Distinguishing between cold dark matter and modified Newtonian dynamics: Predictions for the microwave background

Two hypothesized solutions for the mass discrepancy problem are cold dark matter and modified Newtonian dynamics. The virtues and vices of these very different hypotheses are largely disjointed, making the process of distinguishing between them very dependent on how we weigh disparate lines of evidence. One clear difference is the nature of the principal mass constituent of the universe (cold dark matter or baryons). This difference in the baryon fraction (f(b) approximate to 0.1 vs. 1) should leave a distinctive signature in the spectrum of fluctuations in the cosmic microwave background. Here I discuss some of the signatures that should be detectable in the near future. The most promising appears to be the ratio of the amplitudes of the first two peaks relative to the intervening trough.