Axions
The axion is a hypothetical pseudoscalar particle, stable, neutral, and of very low mass, typically between μeV and meV. It was independently proposed by Weinberg and Wilczek (1978), two Nobel laureates in Physics, from the breaking of the new symmetry postulated by Peccei-Quinn (1977) to solve the problem of non-violation of the CP symmetry in quantum chromodynamics, one of the last sand grains of in the gear of the Standard Model of particle physics. The axion is also considered to be one of the leading cold dark dark matter candidates of the universe.
Image from Hubble Space Telescope (https://www.nasa.gov/image-article/dark-matter/) illustrating one of the key observational evidences of dark matter. Since dark matter is invisible, it is not possible to see it directly, but its gravitational effects can be observed. This false-color image can only be understood by considering the modeled dark matter ring superimposed in diffuse blue explaining the observed gravitational lensing effect. One hypothesis for the formation of this large dark matter ring suggests that it is a transient structure formed during the collision of two galaxy clusters about a billion years ago (https://iopscience.iop.org/article/10.1086/517498/pdf).
Many theories beyond the Standard Model of particle physics predict numerous axion-like particles with very low masses and interacting very weakly with ordinary matter. They are also relevent dark matter candidates and have been dubbed ALPs meaning axion-like particles, the term axion being reserved for the particle that solves the strong CP problem. Incidentally, the term axion was proposed by Wilczek in reference to the well-known laundry detergent for “cleaning the quantum chromodynamics of its major defect.” Namely, the axion makes it possible to explain the disappearance of the CP violation by the strong interaction observed today, while preserving this symetry violation at the beginning of the universe, which is essential to explain why matter was able to prevail over antimatter, why there is something rather than nothing and therefore ultimately why we are here as “stardust”.
Many experiments are searching axion and ALPs, including CAST at CERN for axions/ALPs produced in the sun, ADMX in the US for axions/ALPs present in the halo of our galaxy as dark matter and detectable in the laboratory, as well as light shining through wall experiments such as OSQAR at CERN among others. The common feature of all these experiments is the use of intense magnetic fields combined with state-of-the-art detectors looking for the conversion of axions/ALPs into photons.
The CNRS Grenoble, through its expertise, brings together key skills in the fields of intense magnetic fields, ultra-low temperatures and quantum amplifiers, to build state-of-the-art haloscopes for axion/ALP search. The GRAHal (Grenoble Axion Haloscopes) project was borned from a collaboration between LNCMI and Institut Néel as well as LPSC for the theory part.
More information :
– https://indico.in2p3.fr/event/33124/contributions/141966/
– https://agenda.infn.it/event/40078/contributions/240662/
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