Uniqueness of timelike killing vector fields
Annales de l'I.H.P. Physique théorique, Volume 23 (1975) no. 3, p. 297-301
@article{AIHPA_1975__23_3_297_0,
     author = {Ihrig, E. and Sen, D. K.},
     title = {Uniqueness of timelike killing vector fields},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     publisher = {Gauthier-Villars},
     volume = {23},
     number = {3},
     year = {1975},
     pages = {297-301},
     zbl = {0316.53047},
     mrnumber = {389131},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1975__23_3_297_0}
}
Ihrig, E.; Sen, D. K. Uniqueness of timelike killing vector fields. Annales de l'I.H.P. Physique théorique, Volume 23 (1975) no. 3, pp. 297-301. http://www.numdam.org/item/AIHPA_1975__23_3_297_0/

[1] S. Kobayashi and K. Nomizu, Foundations of Differential Geometry, Vol. I, Interscience, 1963. | MR 152974 | Zbl 0119.37502

[2] L. Landau and E. Lifshitz, The Classical Theory of Fields, Pergamon, 1962. | MR 143451 | Zbl 0178.28704