Bullet Clusters in the MareNostrum Universe
  We estimate the expected distribution of displacements between the dark
matter and gas cores in simulated clusters. We use the MareNostrum Universe,
one of the largest non radiative, SPH Lambda CDM cosmological simulations. We
find that projected 2-D displacements between dark matter and gas, equal or
larger than the observed in the Bullet Cluster, are expected in 1% to 2% of the
clusters with masses larger than 10^{14} Msun. The 2-D displacement
distribution is roughly the same between redshifts 0<z<0.5 when multiplied by a
factor of (1+z)^{-1/2}. We conclude that the separations between dark matter
and gas as observed in the bullet cluster can be easily found in a Lambda CDM
universe. Furthermore we find that the displacement distribution is not very
sensitive to the normalization of the power spectrum. Upcoming surveys could
extend the measurements of these displacements between dark matter and gas into
large samples of hundreds of clusters, providing a potential test for Lambda
CDM.
