Chargino production via Z-Boson Decay in a Strong Electromagnetic Field
  In the framework of MSSM the probability of $Z^0$-boson decay to charginos in a strong electromagnetic field, $Z^0\rightarrow \chi ^{+} \chi ^{-}$, is analyzed. The method of calculations employs exact solutions of relativistic wave equations for charginos in a crossed electromagnetic field. Analytic expression for the decay width $\Gamma(Z^{0}\rightarrow \chi ^{+} \chi ^{-})$ is obtained at an arbitrary value of the parameter $\varkappa=e m_Z^{-3}\sqrt{-(F_{\mu\nu}q^\nu)^2}$, which characterizes the external-field strength $F_{\mu\nu}$ and $Z^0$-boson momentum $q^{\nu}$. The process $Z^0\rightarrow \chi ^{+} \chi ^{-}$ is forbidden in vacuum for the case of relatively heavy charginos: $M_{\chi^{\pm}} > m_Z/2$. However in an intense electromagnetic background this reaction could take place in the region of superstrong fields ($\varkappa > 1$). 
Alexander V. Kurilin
hep-ph