Unresolved issues in galaxy formation theory

One of the greatest puzzles in galaxy formation theory concerns the distribution of the dark matter. The cold dark matter concentration is predicted from N-body simulations to follow a density profile  

rs is a scale factor that is incorporated into the concentration parameter, c = rn/rs. where rv is either the virial radius or the radius at an overdensity, spherically-averaged, of 200. The profile slope parameter 7 is measured in high resolution N-body simulations (,) to be 7 1.2 0.3, and the normalisation parameter A reflects the epoch of formation, typically defined to be when half of the present mass was at overdensity of 200. 

Unfortunately, observations seem to be in mild disagreement with this predicted profile merr. A low CDM concentration is observed in low surface brightness dwarf galaxies where the rotation curve is well measured. The predicted dark matter cusp is not usually seen the typical profile has a soft core, although the interpretation is compounded by issues of disk inclination, of the HI distribution which is usually used to measure the rotation curve, and of the possible mismatch between baryon and CDM potential well depths. 

The case for any discrepancy is weakened by the claim that the high resolution numerical simulations extrapolate to a core rasther than to a cusp. This result however is disputed by other simulators who find a central slope 7 = 0.16 0.14 that holds to 0.3% of the virial radius. In the Milky Way, a low concentration of nonbaryonic dark matter is inferred, with the argument 

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