[1] . Nature, 418, 34-35(2002).

[2] . Phys. Rev. D, 39, 683(1989).

[3] . Nucl. Phys. B, 717, 86-118(2005).

[4] . Living Rev. Rel., 8, 5(2005).

[5] . Nature, 424, 1019-1021(2003).

[6] . Phys. Rev. Lett., 79, 1432-1435(1997).

[7] . Phys. Lett. B, 668, 253-257(2008).

[8] . Grav. Cosmol., 16, 288-297(2010).

[9] . Phys. Rev. D, 78, 092006(2008).

[10] . Phys. Rev. Lett., 96, 051301(2006).

[11] . Int. J. Mod. Phys. D, 22, 1342014(2013).

[12] . Phys. Rev. Lett., 96, 060801(2006).

[13] . Phys. Rev. Lett., 100, 031101(2008).

[14] . Phys. Rev. D, 80, 105011(2009).

[15] . Phys. Rev. Lett., 103, 090401(2009).

[16] . Phys. Rev. D, 84, 084010(2011).

[17] . Phys. Rev. Lett., 91, 190403(2003).

[18] . Phys. Rev. D, 72, 016005(2005).

[19] . Astropart. Phys., 23, 203-209(2005).

[20] . Astropart. Phys., 19, 447-462(2003).

[21] . Phys. Rev. Lett., 100, 101101(2008).

[22] . Mod. Phys. Lett. A, 25, 1129-1136(2010).

[23] . Phys. Rev. D, 96, 083523(2017).

[24] . Nature, 424, 1019-1021(2003).

[25] . Phys. Rev. Lett., 96, 201101(2006).

[26] . Phys. Rev. D, 77, 016002(2008).

[27] . Astrophys. J., 689, L1-L4(2008).

[28] . Nature, 462, 331-334(2009).

[29] . Phys. Rev. D, 94, 104052(2016).

[30] . Phys. Lett. B, 556, 7-13(2003).

[31] . Phys. Rev. Lett., 96, 251802(2006).

[32] . Phys. Rev. Lett., 79, 2394-2397(1997).

[33] . Nature, 393, 763-765(1998).

[34] . Phys. Rev. D, 59, 124021(1999).

[35] . Phys. Rev. Lett., 84, 2318-2321(2000).

[36] . JHEP, 0203, 043(2002).

[37] . Phys. Rev. Lett., 80, 2508-2511(1998).

[38] . Phys. Lett. B, 665, 412-417(2008).

[39] . Phys. Lett. A, 286, 391-394(2001).

[40] . Phys. Rev. Lett., 87, 141601(2001).

[41] . JHEP, 0012, 002(2000).

[42] . Rev. Mod. Phys., 73, 977-1029(2001).

[43] . New J. Phys., 4, 57(2002).

[44] . Int. J. Mod. Phys. D, 11, 35-60(2002).

[45] . Phys. Rev. Lett., 103, 171302(2009).

[46] . Mod. Phys. Lett. A, 25, 3251-3266(2010).

[47] . Class. Quant. Grav., 27, 215003(2010).

[48] . Living Rev. Rel., 16, 5(2013).

[49] . EPL, 109, 50003(2015).

[50] . Phys. Lett. B, 718, 214-217(2012).

[51] . Int. J. Mod. Phys. D, 19, 2385-2392(2010).

[52] . EPL, 90, 30006(2010).

[53] . Mod. Phys. Lett. A, 27, 1250181(2012).

[54] . EPL, 91, 51002(2010).

[55] . Eur. Phys. J. C, 77, 666(2017).

[56] . JCAP, 0808, 027(2008).

[57] . Phys. Rev. A, 94, 013607(2016).

[58] . Phys. Rev. Lett., 101, 221301(2008).

[59] . Phys. Rev. D, 84, 044013(2011).

[60] . Phys. Rev. A, 81, 012106(2010).

[61] . Phys. Rev. Lett., 107, 203001(2011).

[62] . Phys. Rev. Lett., 110, 230801(2013).

[63] . Phys. Rev. D, 80, 116005(2009).

[64] . Nature Phys., 3, 87-90(2007).

[65] . Phys. Rev. Lett., 83, 2108-2111(1999).

[66] . JCAP, 1103, 046(2011).

[67] . Astropart. Phys., 20, 669-682(2004).

[68]

[69] . Phys. Rev. D, 66, 124006(2002).

[70] . Phys. Lett. B, 499, 1-8(2001).

[71] . JHEP, 0312, 013(2003).

[72] . Lect. Notes Phys., 541, 1-49(2000).

[73] . Phys. Rev. Lett., 96, 231601(2006).

[74] . Phys. Rev. A, 73, 032504(2006).

[75] . Phys. Rev. Lett., 100, 120801(2008).

[76] . Eur. Phys. J. Spec. Top., 172, 109-119(2009).

[77] . Phys. Rev. Lett., 92, 230802(2004).

[78] . Phys. Rev. D, 81, 041701(2010).

[79] . Atom. Data Nucl. Data Tabl., 33, 405-446(1985).

[80] . J. Phys. Chem. Ref. Data, 6, 831-870(1977).

[81] . J. Phys. B Atom. Mole. Optical Phys., 29, 177-195(1996).

[82] . Phys. Rev., 72, 339-341(1947).

[83] . Phys. Rev., 72, 241-243(1947).

[84] . Phys. Rev., 74, 1157-1167(1948).

[85] . J. Phys. Chem. Ref. Data, 45, 043102(2016).

[86] . Astron. Astrophys, 402, 409-424(2003).

[87] . JCAP, 0605, 017(2006).

[88] . Astrophys. J., 611, L77-L80(2004).

[89] . Astron. Astrophys., 345, L32-L34(1999).

[90] . Astrophys. J., 808, 78(2015).

[91] . Phys. Rev. Lett., 116, 151101(2016).

[92] . JCAP, 1608, 031(2016).

[93] . Commun. Phys., 1(2018).