Vacuum Birefringence Caused by Arbitrary Spin Particles

The propagation of a linearly polarized laser beam in the external transverse magnetic field is studied. We take into consideration the vacuum polarization by arbitrary spin particles. With the help of the effective Lagrangian, Stokes parameters and induced ellipticity are evaluated. It is shown that ellipticity measured in the PVLAS experiment can be caused by charged spin-3/2 particles possessing the mass m3/2 = 0.22 MeV. However, there is no the polarization plane rotation (dichroism) to first order calculations. The results of the PVLAS experiment [1], measuring the vacuum birefringence and dichroism, can not be explained by quantum electrodynamics [2], [3]. This indicates onnphysics beyond the Standard Model. Two possible scenarios to treat the PVLAS experiment was suggested [4]: the existence of a new axion-like (spin-0) particle (ALP) [5] and millicharged particles (MCPs) [6]. Parameters of ALP exclude the identity of a new neutral light spin-0 boson and QCD axion [4]. Besides, the model of ALP is non-renormalizable because it contains the dimensional coupling constant. Although MCPs scenario does not possess this negative attribute, it seems questionable the existence of a charge which is much less (10) than the charge of the electron e. It is reasonable, therefore, to look for the alternative to ALP and MCPs scenarios. In this letter, we study vacuum birefringence caused by higher spin particles. In [7], [8] the non-linear corrections to the Maxwell Lagrangian were calculated, taking into consideration the vacuum polarization of arbitrary spin particles possessing the electric dipole moment (EDM) and anomalous magnetic moment (AMM). Due to the small contribution of EDM of particles (violating the CP invariance) to physical quantities, we