We discuss the detectability of large-scale HI intensity fluctuations using
the FAST telescope. We present forecasts for the accuracy of measuring the
Baryonic Acoustic Oscillations and constraining the properties of dark energy.
The FAST 19-beam L-band receivers (1.05--1.45 GHz) can provide
constraints on the matter power spectrum and dark energy equation of state
parameters (w0​,wa​) that are comparable to the BINGO and CHIME
experiments. For one year of integration time we find that the optimal survey
area is 6000deg2. However, observing with larger frequency coverage
at higher redshift (0.95--1.35 GHz) improves the projected errorbars on the
HI power spectrum by more than 2 σ confidence level. The combined
constraints from FAST, CHIME, BINGO and Planck CMB observations can provide
reliable, stringent constraints on the dark energy equation of state.Comment: 7 pages, 3 figures, submitted to "Frontiers in Radio Astronomy and
FAST Early Sciences Symposium 2015" conference proceedin