Microwave background anisotropies from Alfven waves - art. no. 123004

We investigate microwave background anisotropies in the presence of primord ial magnetic fields. We show that a homogeneous field with fixed direction can amplify vector perturbations. We calculate the correlations of delta T/ T explicitly and show that a large scale coherent field induces correlation s between a(l-1,m) and a(l+1,m). We discuss constraints on the amplitude an d spectrum of a primordial magnetic held imposed by observations of CMB ani sotropies. [S0556-2821(98)06224-9].