Abstract
By detecting redshift drift in the spectra of the Lyman-α forest of distant quasars, the Sandage–Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of 2≲z≲5. Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of the SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (i) Q=γHρc, (ii) Q=γHρde, (iii) Q=γH0ρc, and (iv) Q=γH0ρde. The results show that for all the considered interacting dark energy models, relative to the current joint SN + BAO + CMB + H0 observations, the constraints on Ωm and H0 would be improved by about 60 and 30–40 %, while the constraints on w and γ would be slightly improved, with a 30-year observation of the SL test. We also explore the impact of the SL test on future joint geometric observations. In this analysis, we take the model with Q=γHρc as an example, and we simulate future SN and BAO data based on the space-based project WFIRST. We find that with the future geometric constraints, the redshift drift observations would help break the geometric degeneracies in a meaningful way, thus the measurement precisions of Ωm, H0, w, and γ could be substantially improved using future probes.