1. Wald RM (1984) General Relativity. Chicago: The University of Chicago Press
2. Landau LD; Lifshitz EM (1989) The Classical Theory of Fields, fourth revised edition. Oxford: Pergamon Press
3. Weinberg S (1972) Gravitation and Cosmology. New York: Wiley
4. Kolb EW; Turner MS (1994) The Early Universe. Reading, MA: Addison-Wesley
5. Faraoni V et al (1999) Conformal transformations in classical gravitational theories and in cosmology. Fund. Cosmic Phys. 20: 121