18 FIG. 10: Distribution of the velocities of the particles in halo I and the fifth-force-to-gravity ratio at the positions of these particles, for the two models γ = 0 . 5 , µ = 10 − 5 and γ = 1 . 0 , µ = 10 − $^{5}$. Each dots represent a particle. UK National Cosmology Supercomputer. We thank John Barrow, Kazuya Koyama, Andrea Maccio and Gong-Bo Zhao for helpful discussions relevant to this work, and Lin Jia for assistance in plotting the figures. B. Li is sup- ported by a Research Fellowship in Applied Mathemat- ics at Queens’ College, University of Cambridge and the STFC rolling grant in DAMTP. The work described here has been performed under the HPC-EUROPA project, with the support of the Eu- ropean Community Research Infrastructure Action un- der the FP8 ”Structuring the European Research Area” Programme. The N -body simulations are performed on the Huygens supercomputer in the Netherlands, and the post-precessing of data is performed on COSMOS, the Acknowledgments [11] B. Li and J. D. Barrow, Phys. Rev. D 75 , 084010 (2007). [12] W. Hu and I. Sawicki, Phys. Rev. D 76 , 064004 (2007). [13] P. Brax, C. van de Bruck, A. -C. Davis and D. J. Shaw, Phys. Rev. D 78 , 104021 (2008). [14] E. Bertschinger, Ann. Rev. Astron. Astrophys. 36 , 599 (1998). [15] E. V. Linder and A. Jenkins, Mon. Not. R. Astron. Soc. 346 , 573 (2003). [16] R. Mainini, A. V. Maccio, S. A. Bonometto and A. Klypin, Astrophys. J. 599 , 24 (2003). [17] V. Springel and G. R. Farrar, Mon. Not. R. Astron. Soc. 380 , 911 (2007). [18] M. Kesden and M. Kamionkowski, Phys. Rev. Lett. 97 , 131303 (2006); Phys. Rev. D 74 , 083007 (2006) [19] G. R. Farrar and R. A. Rosen, Phys. Rev. Lett. 98 , 171302 (2007). [20] J. A. Keselman, A. Nusser and P. J. E. Peebles (2007), arXiv:0902.3452 [astro-ph]. [1] E. J. Copeland, M. Sami and S. Tsujikawa, Int. J. Mod. Phys. D 15 , 1753 (2006). [3] J. Khoury and A. Weltman, Phys. Rev. Lett. 93 , 171104 (2004). [2] L. Amendola, Phys. Rev. D 62 , 043511 (2000). [4] J. Khoury and A. Weltman, Phys. Rev. D 69 , 044026 (2004). [5] D. F. Mota and D. J. Shaw, Phys. Rev. Lett. 97 , 151102 (2006). [6] D. F. Mota and D. J. Shaw, Phys. Rev. D 75 , 063501 (2007). [7] P. Brax, C. van de Bruck, A. -C. Davis, J. Khoury and A. Weltman, Phys. Rev. D 70 , 123518 (2004). [8] S. M. Carroll, V. Duvvuri, M. Trodden and M. S Turner, Phys. Rev. D 70 , 043528 (2004). [9] S. Nojiri and S. D. Odintsov, Phys. Rev. D 68 , 123512 (2003). [10] I. Navarro and K. van Acoleyen, JCAP 02 , 022 (2007).