Primordial magnetic fields present since before the epoch of matter-radiation
equality have an effect on the anisotropies of the cosmic microwave background.
The CMB anisotropies due to scalar perturbations are calculated in the gauge
invariant formalism for magnetized adiabatic initial conditions. Furthermore
the linear matter power spectrum is calculated. Numerical solutions are
complemented by a qualitative analysis.Comment: 26 pages, 21 figures; sections 2 and 4 expanded; matches version
published in PR