2012ApJ...747...45L

It has been recently shown that the observed morphological properties of the Bullet Cluster can be accurately reproduced in hydrodynamical simulations only when the infall pairwise velocity V_c of the system exceeds 3000 km/s (or at least possibly 2500 km/s) at the pair separation of 2R_vir, where R_vir is the virial radius of the main cluster, and that the probability of finding such a bullet-like system is extremely low in the standard Λ cold dark matter (ΛCDM) cosmology. We suggest here the fifth force mediated by coupled dark energy (cDE) as a possible velocity-enhancing mechanism and investigate its effect on the infall velocities of bullet-like systems from the Coupled Dark Energy Cosmological Simulations public database. Five different cDE models are considered: three with constant coupling and exponential potential, one with exponential coupling and exponential potential, and one with constant coupling and supergravity potential. For each model, after identifying the bullet-like systems, we determine the probability density distribution of their infall velocities at pair separations of (2-3)R_vir. Approximating each probability density distribution as a Gaussian, we calculate the cumulative probability of finding a bullet-like system with V_c ≥ 3000 km/s or V_c ≥ 2500 km/s. Our results show that in all of the five cDE models the cumulative probabilities increase compared to the ΛCDM case and that in the model with exponential coupling P(V_c ≥ 2500 km/s) exceeds 10^–4. The physical interpretations and cosmological implications of our results are provided.