8 FIG. 1: (Colour Online) The snapshots of the distribution of particles. The 4 columns are for the 4 models we consider and the 3 rows are for three output times, respectively a = 0 . 2 , 0 . 5 and 1 (corresponding to redshifts 4, 1 and 0) where a is the cosmic scale factor. The red crosses denote baryons while blue dots represent CDM particles. All particles are take from a slice of the simulation box with 32 . 0 h − 1 Mpc < z < 32 . 1 h − 1 Mpc and projected to an $^{x}$− y plane. particles differ from each other. We see that for the model γ = 1 . 0 , µ = 10 − 5 the CDM particles could be up to ∼ 1 . 6 times faster than baryons, thanks to the enhancement by the fifth force. We will come back to this point later when we argue for the necessity of a modified strategy of identifying virialized halos. TABLE I: The mean velocity of all particles (¯ v ), baryons (¯ v B ) and CDM particles (¯ v CDM ) at z = 0 for the 20 coupled scalar field runs. The unit is proper km/s. parameters run no. ¯ v ¯ v$_{B}$ ¯ v$_{CDM}$ 1 367.68 337.71 375.18 2 367.70 337.69 375.19 γ = 0 . 5 , µ = 10 − 6 3 367.75 337.63 375.28 4 367.67 337.76 375.15 5 367.65 337.59 375.16 1 382.12 335.91 393.68 2 382.01 335.79 393.55 γ = 1 . 0 , µ = 10 − 6 3 381.91 335.79 393.55 4 382.01 335.87 393.54 5 382.05 335.83 393.61 1 412.75 357.36 426.60 2 412.75 357.49 426.55 γ = 0 . 5 , µ = 10 − 5 3 426.60 357.44 438.03 4 412.92 357.62 426.75 5 412.73 357.44 426.56 1 565.22 388.77 609.35 2 565.13 388.68 609.19 γ = 1 . 0 , µ = 10 − 5 3 565.19 388.82 609.30 4 565.58 388.25 609.66 5 564.64 388.75 608.63