Are Isocurvature Fluctuations of the M-theory Axion Observable?

Banks and Dine have recently shown that the M theory naturally accommodates the Peccei-Quinn axion. Since the decay constant $F_a$ of the axion is large as $F_a\simeq {10}^{15}-{10}^{16}$GeV, the halo axion is hardly detected in coming axion-search experiments. However, we show that isocurvature fluctuations of the M-theory axion produced at the inflationary epoch are most likely detectable in future satellite experiments on anisotropies of the cosmic microwave background radiation.