to that of commonly used field-effect transistors in the enhancement mode, and such a device is called enhancement HEMT, or eHEMT . When a HEMT is built from AlGaN / GaN , higher power density and breakdown voltage can be achieved. Nitrides also have different crystal structure with lower symmetry, namely

3256-466: The AlGaAs layer are transferred to the undoped GaAs layer where they form a two dimensional high mobility electron gas within 100 ångström (10 nm ) of the interface. The n-type AlGaAs layer of the HEMT is depleted completely through two depletion mechanisms: The Fermi level of the gate metal is matched to the pinning point, which is 1.2 eV below the conduction band. With the reduced AlGaAs layer thickness,

3344-459: The Center for Experimental Physics and Astrophysics (CENPA) at the University of Washington . Led by Dr. Leslie Rosenberg, ADMX is undergoing an upgrade that will allow it to be sensitive to a broad range of plausible dark matter axion masses and couplings. The experiment is designed to detect the weak conversion of dark matter axions into microwave photons in the presence of a strong magnetic field. If

3432-550: The Earth's magnetic field of axions streaming from the Sun. Studying 15 years of data by the European Space Agency 's XMM-Newton observatory, a research group at Leicester University noticed a seasonal variation for which no conventional explanation could be found. One potential explanation for the variation, described as "plausible" by the senior author of the paper, is the known seasonal variation in visibility to XMM-Newton of

3520-484: The PQ field randomise the axion field, with no preferred value in the power spectrum. The proper treatment in this scenario is to solve numerically the equation of motion of the PQ field in an expanding Universe, in order to capture all features coming from the misalignment mechanism, including the contribution from topological defects like "axionic" strings and domain walls . An axion mass estimate between 0.05 and 1.50 meV

3608-406: The adjacent narrow band material’s conduction band due to the availability of states with lower energy. The movement of electrons will cause a change in potential and thus an electric field between the materials. The electric field will push electrons back to the wide band element’s conduction band. The diffusion process continues until electron diffusion and electron drift balance each other, creating

Axion Dark Matter Experiment - Misplaced Pages Continue

3696-462: The apparatus to 100 mK or less, reducing the noise to 150 mK, which makes data taking 400 times faster. This makes it the "Definitive Experiment". The Haloscope at Yale Sensitive to Axion CDM, or HAYSTAC (formerly known as ADMX-High Frequency), hosted at Yale University , is using a Josephson Parametric Amplifier, 9 T magnet, and microwave cavity with radius of 5 cm and height 25 cm to search masses 19–24 μeV. ADMX-Orpheus

3784-465: The axion energy density. However, other bounds that come from isocurvature modes severely constrain this scenario, which require a relatively low-energy scale of inflation to be viable. If at least one of the conditions (a) or (b) is violated, the axion field takes different values within patches that are initially out of causal contact , but that today populate the volume enclosed by our Hubble horizon . In this scenario, isocurvature fluctuations in

3872-503: The axion field begins its evolution, depending on the following two conditions: Broadly speaking, one of the two possible scenarios outlined in the two following subsections occurs: If both (a) and (b) are satisfied, cosmic inflation selects one patch of the Universe within which the spontaneous breaking of the PQ symmetry leads to a homogeneous value of the initial value of the axion field. In this "pre-inflationary" scenario, topological defects are inflated away and do not contribute to

3960-457: The axion field moves. Expanding the potential about one of its minima, one finds that the product of the axion mass with the axion decay constant is determined by the topological susceptibility of the QCD vacuum. An axion with mass much less than 60 keV is long-lived and weakly interacting: A perfect dark matter candidate. The oscillations of the axion field about the minimum of the effective potential,

4048-437: The axion has both a scalar and a fermionic superpartner . The fermionic superpartner of the axion is called the axino , the scalar superpartner is called the saxion or dilaton . They are all bundled in a chiral superfield . HFET A high-electron-mobility transistor ( HEMT or HEM FET ), also known as heterostructure FET ( HFET ) or modulation-doped FET ( MODFET ), is a field-effect transistor incorporating

4136-557: The axion itself. Despite not yet having been found, the axion has been well studied for over 40 years, giving time for physicists to develop insight into axion effects that might be detected. Several experimental searches for axions are presently underway; most exploit axions' expected slight interaction with photons in strong magnetic fields. Axions are also one of the few remaining plausible candidates for dark matter particles, and might be discovered in some dark matter experiments. Several experiments search for astrophysical axions by

4224-539: The axion mass to be placed from observations of neutron stars in gamma-rays using the Fermi Gamma-ray Space Telescope . From an analysis of four neutron stars, Berenji et al. (2016) obtained a 95% confidence interval upper limit on the axion mass of 0.079 eV. In 2021 it has been also suggested that a reported excess of hard X-ray emission from a system of neutron stars known as the magnificent seven could be explained as axion emission. In 2016,

4312-543: The axion, such as the axion mass, decay constant, and abundance, all have implications for cosmology. Inflation theory suggests that if they exist, axions would be created abundantly during the Big Bang . Because of a unique coupling to the instanton field of the primordial universe (the " misalignment mechanism "), an effective dynamical friction is created during the acquisition of mass, following cosmic inflation . This robs all such primordial axions of their kinetic energy. Ultralight axion (ULA) with m ~ 10 eV/ c

4400-661: The base material in MODFETs because of their better noise and power ratios. Ideally, the two different materials used for a heterojunction would have the same lattice constant (spacing between the atoms). In practice, the lattice constants are typically slightly different (e.g. AlGaAs on GaAs), resulting in crystal defects. As an analogy, imagine pushing together two plastic combs with a slightly different spacing. At regular intervals, you'll see two teeth clump together. In semiconductors, these discontinuities form deep-level traps and greatly reduce device performance. A HEMT where this rule

4488-403: The boundary of the two regions inside the narrow band gap material. The accumulation of electrons leads to a very high current in these devices. The term " modulation doping " refers to the fact that the dopants are spatially in a different region from the current carrying electrons. This technique was invented by Horst Störmer at Bell Labs . MODFETs can be manufactured by epitaxial growth of

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4576-453: The cavity are amplified by a Superconducting QUantum Interference Device (SQUID) amplifier followed by ultralow noise cryogenic HFET amplifiers. The receiver then downconverts microwave cavity frequencies to a lower frequency that can be easily digitized and saved. The receiver chain is sensitive to powers smaller than 10 rontowatts; this is the world's lowest-noise microwave receiver in a production environment. In 2010, ADMX eliminated one of

4664-423: The conduction and valence bands can be modified separately. This allows the type of carriers in and out of the device to be controlled. As HEMTs require electrons to be the main carriers, a graded doping can be applied in one of the materials, thus making the conduction band discontinuity smaller and keeping the valence band discontinuity the same. This diffusion of carriers leads to the accumulation of electrons along

4752-464: The conduction band on the GaAs side where the electrons can move quickly without colliding with any impurities because the GaAs layer is undoped, and from which they cannot escape. The effect of this is the creation of a very thin layer of highly mobile conducting electrons with very high concentration, giving the channel very low resistivity (or to put it another way, "high electron mobility"). Since GaAs has higher electron affinity , free electrons in

4840-407: The dark matter accounting for the bulk of all matter in our universe is axions, ADMX is one of only a few experiments able to detect it. Pierre Sikivie invented the axion haloscope in 1983. After smaller scale experiments at the University of Florida demonstrated the practicality of the axion haloscope, ADMX was constructed at Lawrence Livermore National Laboratory in 1995. In 2010 ADMX moved to

4928-439: The defense industry. The applications of HEMTs include microwave and millimeter wave communications , imaging, radar , radio astronomy , and power switching . They are found in many types of equipment ranging from cellphones, power supply adapters and DBS receivers to radio astronomy and electronic warfare systems such as radar systems. Numerous companies worldwide develop, manufacture, and sell HEMT-based devices in

5016-507: The electrodynamic equations are: Above, a dot above a variable denotes its time derivative; the dot spaced between variables is the vector dot product ; the factor   g a γ γ   {\displaystyle \ g_{a\gamma \gamma }\ } is the axion-to-photon coupling constant rendered in "natural units". Alternative forms of these equations have been proposed, which imply completely different physical signatures. For example, Visinelli wrote

5104-667: The electrodynamics of these materials. This term leads to several interesting predicted properties including a quantized magnetoelectric effect . Evidence for this effect has been given in THz spectroscopy experiments performed at the Johns Hopkins University on quantum regime thin film topological insulators developed at Rutgers University . In 2019, a team at the Max Planck Institute for Chemical Physics of Solids published their detection of an axion insulator phase of

5192-418: The electrons supplied by donors in the AlGaAs layer are insufficient to pin the layer. As a result, band bending is moving upward and the two-dimensional electrons gas does not appear. When a positive voltage greater than the threshold voltage is applied to the gate, electrons accumulate at the interface and form a two-dimensional electron gas. An important aspect of HEMTs is that the band discontinuities across

5280-687: The form of discrete transistors, as 'monolithic microwave integrated circuits' ( MMICs ), or within power switching integrated circuits. HEMTs are suitable for applications where high gain and low noise at high frequencies are required, as they have shown current gain to frequencies greater than 600 GHz and power gain to frequencies greater than 1THz. Gallium nitride based HEMTs are used as power switching transistors for voltage converter applications due to their low on-state resistances, low switching losses, and high breakdown strength. These gallium nitride enhanced voltage converter applications include AC adapters , which benefit from smaller package sizes due to

5368-496: The formation of a two-dimensional electron gas ( 2DEG ) are known as HEMTs. In HEMTS electric current flows between a drain and source element via the 2DEG, which is located at the interface between two layers of differing band gaps , termed the heterojunction . Some examples of previously explored heterojunction layer compositions (heterostructures) for HEMTs include AlGaN/GaN, AlGaAs/GaAs, InGaAs/GaAs, and Si/SiGe. The advantages of HEMTs over other transistor architectures, like

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5456-535: The galactic scale. If they continuously fall into galaxies from the intergalactic medium, they would be denser in " caustic " rings, just as the stream of water in a continuously flowing fountain is thicker at its peak. The gravitational effects of these rings on galactic structure and rotation might then be observable. Other cold dark matter theoretical candidates, such as WIMPs and MACHOs , could also form such rings, but because such candidates are fermionic and thus experience friction or scattering among themselves,

5544-426: The heterojunction of a highly doped wide-bandgap n-type donor-supply layer (AlGaAs in our example) and a non-doped narrow-bandgap channel layer with no dopant impurities (GaAs in this case). The electrons generated in the thin n-type AlGaAs layer drop completely into the GaAs layer to form a depleted AlGaAs layer, because the heterojunction created by different band-gap materials forms a quantum well (a steep canyon) in

5632-477: The hypothesis is correct, an apparatus consisting of an 8  tesla magnet and a cryogenically cooled high-Q tunable microwave cavity should stimulate the conversion of axions into photons. When the cavity's resonant frequency is tuned to the axion mass, the interaction between nearby axions in the Milky Way halo and ADMX's magnetic field is enhanced. This results in the deposit of a tiny amount of power (less than

5720-494: The implied dark matter density 0.3 ± 0.1 GeV/cm , indicating said axions would not have enough mass to be the sole component of dark matter. The ORGAN experiment plans to conduct a direct test of this result via the haloscope method. Dark matter cryogenic detectors have searched for electron recoils that would indicate axions. CDMS published in 2009 and EDELWEISS set coupling and mass limits in 2013. UORE and XMASS also set limits on solar axions in 2013. XENON100 used

5808-438: The improved detector allows a more sensitive search. The microwave cavity within the magnet bore is at the heart of ADMX. It is a circular cylinder, 1 meter long and 0.5 meter diameter. ADMX searches for axions by slowly scanning the cavity resonant frequency by adjusting positions of two tuning rods within the cavity. A signal appears when the cavity resonant frequency matches the axion mass. The expected signal from axion decay

5896-422: The low coupling constant thus predicts that the axion is not scattered out of its state despite its small mass so that the universe would be filled with a very cold Bose–Einstein condensate of primordial axions. Hence, axions could plausibly explain the dark matter problem of physical cosmology . Observational studies are underway, but they are not yet sufficiently sensitive to probe the mass regions if they are

5984-462: The noise (to less than 100 mK) and vastly improved sensitivity. ADMX has demonstrated that the SQUID amplifier allows for quantum-limited-power sensitivity. In 2016, ADMX acquired Josephson Parametric Amplifiers which allow quantum noise limited searches at higher frequencies. The addition of a dilution refrigerator was the main focus of the 2016 upgrade program. The dilution refrigerator allows cooling

6072-581: The nuclear spin rotation occurs. This precession can be measured using precession magnetometry and if detected, would be evidence for Axions. An experiment using this technique is the Cosmic Axion Spin Precession Experiment (CASPEr). Axions may also be produced at colliders, in particular in electron-positron collisions as well as in ultra-peripheral heavy ion collisions at the Large Hadron Collider at CERN, reinterpreting

6160-400: The observation that the strong force holding nuclei together and the weak force making nuclei decay differ in the amount of CP violation in their interactions. Weak interaction was expected to feed into the strong interactions ( QCD ), yielding appreciable QCD CP violation, but no such violation has been observed to very high accuracy. One solution to this Strong CP Problem introduces

6248-479: The other side of the barrier. Experiments by BFRS and a team led by Rizzo ruled out an axion cause. GammeV saw no events, reported in a 2008 Physics Review Letter. ALPS I conducted similar runs, setting new constraints in 2010; ALPS II began collecting data in May 2023. OSQAR found no signal, limiting coupling, and will continue. Axion-like bosons could have a signature in astrophysical settings. In particular, several works have proposed axion-like particles as

6336-549: The photon production, necessary to allow the X-rays to enter the detector that cannot point directly at the sun, would dissipate the flux so much that the probability of detection would be negligible. In 2013, Christian Beck suggested that axions might be detectable in Josephson junctions ; and in 2014, he argued that a signature, consistent with a mass ≈110 μeV, had in fact been observed in several preexisting experiments. In 2020,

6424-551: The polarized light measurements of Messier 87* by the Event Horizon Telescope were used to constrain the mass of the axion assuming that hypothetical clouds of axions could form around a black hole, rejecting the approximate 10  eV/ c – 10  eV/ c range of mass values. Resonance effects may be evident in Josephson junctions from a supposed high flux of axions from the galactic halo with mass of 110 μeV and density 0.05 GeV/cm compared to

6512-475: The possibility of new particle discovery. One theory of axions relevant to cosmology had predicted that they would have no electric charge , a very small mass in the range from 1 μeV/ c to 1 eV/ c , and very low interaction cross-sections for strong and weak forces. Because of their properties, axions would interact only minimally with ordinary matter. Axions would also change to and from photons in magnetic fields. The properties of

6600-498: The power circuitry requiring smaller passive electronic components. The invention of the high-electron-mobility transistor (HEMT) is usually attributed to physicist Takashi Mimura (三村 高志), while working at Fujitsu in Japan. The basis for the HEMT was the GaAs (gallium arsenide) MOSFET (metal–oxide–semiconductor field-effect transistor), which Mimura had been researching as an alternative to

6688-428: The rings would be less sharply defined. João G. Rosa and Thomas W. Kephart suggested that axion clouds formed around unstable primordial black holes might initiate a chain of reactions that radiate electromagnetic waves, allowing their detection. When adjusting the mass of the axions to explain dark matter, the pair discovered that the value would also explain the luminosity and wavelength of fast radio bursts , being

6776-505: The role of Θ , naturally relaxing the CP-violation parameter to zero. Wilczek named this new hypothesized particle the "axion" after a brand of laundry detergent because it "cleaned up" a problem, while Weinberg called it "the higglet". Weinberg later agreed to adopt Wilczek's name for the particle. Because it has a non-zero mass, the axion is a pseudo-Nambu–Goldstone boson . QCD effects produce an effective periodic potential in which

6864-441: The same without dark matter. Approximately five times more abundant than ordinary matter, the nature of dark matter remains one of the biggest mysteries in physics. In addition to solving the strong CP problem , the axion could provide an answer to the question "what is dark matter made of?" The axion is a neutral particle that is extraordinarily weakly interacting and could be produced in the right amount to constitute dark matter. If

6952-494: The so-called misalignment mechanism, generate a cosmological population of cold axions with an abundance depending on the mass of the axion. With a mass above 5  μeV/ c (10 times the electron mass ) axions could account for dark matter , and thus be both a dark-matter candidate and a solution to the strong CP problem. If inflation occurs at a low scale and lasts sufficiently long, the axion mass can be as low as 1 peV/ c . There are two distinct scenarios in which

7040-431: The solution to the dark matter problem with the fuzzy dark matter region starting to be probed via superradiance . High mass axions of the kind searched for by Jain and Singh (2007) would not persist in the modern universe. Moreover, if axions exist, scatterings with other particles in the thermal bath of the early universe unavoidably produce a population of hot axions. Low mass axions could have additional structure at

7128-566: The standard silicon (Si) MOSFET since 1977. He conceived the HEMT in Spring 1979, when he read about a modulated-doped heterojunction superlattice developed at Bell Labs in the United States, by Ray Dingle, Arthur Gossard and Horst Störmer who filed a patent in April 1978. Mimura filed a patent disclosure for a HEMT in August 1979, and then a patent later that year. The first demonstration of

7216-478: The standard model, QCD, possess a non-trivial vacuum structure that in principle permits violation of the combined symmetries of charge conjugation and parity , collectively known as CP. Together with effects generated by weak interactions , the effective periodic strong CP-violating term, Θ , appears as a Standard Model input – its value is not predicted by the theory, but must be measured. However, large CP-violating interactions originating from QCD would induce

7304-474: The sunward magnetosphere in which X-rays may be produced by axions from the Sun's core. This interpretation of the seasonal variation is disputed by two Italian researchers, who identify flaws in the arguments of the Leicester group that are said to rule out an interpretation in terms of axions. Most importantly, the scattering in angle assumed by the Leicester group to be caused by magnetic field gradients during

7392-448: The transient signal from the encounter between a neutron star and an axion minicluster in the Milky Way . Axions can be produced in the Sun's core when X-rays scatter in strong electric fields. The CAST solar telescope is underway, and has set limits on coupling to photons and electrons. Axions may also be produced within neutron stars by nucleon–nucleon bremsstrahlung . The subsequent decay of axions to gamma rays allows constraints on

7480-522: The two axion benchmark models from 1.9 μeV to 3.53 μeV, assuming axions saturate the Milky Way's halo. A 2016 upgrade should allow the ADMX to exclude or discover 1 μeV to 40 μeV dark matter axions. In the first implementation of the experiment in 1996, the amplifier noise temperature was around 2 K. In 2009, the first stage amplifier was replaced by a SQUID amplifier, which greatly lowered

7568-496: Was presented by Delagebeaudeuf and Nuyen in August 1980. One of the earliest mentions of a GaN-based HEMT is in the 1993 Applied Physics Letters article, by Khan et al . Later, in 2004, P.D. Ye and B. Yang et al demonstrated a GaN (gallium nitride) metal–oxide–semiconductor HEMT (MOS-HEMT). It used atomic layer deposition (ALD) aluminum oxide (Al 2 O 3 ) film both as a gate dielectric and for surface passivation . Field effect transistors whose operation relies on

7656-647: Was reported by Borsanyi et al. (2016). The result was calculated by simulating the formation of axions during the post-inflation period on a supercomputer . Progress in the late 2010s in determining the present abundance of a KSVZ-type axion using numerical simulations lead to values between 0.02 and 0.1 meV, although these results have been challenged by the details on the power spectrum of emitted axions from strings. The axion models originally proposed by Wilczek and by Weinberg chose axion coupling strengths that were so strong that they would have already been detected in prior experiments. It had been thought that

7744-546: Was shown that any very light axion would have been overproduced in the early universe and therefore must be excluded. Pierre Sikivie computed how Maxwell's equations are modified in the presence of an axion in 1983. He showed that these axions could be detected on Earth by converting them to photons, using a strong magnetic field, motivating a number of experiments. For example, the Axion Dark Matter Experiment converts axion dark matter to microwave photons,

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