  The clustering ratio is defined as the ratio between the correlation function
and the variance of the smoothed overdensity field. In LCDM cosmologies not
accounting for massive neutrinos, it has already been proved to be independent
from bias and redshift space distortions on a range of linear scales. It
therefore allows for a direct comparison of measurements (from galaxies in
redshift space) to predictions (for matter in real space). In this paper we
first extend the applicability of such properties of the clustering ratio to
cosmologies that include massive neutrinos, by performing tests against
simulated data. We then investigate the constraining power of the clustering
ratio when cosmological parameters such as the total neutrino mass and the
equation of state of dark energy are left free. We analyse the joint posterior
distribution of the parameters that must satisfy, at the same time, the
measurements of the galaxy clustering ratio in the SDSS DR12, and the angular
power spectrum of temperature and polarization anisotropies of the CMB measured
by the Planck satellite. We find the clustering ratio to be very sensitive to
the CDM density parameter, but not very much so to the total neutrino mass.
Lastly, we forecast the constraining power the clustering ratio will achieve
with forthcoming surveys, predicting the amplitude of its errors in a
Euclid-like galaxy survey. In this case, we find it is expected to improve the
constraint at 95% level on the CDM density by 40% and on the total neutrino
mass by 14%.
