Coherent production/detection of light scalars/pseudoscalars and QED vacuum polarization

We searched for light scalars/pseudoscalars (e.g., axions) that couple to two photons using three different techniques: 1) Optical rotation, where a polarized laser beam enters a dipole magnetic field region. The production of scalars/pseudoscalars has an effect the rotation of the polarization which is detected by an analyzer system giving a limit gαγγ<3.6×10−7 GeV−1, for ma<10−3 eV. 2) Photon regeneration experiment, where the particles are generated in one magnet by the polarized laser beam, travel through a wall and reconvert back to the original photons inside another magnet where they are detected by a photomultiplier, giving a limit to gαγγ<6.7×10−7 GeV−1 for the same mass range as above. 3) Finally we searched for scalars/pseudoscalars coming from the sun, looking at the back of a dipole magnet pointing at the setting sun, with an x‐ray detector. The limit obtained this way is gαγγ<3.7×10−9 GeV−1, provided ma<0.1 eV.