 Tensor CMB line-of-sight source

Ignoring the last-scattering angular source and later scattering, the tensor-induced temperature anisotropy is $\Theta =-\frac{1}{2}{\int }_{{\eta }_{\ast }}^{{\eta }_0}{\dot{h}}_{ij}(\eta ,{\mathbf{x}}_0-({\eta }_0-\eta )\mathbf{e})e^i{e}^{j}d\eta$. An instantaneous cosmological visibility function alone leaves a scattering source at last scattering; leading tensor tight coupling supplies the additional reason to neglect it.