1 Erratum to: Eur. Phys. J. C (2019) 79:739 https://doi.org/10.1140/epjc/s10052-019-7252-z

The original version of this article unfortunately contained a mistake. Due to a misunderstanding during the proof correction process, a minus-plus sign had been incorrectly inserted before the first term in the second line of Eq. (22). The correct Eq. (22) is given below.

The original article has been corrected.

$$\begin{aligned} \begin{aligned} \Gamma _1&{}\approx \pm ({1+\lambda ^2} ) \gamma ^1\pm {i\lambda }\, \mathbf 1 ,\nonumber \\ \Gamma _2&{} \approx \frac{d \lambda }{d z}\, \mathbf 1 \mp i\frac{d\lambda ^2}{d z}\gamma ^1 , \end{aligned} \end{aligned}$$
(22)