  Near-future facilities observing the high-redshift universe ($2<z<5$) will
have an opportunity to take advantage of "multi-tracer" cosmology by observing
multiple tracers of the matter density field: Lyman alpha emitters (LAE), Lyman
break galaxies (LBG), and CMB lensing $\kappa$. In this work we use Fisher
forecasts to investigate the effect of multi-tracers on next-generation
facilities. In agreement with previous work, we show that multiple tracers
improve constraints primarily from degeneracy breaking, instead of the
traditional intuition of sample variance cancellation. Then, we forecast that
for both BBN and CMB primary priors, the addition of lensing and LAEs onto a
LBG-only sample will gain 25\% or more in many parameters, with the largest
gains being factor of $\sim10$ improvement for $f_{\rm EDE}$. We include a
preliminary approach towards modelling the impact of radiative transfer (RT) on
forecasts involving LAEs by introducing a simplified model at linear theory
level. Our results, albeit preliminary, show that the while RT influences
LAE-only forecasts strongly, its effect on composite multi-tracer forecasts are
limited.
