  We employ gauge-gravity duality to study the backreaction effect of
4-dimensional large-$N$ quantum field theories on constant-curvature
backgrounds, and in particular de Sitter space-time. The field theories
considered are holographic QFTs, dual to RG flows between UV and IR CFTs. We
compute the holographic QFT contribution to the gravitational effective action
for 4d Einstein manifold backgrounds. We find that for a given value of the
cosmological constant $\lambda$, there generically exist two backreacted
constant-curvature solutions, as long as $\lambda < \lambda_{\textrm{max}} \sim
M_p^2 / N^2$, otherwise no such solutions exist. Moreover, the backreaction
effect interpolates between that of the UV and IR CFTs. We also find that, at
finite cutoff, a holographic theory always reduces the bare cosmological
constant, and this is the consequence of thermodynamic properties of the
partition function of holographic QFTs on de Sitter.
