The axion (/ˈæksiɒn/) is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve 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.
|Theorized||1977, Peccei and Quinn|
|Mass||10−5 to 10−3 eV/c2 |
|Decay width||109 to 1012 GeV/c2 |
One simple solution exists: If at least one of the quarks of the standard model is massless, CP-violation becomes unobservable. However, empirical evidence strongly suggests that none of the quarks are massless. Consequently, particle theorists sought other resolutions to the problem of inexplicably conserved CP.
As shown by Gerard 't Hooft, strong interactions of 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 a large electric dipole moment (EDM) for the neutron. Experimental constraints on the currently unobserved EDM implies CP violation from QCD must be extremely tiny and thus Θ must itself be extremely small. Since a priori Θ could have any value between 0 and 2π, 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 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 symmetry) that becomes spontaneously broken. This results in a new particle, as shown by Frank Wilczek and Steven Weinberg, that fills the role of Θ, naturally relaxing the CP-violation parameter to zero. This hypothesized new particle is called the axion. The original Weinberg–Wilczek axion was ruled out.[a]
Axion models carefully chose coupling that could not have been detected in prior experiments. It had been thought that these “invisible axions” solved the strong CP problem while still being too small to have been observed before. Current literature discusses “invisible axion” mechanisms in two forms, called 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 was shown that any very light axion would have been overproduced in the early universe and therefore must be excluded. The critical mass is of order 10−11 times the electron mass.
With a mass above 10−11 times the electron mass, axions could account for dark matter, thus be both a dark-matter candidate and a solution to the strong CP problem. A mass value between 0.05 and 1.50 meV for the axion was reported in a paper published in November 2016 (Borsanyi, S. et al.). The result was calculated by simulating the formation of axions during the post-inflation period on a supercomputer.
Pierre Sikivie published a modification of Maxwell's equations that arise from a light, stable axion in 1983. He showed that these axions could be detected on Earth by converting them to photons, using a strong magnetic field, hence leading to several experiments: the ADMX; Solar axions may be converted to X-rays, as in CAST; Other experiments are searching laser light for signs of axions.
If magnetic monopoles exist then there is a symmetry in Maxwell's equations where the electric and magnetic fields can be rotated into each other with the new fields still satisfying Maxwell's equations. Luca Visinelli showed that the duality symmetry can be carried over to the axion-electromagnetic theory as well. Assuming the existence of both magnetic charges and axions, Maxwell's equations read
|Gauss's law for magnetism|
If magnetic monopoles do not exist, then the same equations hold with the density and current replaced by zero. Incorporating the axion has the effect of rotating the electric and magnetic fields into each other.
where the mixing angle depends on the coupling constant and the axion field strength
By plugging the new values for electromagnetic field and into Maxwell's equations we obtain the axion-modified Maxwell equations above. Incorporating the axion into the electromagnetic theory also gives a new differential equation – the axion law – which is simply the Klein-Gordon Equation (the quantum field theory equation for massive spin-zero particles) with an source term.
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 the electrodynamics of these materials. This term leads to several interesting predicted properties including a quantized magnetoelectric effect. Evidence for this effect has recently been given in THz spectroscopy experiments performed at the Johns Hopkins University.
The Italian PVLAS experiment searches for polarization changes of light propagating in 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, that pass through metal. Experiments by BFRS and a team led by Rizzo ruled out an axion cause. GammeV saw no events in a 2008 PRL. ALPS-I conducted similar runs, setting new constraints in 2010; ALPS-II will run in 2019. OSQAR found no signal, limiting coupling and will continue.
Several experiments search for astrophysical axions by the Primakoff effect, which converts axions to photons and vice versa in electromagnetic fields. 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. ADMX searches the galactic dark matter halo for resonant axions with a cold microwave cavity and has excluded optimistic axion models in the 1.9–3.53 μeV range. It is amidst a series of upgrades and is taking new data, including at 4.9–6.2 µeV. Other experiments of this type include HAYSTAC, CULTASK, and ORGAN. HAYSTAC recently completed the first scanning run of a haloscope above 20 µeV.
Resonance effects may be evident in Josephson junctions from a supposed high flux of axions from the galactic halo with mass of 0.11 meV and density 0.05 GeV⋅cm−3 compared to the implied dark matter density 0.3±0.1 GeV⋅cm−3, 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 a 225 day run to set the best coupling limits to date and exclude some parameters.
Axion-like bosons could have a signature in astrophysical settings. In particular, several recent works have proposed axion-like particles as a solution to the apparent transparency of the Universe to TeV photons. It has also been demonstrated in a few recent works 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 current telescopes. A new promising means 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 may be produced within neutron stars, by nucleon-nucleon bremsstrahlung. The subsequent decay of axions to gamma rays allows constraints on the axion mass to be placed from observations of neutron stars in gamma-rays using the Fermi LAT. From an analysis of four neutron stars, Berenji et al. obtained a 95% CL upper limit on the axion mass of 0.079 eV.
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 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 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 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 2016 a theoretical team from MIT devised a possible way of detecting axions using a strong magnetic field. The magnetic field need be no stronger than that produced in a MRI scanning machine and it should show a slight wavering variation that is linked to the mass of the axion. The experiment is now being implemented by experimentalists at the university. Another approach being used by the University of Washington uses a strong magnetic field to detect the possible weak conversion of axions to microwaves.
One theory of axions relevant to cosmology had predicted that they would have no electric charge, a very small mass in the range from 10−6 to 1 eV/c2, 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.
In supersymmetric theories 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 up in a chiral superfield.
Inflation suggests that axions were 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.
If axions have low mass, thus preventing other decay modes (since there's no lighter particles to decay into), theories predict 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 the solution to the dark matter problem. 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 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, the rings would be less pronounced.
Ultralight axion (ULA) with m ~ 10−22 eV is a kind of scalar field dark matter which 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 than other more massive dark particles. The lingering effects of this difference could perhaps be calculated and observed astronomically.
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 a possible origin for both phenomena.
possible early evidence of 7±1 and 19±1 MeV axions of less than 10−13 s lifetime
hypothetical flow diagram which could give rise to such a structure
The axino is a hypothetical elementary particle predicted by some theories of particle physics. Peccei–Quinn theory attempts to explain the observed phenomenon known as the strong CP problem by introducing a hypothetical real scalar particle called the axion. Adding supersymmetry to the model predicts the existence of a fermionic superpartner for the axion, the axino, and a bosonic superpartner, the saxion. They are all bundled up in a chiral superfield.
The axino has been predicted to be the lightest supersymmetric particle in such a model. In part due to this property, it is considered a candidate for the composition of dark matter.The supermultiplet containing an axion and axino has been suggested as the origin of supersymmetry breaking, where the supermultiplet gains an F-term expectation value.Axion (mythology)
In Greek mythology, Axion (Ancient Greek: Αξιόν) was the name of the following two individuals.
Axion, son of Phegeus of Psophis in Arcadia and brother of Temenus and Alphesiboea. At the command of their father, Axion together with his brother murdered by treachery their brother-in-law Alcmaeon and the two then dedicated the necklace of Harmonia to the god Apollo in Delphi. It is said that when the expedition of the Greeks to Troy took place, Axion and Temenus were the kings in the city that was still called Phegia (former name of Psophis). The people of Psophis assert that the reason why they took no part in the expedition was because their princes had incurred the enmity of the leaders of the Argives, who were in most cases related by blood to Alcmaeon, and had joined him in his campaign against Thebes. Later on, the widowed sister, Alphesiboea killed her own brothers in revenge of her husband's death. Otherwise, Apollodorus calls the two sons of Phegeus, Agenor and Pronous.
Axion, son of Priam of Troy, who was killed by Eurypylus, son of Euaemon during the Trojan War.Axion Dark Matter Experiment
The Axion Dark Matter Experiment (ADMX, also written as Axion Dark Matter eXperiment in the project's documentation) uses a resonant microwave cavity within a large superconducting magnet to search for cold dark matter axions in the local galactic dark matter halo. Unusually for a dark matter detector, it is not located deep underground. Sited at the Center for Experimental Nuclear Physics and Astrophysics (CENPA) at the University of Washington, ADMX is a large collaborative effort with researchers from universities and laboratories around the world.Axion Estin
Axion estin (Greek: Ἄξιον ἐστίν, Slavonic: Достóйно éсть, Dostóino yesť), or It is Truly Meet, is a megalynarion and a theotokion, i.e. a magnification of and a Hymn to Mary which is chanted in the Divine Services of the Eastern Orthodox and Eastern Catholic Churches. It is a troparion and a sticheron composed in honor of the Theotokos (i.e. the Virgin Mary). The same name also refers to a style of icon of the Theotokos.CERN Axion Solar Telescope
The CERN Axion Solar Telescope (CAST) is an experiment in astroparticle physics to search for axions originating from the Sun. The experiment, sited at CERN in Switzerland, came online in 2002 with the first data-taking run starting in May 2003. The successful detection of solar axions would constitute a major discovery in particle physics, and would also open up a brand new window on the astrophysics of the solar core.
If the axions exist, they may be produced in the Sun's core when X-rays scatter off electrons and protons in the presence of strong electric fields. The experimental setup is built around a 9.26 m long decommissioned test magnet for the LHC capable of producing a field of up to 9.5 T. This strong magnetic field is expected to convert solar axions back into X-rays for subsequent detection by X-ray detectors. The telescope observes the Sun for about 1.5 hours at sunrise and another 1.5 hours at sunset each day. The remaining 21 hours, with the instrument pointing away from the Sun, are spent measuring background axion levels.
CAST began operation in 2003 searching for axions up to 0.02 eV. In 2005, Helium-4 was added to the magnet, extending sensitivity to masses up to 0.39 eV, then Helium-3 was used during 2008–2011 for masses up to 1.15 eV. CAST then ran with vacuum again searching for axions below 0.02 eV.
As of 2014, CAST has not turned up definitive evidence for solar axions. It has considerably narrowed down the range of parameters where these elusive particles may exist. CAST has set significant limits on axion coupling to electrons and photons.A 2017 paper using data from the 2013-2015 run reported a new best limit on axion-photon coupling of 0.66E-10 / GeV.Built upon the experience of CAST, a much larger, new-generation, axion helioscope, the International Axion Observatory (IAXO), has been proposed and is now under preparation.Cable Axion
Cable Axion is a cable television distributor and Internet service provider based at Magog, Quebec.Charline Labonté
Charline Labonté (born October 15, 1982) is a Canadian retired professional ice hockey player. Labonté played professionally for the Montreal Stars/Les Canadiennes de Montreal of the Canadian Women's Hockey League. She was a member of the Canada women's national ice hockey team that won three gold medals at the Olympics and two gold medals in the World Championships. She is an alumnus of the McGill Martlets hockey program.
Labonté now lives in Montreal, and graduated from McGill University with a degree in Physical Education. Labonté was named to the 2014 Olympic roster for Canada. She would be the winning goaltender for Les Canadiennes de Montreal in the final of the 2017 Clarkson Cup. In September 2017, she retired from Les Canadiennes and the Canadian national hockey team, as the goalie ranking second most all-time in games won (45), shutouts (16), and games played for Canada, with three Olympic gold medals, 2 world championship wins and 6 world silver medals.Colgate-Palmolive
Colgate-Palmolive Company is an American worldwide consumer products company focused on the production, distribution and provision of household, health care, and personal care products. Under its "Hill's Pet Nutrition" brand, it is also a manufacturer of veterinary products. The company's corporate offices are on Park Avenue in Midtown Manhattan, New York City.Gina Kingsbury
Gina Kingsbury (born November 26, 1981 in Uranium City, Saskatchewan) is a retired women's ice hockey player. She graduated from St. Lawrence University with a degree in psychology. She ranks second all-time in scoring among St. Lawrence Skating Saints women's ice hockey players.Jesse Scanzano
Jesse Scanzano (born October 15, 1988) is a Canadian ice hockey forward for the Mercyhurst College Lakers. She grew up in Montreal, Quebec and played for the Montreal Axion women's ice hockey team and participated in the 2005 Esso Women’s Nationals She was selected fifth overall in the 2011 CWHL Draft. Scanzano played for the 2011–12 Canada women's national ice hockey team and appeared in the 2011 4 Nations Cup.
For 2011-12 season, she plays for Toronto Furies of the Canadian Women's Hockey League.Kareem Campbell
Kareem Campbell (born November 14, 1973) is a professional skateboarder. He is known popularizing the skateboard trick "The Ghetto Bird" which is a nollie hardflip late 180°. He was born in Harlem, New York. Throughout his career Kareem has been sponsored by World Industries, Axion shoes, Nixon watches, Alphanumeric clothing and more.Montreal Axion
The Montreal Axion were a National Women's Hockey League team (2003 to 2007) located in Montreal, Quebec, Canada. The Axion represented Quebec at the 2005 Esso Women's Nationals. They were previously known as Bonaventure Wingstar (1998–99) and Montreal Wingstar (1999–2003). This team was succeeded as the women's professional hockey team of Montreal by the Montreal Stars in the Canadian Women's Hockey League, starting with the 2007–2008 season.Nicholas II of Constantinople
Nicholas II Chrysoberges (Greek: Νικόλαος ὁ Χρυσοβέργης), (? – 16 December 991) was Ecumenical Patriarch of Constantinople from 984 to 991.
In 980, during the reign of Emperor Basil II, when Nicholas Chrysoberges was Ecumenical Patriarch, the Archangel Gabriel was believed to have appeared in the guise of a monk to the disciple of a certain monk at the Monastery of the Pantocrator in Mount Athos. The monk reported that the angel sang a new verse of the matins hymn, recorded on a slate still held at the monastery. Nicholas received the relic in the cathedral of Hagia Sophia. The Axion Estin is still sung in Orthodox services.
Nicholas' tenure also saw the completion of the Christianization of the Rus' and the appointment of the first metropolitan for Rus', Michael the Syrian.
Patriarch Nicholas was later canonized and is commemorated by both the Roman Catholic Church and the Orthodox Church on December 16.Papilio euchenor
Papilio euchenor is a butterfly of the family Papilionidae.Peccei–Quinn theory
In particle physics, the Peccei–Quinn theory is a well-known proposal for the resolution of the strong CP problem. It was formulated by Roberto Peccei and Helen Quinn. The theory proposes that the QCD Lagrangian be extended with a CP-violating term known as “the θ term”. Because experiments have never measured a value for θ, its value must be very nearly zero.Torsion field (pseudoscience)
A torsion field (also called axion field, spin field, spinor field, and microlepton field) is a feature of pseudoscientific proposals that the quantum spin of particles can be used to cause emanations to carry information through vacuum orders of magnitude faster than the speed of light. This theory is the basis of a number of unfounded claims and scams.Willy Fischler
Willy Fischler (born 1949 in Antwerpen, Belgium) is a theoretical physicist. He is the Jane and Roland Blumberg Centennial Professor of Physics at the University of Texas at Austin, where he is affiliated with the Weinberg theory group. His contributions to physics include:
Early computation of the force between heavy quarks.
The invisible axion (see Axion), (with Michael Dine and Mark Srednicki) as a solution to the strong CP problem.
The cosmological effects of the invisible axion (with Michael Dine) and its role as a candidate for dark matter.
Pioneering work (with Michael Dine and Mark Srednicki) on the use of supersymmetry to solve outstanding problems in the standard model of particle physics.
The first formulation of what became known as the "moduli problem in cosmology" (with G.D. Coughlan, Edward Kolb, Stuart Raby and Graham Ross).
The Fischler-Susskind mechanism in string theory (with Leonard Susskind).
The original formulation of the holographic entropy bound in the context of cosmology (with Leonard Susskind).
The discovery of M(atrix) theory, or BFSS Matrix Theory. M(atrix) theory is an example of a gauge/gravity duality (with Tom Banks, Steve Shenker and Leonard Susskind).
Black Hole production in colliders (with Tom Banks).He is a Licensed Paramedic with Marble Falls Area EMS and was a volunteer EMT with the Westlake Fire Department.
|Forms of dark matter|
|Theories and objects|
|Potential dark galaxies|