Has cosmological dark matter been observed?
  There are many indications that ordinary matter represents only a tiny fraction of the matter content of the Universe, with the remainder assumed to consist of some different type of matter, which, for various reasons must be nonluminous (dark matter). Among these indications are the inflationary scenarios which predicts that the average energy density of the Universe coincides with the so called critical value (for which the expansion never stops but the rate of expansion approaches zero at very late times). At the same time it is known (from the predictions of Big Bang nucleosynthesis on the abundances of the light elements, other than Helium) that the baryonic energy density (ordinary matter) must represent ($1.5\pm 0.5)h^{-2}$ \% (where $h$ is the Hubble constant in units of 100 km s$^{-1}$Mpc$^{-1}$) of this critical value \cite{Copi,OstStein}. We present here evidence supporting the model in which the rest of the energy density corresponds to a scalar field, which can be observed, however indirectly, in the oscillation of the effective gravitational constant, and manifests itself in the known periodicity of the number distribution of galaxies \cite{Broad,Szalay}. We analyze this model numerically and show that, the requirement that the model satisfy the bounds of light element abundances in the Universe, as predicted by Big Bang nucleosynthesis, yields a specific value for the red-shift-galactic-count oscillation amplitude compatible with that required to explain the oscillations described above \cite{hill,CritStein}, and, furthermore, yields a value for the age of the Universe compatible with standard bounds \cite{OstStein}. 
Marcelo Salgado, Daniel Sudarsky, and Hernando Quevedo