  We obtain cosmological constraints from a measurement of the spherically
averaged power spectrum (PS) of the distribution of about 90000 luminous red
galaxies (LRGs) across 7646 deg2 in the Northern Galactic Cap from the DR7 of
the SDSS. The errors and mode correlations are estimated thanks to the 160
LasDamas mock catalogues, created in order to simulate the same galaxies and to
have the same selection as the data. We apply a model, that can accurately
describe the full shape of the PS with the use of a small number of free
parameters. Using the LRG PS, in combination with the latest measurement of the
temperature and polarisation anisotropy in the cosmic microwave background
(CMB), the luminosity-distance relation from the largest available type 1a
supernovae (SNIa) dataset and a precise determination of the local Hubble
parameter, we obtain cosmological constraints for five different parameter
spaces. When all the four experiments are combined, the flat LCDM model is
characterised by Omega_M=0.259+-0.016, Omega_b=0.045+-0.001, n_s=0.963+-0.011,
sigma_8=0.802+-0.021 and h=0.712+-0.014. When we consider curvature as a free
parameter, we do not detect deviations from flatness:
Omega_k=(1.6+-5.4)*10^{-3}, when only CMB and the LRG PS are used; the
inclusion of the other two experiments do not improve this result. Considering
the dark energy equation of state w_DE as time independent, we measure
w_DE=-1.025+-0.065, for a flat geometry, w_DE=-0.981+-0.083 otherwise. When
describing w_DE through a linear function of the scale factor, our results do
not evidence any time evolution. In the next few years new experiments will
allow to measure the clustering of galaxies with a precision much higher than
achievable today. Models like the one used here will be a valuable tool in
order to achieve the full potentials of the observations and obtain unbiased
constraints on the cosmological parameters.
