Degeneracy between n_s, Ω_bh², and foreground amplitudes in TT for the single CMB and foreground realization used in the E2E simulations. Horizontal and vertical dashed lines indicate the cosmological parameters obtained in the refTT case and the known foreground amplitudes of the simulation, while the red contours indicate the values obtained in the inputTT case. Upward shifts of up to 1.5 σ in foregrounds are associated with downward shifts in cosmological parameters of close to 1 σ and are due to chance correlations in the particular CMB and foreground realization that we are using for the simulations. This accounts for the shifts in foreground amplitudes found in Fig. 88.