  We investigate the consequences of a non-negligible baryon fraction for
models of structure formation in Cold Dark Matter dominated cosmologies,
emphasizing in particular the existence of oscillations in the present-day
matter power spectrum. These oscillations are the remnants of acoustic
oscillations in the photon-baryon fluid before last scattering. For acceptable
values of the cosmological and baryon densities, the oscillations modulate the
power by up to 10%, with a `period' in spatial wavenumber which is close to
Delta k approximately 0.05/ Mpc. We study the effects of nonlinear evolution on
these features, and show that they are erased for k > 0.2 h/ Mpc. At larger
scales, the features evolve as expected from second-order perturbation theory:
the visibility of the oscillations is affected only weakly by nonlinear
evolution. No realistic CDM parameter combination is able to account for the
claimed feature near k = 0.1 h/ Mpc in the APM power spectrum, or the excess
power at 100 Mpc/h wavelengths quoted by several recent surveys. Thus baryonic
oscillations are not predicted to dominate existing measurements of clustering.
We examine several effects which may mask the features which are predicted, and
conclude that future galaxy surveys may be able to detect the oscillatory
features in the power spectrum provided baryons comprise more than 15% of the
total density, but that it will be a technically challenging achievement.
