  We discuss how the baryon acoustic oscillation (BAO) signatures in the galaxy
power spectrum can distinguish between modified gravity and the cosmological
constant as the source of cosmic acceleration. To this end we consider a model
characterized by a parameter $n$, which corresponds to the
Dvali-Gabadadze-Porrati (DGP) model if $n=2$ and reduces to the standard
spatially flat cosmological constant concordance model for $n$ equal to
infinity. We find that the different expansion histories of the modified
gravity models systematically shifts the peak positions of BAO. A preliminary
analysis using the current SDSS LRG sample indicates that the original DGP
model is disfavored unless the matter density parameter exceeds 0.3. The
constraints will be strongly tightened with future spectroscopic samples of
galaxies at high redshifts. We demonstrate that WFMOS, in collaboration with
other surveys such as Planck, will powerfully constrain modified gravity
alternatives to dark energy as the explanation of cosmic acceleration.
