Constraining the growth rate by combining multiple future surveys
  The growth rate of large-scale structure provides a powerful consistency test
of the standard cosmological model and a probe of possible deviations from
general relativity. We use a Fisher analysis to forecast constraints on the
growth rate from a combination of next-generation spectroscopic surveys. In the
overlap survey volumes, we use a multi-tracer analysis to significantly reduce
the effect of cosmic variance. The non-overlap individual survey volumes are
included in the Fisher analysis in order to utilise the entire volume. We use
the observed angular power spectrum, which naturally includes all wide-angle
and lensing effects and circumvents the need for an Alcock-Paczynski
correction. Cross correlations between redshift bins are included by using a
novel technique to avoid computation of the sub-dominant contributions.
Marginalising over the standard cosmological parameters, as well as the
clustering bias in each redshift bin, we find that the precision on $\gamma$
improves on the best single-tracer precision by up to $\sim$50\%.
