Horizon structure of rotating Bardeen black hole and particle acceleration

We investigate the horizon structure and ergosphere in a rotating Bardeen regular black hole, which has an additional parameter ($g$) due to magnetic charge, apart from mass ($M$) and rotation parameter ($a$). Interestingly, for each value of parameter $g$, there exist a critical rotation parameter ($a=a_{E}$), which corresponds to an extremal black hole with degenerate horizons, while for $a<a_{E}$ describes a non-extremal black hole with two horizons, and no black hole for $a>a_{E}$. We find that the extremal value $a_E$ is also influenced by the parameter $g$ and so is the ergosphere. While the value of $a_E$ remarkably decreases when compared with the Kerr black hole, the ergosphere becomes more thick with increase in $g$. We also study collision of two equal mass particle near the horizon of this black hole, and explicitly bring out the effect of parameter $g$. The center-of-mass energy ($E_{CM}$) not only depends on rotation parameter $a$, but also on parameter $g$. It is demonstrated that the $E_{CM}$ could be arbitrary high in the extremal cases when one of the colliding particle has critical angular momentum, thereby suggesting that the rotating Bardeen regular black hole can act as a particle accelerator.