Vector cosmological perturbation
= Vector cosmological perturbation
A vector cosmological perturbation is the transverse-vector sector of linear metric and matter perturbations. For a <Fourier mode> with nonzero wavevector $\mathbf k$, transversality removes the component parallel to $\mathbf k$, leaving two <helicity> components. In a gauge with $ds^2=a^2[-d\eta^2+2B_i d\eta dx^i+\delta_{ij}dx^i dx^j]$, $\partial_iB_i=0$ describes the vector metric perturbation.