SL(2,C)in an Infinite-MomentumE(2)Basis and the Calculation of Form Factors

In the infinite-momentum limit the $E\left(2\right)\mathrm{}$ subgroup of the homogeneous Lorentz group $\mathrm{SL}(2,C)\mathrm{}$ becomes meaningful. It is shown that this decomposition of $\mathrm{SL}(2,C)\mathrm{}$ in an $E\left(2\right)\mathrm{}$ basis is also useful in calculations of form factors involving the $\mathrm{SL}(2,C)\mathrm{}$ group. In particular, the Barut-Kleinert and Nambu form factors are derived in a straightforward fashion.