1. Anisimov, A., Babichev, E., Vikman, A.: J. Cosmol. Astropart. Phys. 6, 006 (2005)
2. Armendáriz-Picón, C., Mukhanov, V., Steinhardt, P.J.: Phys. Rev. D 63, 103510 (2001)
3. Avelino, C., Beca, L.M.G., de Carvalho, J.P.M., Martins, C.J.A.P., Pinto, P.: Phys. Rev. D, Part. Fields 67, 023511 (2003)
4. Bali, R., Singh, J.P.: Int. J. Theor. Phys. 47, 3288 (2008)
5. Bennett, C.L., et al.: Astrophys. J. Suppl. Ser. 148, 1 (2003)