Axions are hypothetical zero spin (scalar) particles whose existance has been postulated as part of an explanation of Charge/Parity symmetry of the strong force.
The Standard Model of Particle Physics provide no direct explanation as to why the product of Charge Conjugation and Parity are conserved by the strong force - experimental evidence (such as the absence of any electrical diple moment in the Neutron) suggest that CP is conserved to very high precision. An additional field and spontaniously broken symmetry provide a possible explanation, and the symmtery breaking process generates the Axion.
The mass of the Axion is not predicted and interest has grown as a possible candidate for the Universe's missing mass (dark matter).
Theory give no prediction of the mass of the Axion, but does suggest that it couples to the electromagnetic field in the presence of strong magnetic fields. It is possible that the mass lies in the microwave region (30 GHz corresponds to a mass of 1.24 10^-4 eV).
The MADMAX experiment aims to see evidence of such a coupling, and we have been privilaged to be able to help research in MPI for Physics in Munich define a beam of microwave radiation which will enter their very senstive radiometer, and - in a fully developed experimet - might contain a minute amount of excess black-body radaition over a narrow band of frequencies, indicating the conversion of Axions into electromagnetic energy.
An image of the TK-supplied corrugated horn - working from 18 to 26.5 GHz - and off-axis ellipsoidal mirror
which realises the simple Gaussian-Beam mode circuit given here