Observationally determining the properties of dark matter


Hu W, Eisenstein DJ, Tegmark M, White M. Observationally determining the properties of dark matter. Physical Review D. 1999;59 :23512.

Date Published:

August 1, 1999


Determining the properties of the dark components of the universeremains one of the outstanding challenges in cosmology. We explore howupcoming CMB anisotropy measurements, galaxy power spectrum data, andsupernova (SN) distance measurements can observationally constrain theirgravitational properties with minimal assumptions on the theoreticalside. SN observations currently suggest the existence of dark matterwith an exotic equation of state p/ρ<~-1/3 that accelerates theexpansion of the universe. When combined with CMB anisotropymeasurements, SN or galaxy survey data can in principle determine theequation of state and density of this component separately, regardlessof their value, as long as the universe is spatially flat. Combiningthese pairs creates a sharp consistency check. If p/ρ>~-1/2, thenthe clustering behavior (sound speed) of the dark component can bedetermined so as to test the scalar-field ``quintessence'' hypothesis.If the exotic matter turns out instead to be simply a cosmologicalconstant (p/ρ=-1), the combination of CMB and galaxy survey datashould provide a significant detection of the remaining dark matter, theneutrino background radiation (NBR). The gross effect of its density ortemperature on the expansion rate is ill constrained as it can bemimicked by a change in the matter density. However, anisotropies of theNBR break this degeneracy and should be detectable by upcomingexperiments.