We present results from the analysis of cosmic microwave background ( CMB ) , large scale structure ( galaxy redshift survey ) and X-ray galaxy cluster ( baryon fraction and X-ray luminosity function ) data , assuming a geometrically flat cosmological model and allowing for tensor components and a non-negligible neutrino mass .
From a combined analysis of all data , assuming three degenerate neutrinos species , we measure a contribution of neutrinos to the energy density of the universe , \Omega _ { \nu } h ^ { 2 } = 0.0059 ^ { +0.0033 } _ { -0.0027 } ( 68 per cent confidence limits ) , with zero falling on the 99 per cent confidence limit .
This corresponds to \sim 4 per cent of the total mass density of the Universe and implies a species-summed neutrino mass \sum _ { i } m _ { i } = 0.56 ^ { +0.30 } _ { -0.26 } eV , or m _ { \nu } \sim 0.2 eV per neutrino .
We examine possible sources of systematic uncertainty in the results .
Combining the CMB , large scale structure and cluster baryon fraction data , we measure an amplitude of mass fluctuations on 8 h ^ { -1 } Mpc scales of \sigma _ { 8 } = 0.74 ^ { +0.12 } _ { -0.07 } , which is consistent with measurements based on the X-ray luminosity function and other studies of the number density and evolution of galaxy clusters .
This value is lower than that obtained when fixing a negligible neutrino mass ( \sigma _ { 8 } = 0.86 ^ { +0.08 } _ { -0.07 } ) .
The combination of CMB , large scale structure and cluster baryon fraction data also leads to remarkably tight constraints on the Hubble constant , H _ { 0 } = 68.4 ^ { +2.0 } _ { -1.4 } \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } { \thinspace Mpc } ^ { -1 } , mean matter density , \Omega _ { m } = 0.31 \pm 0.02 and physical baryon density , \Omega _ { b } h ^ { 2 } = 0.024 \pm 0.001 , of the Universe .