PVLAS
PVLAS (Polarizzazione del Vuoto con LASer, "polarization of the vacuum with laser") aims to carry out a test of quantum electrodynamics and possibly detect dark matter at the Department of Physics and National Institute of Nuclear Physics in Ferrara, Italy. It searches for vacuum polarization causing nonlinear optical behavior in magnetic fields. Experiments began in 2001 at the INFN Laboratory in Legnaro (Padua, Italy) and continue today with new equipment. Background Nonlinear electrodynamic effects in vacuum have been predicted since the earliest days of quantum electrodynamics (QED), a few years after the discovery of positrons. One such effect is vacuum magnetic birefringence, closely connected to elastic light-by-light interaction. The effect is extremely small and has never yet been observed directly. Although today QED is a very well-tested theory, the importance of detecting light-by-light interaction remains. First, QED has always been tested in the presence of charged ...
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Photon-photon Scattering
Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear effects. In pure vacuum, some weak scattering of light by light exists as well. Also, above some threshold of this center-of-mass energy of the system of the two photons, matter can be created. Astronomy Cosmological/intergalactic gamma rays Photon–photon interactions limit the spectrum of observed gamma-ray photons at moderate cosmological distances to a photon energy below around 20 GeV, that is, to a wavelength of greater than approximately . This limit reaches up to around 20 TeV at merely