** Next:** Compression and Vorticity
** Up:** CMB ANISOTROPIES: TOTAL ANGULAR
** Previous:** Integral Solutions

Before recombination, Thomson scattering between the photons and
electrons and coulomb interactions between the electrons and
baryons were sufficiently rapid that the photon-baryon system
behaves as a single tightly coupled fluid. Formally, one
expands the evolution equations in powers of the
Thomson mean free path over the wavelength and horizon
scale.
Here we briefly review well known results for the scalars (see e.g.
[25,26]) to show how vector or vorticity perturbations
differ in their behavior (§IVA).
In particular, the lack of
pressure support for the vorticity changes the relation between
the CMB and metric fluctuations.
We then study the higher order effects of
shear viscosity and polarization generation
from scalar, vector and tensor perturbations (§IVB).
We identify signatures in the temperature-polarization power spectra
that can help separate the types of perturbations.
Entropy generation and heat
conduction only occur for the scalars (§IVC)
and leads to differences in the dissipation rate for
fluctuations (§IVD).

*Wayne Hu*

*9/9/1997*