&= \Re S_{eff}^F + \Im S_{eff}^F \ , &(\REIM) \cr
\Re S_{eff}^F &\equiv - {1\over2}\ {\rm Sp} \ln
[\,\, \tilde{\slash D}^{\dagger}
\, \, \tilde{\slash D}\,] \ , &(\REIMa) \cr
\Im S_{eff}^F &\equiv - {1\over2}\ {\rm Sp} \ln
[\,\,\tilde{\slash D}\, /
\, \,\tilde{\slash D}^{\dagger}\,]
\ , &(\REIMb) \cr
}$$

The imaginary (anomalous) part is finite and does not need regularization. In addition, any regularization of this part of the action would break several important features of the model related to the anomalous structure. On the other hand, the real part is infinite and a regularization is necessary.

In order to compute the nucleon form factors we have to evaluate the expectation value of the electromagnetic current $j^{em}_{\mu}$. To this end we take into account the standard definition given by:

$$\langle j_{\mu}^{em}(0) \rangle \equiv
{1\over Z_0} \
{\delta Z'_{NJL}[A_{\mu}]\over \delta A_{\mu}(0)} \Bigg\vert_{A_{\mu}=0}
\equiv {1\over Z_0} \
\int {\cal D}R \ {\delta S_{eff} \over \delta
A_{\mu}(0)}\Bigg\vert_{A_{\mu}=0} \exp \lbrack -\, S_{eff} \rbrack
\ , \eqno(\CURR)$$

0.1where the generating functional $Z'_{NJL}$ is given by ().

As it was mentioned above the real part of the action diverges. To calculate the expression (), we introduce the Schwinger proper-time regularization of the action. In general, for an 