τ⁻to ell_i⁻ ell_i⁺ ell_j⁻ bar{ν}_(j) ν_(τ) decays with a magnetic dipole term

Using the massive helicity formalism we calculate the five-body average square amplitude of the decays $\tau^{-}\to \ell_i^{-} \ell_i^{+} \ell_j^{-} \bar{\nu}_{j} \nu_{\tau}$ $(\ell=e,\,\mu)$ within the Standard Model (SM), we then introduce a dimension-five effective vertex $\Gamma^{\tau\tau \gamma}$ in order to determine the feasibility of imposing limits on the tau anomalous magnetic dipole moment ($a_\tau$) via the current or future experimental measurements of the branching ratio for the decay $\tau^{-}\to e^{-} e^{+} e^{-} \bar{\nu}_{e} \nu_{\tau}$.