  We study the asymmetry between the vector current and axial-vector current
correlators in the colour-flavour locking (CFL) phase of QCD at finite density.
Using Weinberg's sum rules, we compute the decay constant $f_\pi$ of the
Goldstone modes and find agreement with previous derivations. Using Das's sum
rule, we also estimate the contribution of electromagnetic interactions to the
mass of the charged modes. Finally, we comment on low temperature corrections
to the effective field theory describing the Goldstone bosons.
