Dark Matter

Abstract

europhysics news NOVEMBER/DECEMBER 2001 Fig. 1: Mean matter/energy density in the universe normalised to the critical density. Avalue of Q=1means a flat universe topology as the bounctary case between a spherical and hyperbolic topology (for .simple cosmologies this means closed and open universe). Summaries of measurements for this important parameter are indicated. Below the logarithmic axis is shown an overall account of matter and energy; above the compOSition ofthe matter components.The dotted red rectangles,labeled gap I and 11 indicate the two dark matter problems: dark baryons and non-baryonic dark matter. Colored regions: yellow range of luminous matter, brown required range of baryonic matter due to primordial nucleosynthesis, light green range of non-baryonic cold dark matter (CDM), red total account of matter/energy density consistent with Q=1, dark green total matter content in the universe, blue ~ dark energy content adding up with matter to the total content. The dashed green rectangle shows the allowed amount of matter density due to neutrinos. Lower bound due to successful neutrino mass measurements, upper bound from failure of structure formation scenarios using neutrinos as hot dark matter.The picture has been adopted from M.5.Turner's dark matter review in Phys. Reports (see references). Malb% composition