Maximal subgroups of non-torsion Grigorchuk-Gupta-Sidki groups

A Grigorchuk-Gupta-Sidki (GGS-)group is a subgroup of the automorphism group of the p-regular rooted tree for an odd prime p, generated by one rooted automorphism and one directed automorphism. Pervova proved that all torsion GGS-groups do not have maximal subgroups of infinite index. Here we extend the result to non-torsion GGS-groups, which include the weakly regular branch, but not branch, GGS-group.