Non-linear plane gravitational waves as space-time defectsF. L. Carneiro, S. C. Ulhoa, J. W. Maluf and J. F. da Rocha-NetoEur. Phys. J. C, 81 1 (2021) 67DOI: https://doi.org/10.1140/epjc/s10052-021-08862-x