Primordial Vector Modes
Primordial vector modes are discussed in my paper astro-ph/0403583.
Some derivations are available in Maple 6 format (note other versions may not work):
Interestingly there is actually a small correction to the O(eta) sigma series result when tight coupling is not assumed,
The regular vector mode is now supported by CAMB. Further details of the vector modes theory are given in astro-ph/0406096.
Antony Lewis March 04