电磁场中光子-轴子的转化微分截面

Conversion cross section between photon and axion in external electromagnetic field

运用费曼微扰方法分别计算了在磁偶极场、电偶极场和均匀静电场及静磁场中光子转化成轴子的非极化微分截面.在电偶极场中,沿光子传播方向及其反方向上的非极化微分截面为零;而在磁偶极场中,在上述方向上通常则具有非零的微分截面,但当光子传播方向平行于磁场偶极距矢量时,该微分截面为零.在均匀的静磁场和均匀静电场中,只有在光子传播方向及其反方向上具有非零的微分截面,但后者小于前者.在轴子质量趋于零的极限条件下,上述过程和光子转化为引力子的过程表现出某些非常类似的性质.

We calculate the unpolarized differential cross section in magnetic dipole field, electric dipole field and uniform electrostatic and magnetostatic fields, respectively, by the Feynman perturbation technique. It is found that in electric dipole field, the differential cross section vanishes in both the same and the opposite propagating directions of the photon flux. In the magnetic dipole field the differential cross section generally has non-vanishing values in both directions, but when the propagating direction of photon flux is parallel to the magnetic dipole vector, the differential cross section is equal to zero. In the uniform electrostatic and magnetostatic fields, non-vanishing differential cross sections occur in the same and opposite propagating directions of the photon flux, but in the latter case it is weaker than in the former. When the mass of axion approaches to zero, the above process shows similar characters as the conversion of the photons to the gravitons.