The axion hunting

The axion is a neutral, light and very weakly interacting particle that was imagined in the seventies to unify some aspects of the basic interactions. Another important feature of axions is their capacity to transform themselves into photons when crossing a magnetic field, the probability of this conversion is very low, proportional to the intensity of the magnetic field and all the less low as the mass of the axion is tiny. Axions are perfect candidates to dark matter and could also explain why the solar corona is so hot. The magnetic fields inside the sun are so intense that they could enable axions to mutate into photons leading to an excess of energy and light in the out layers of the sun. Till now, no experiment has led to the detection of axions despite the announcement made in march 2006 of their discovery by an Italian team, these experimental results were unanimously acknowledged as biased. The ADMX program (Axion Dark Matter eXperiment) launched in the nineties, has led to constrains on the mass of the axions: the 1.9 - 3.3 eV range for the mass has been experimentally barred. Other experiments like CAST (CERN Axion Solar Telescope) have led to complementary constrains on the mass or to new constrains on the axion-photon coupling. (A.C.)