1. C L Bennett, et al., [WMAP Collaboration], arXiv:1212.5225 [astro-ph.CO].
2. G Hinshaw, et al., [WMAP Collaboration] arXiv:1212.5226 [astro-ph.CO].
3. P A R Ade, et al., [Planck Collaboration], arXiv:1303.5076 [astroph.CO].
4. M S Turner and L M Widrow, Phys. Rev. D 37, (1988) 2743.
5. B Ratra, Astrophys. J. 391, (1992) L1.
6. J Soda, Class. Quant. Grav. 29, (2012) 083001.
7. M a. Watanabe, S Kanno and J Soda, Phys. Rev. Lett. 102, (2009) 191302.
8. N Bartolo, S Matarrese, M Peloso, and A Ricciardone, Phys. Rev. D 87 (2013) 023504.
9. J Kim, E Komatsu, Phys. Rev. D 88, (2013) 101301.
10. S Weinberg, Phys. Rev. D 77, (2008) 12.
11. M. a. Watanabe, S. Kanno, and J. Soda, Prog. Theor. Phys. 123, (2010) 1041.
12. R Emami and H Firouzjahi, JCAP 1310, (2013) 041.
13. A A Abolhasani, M Akhshik, and H Firouzjahi, JCAP 1603, (2016) 03.