The imprint of primordial gravitational waves on the CMB intensity profile

Understand

We use the induced geometry on the two dimensional transverse cross section of a photon beam propagating on a perturbed Friedmann-Robertson-Walker (FRW) spacetime to find the Cosmic Microwave Background (CMB) photon distribution over a telescope's collecting area today.

• It turns out that at each line of sight the photons are diluted along a transverse direction due to gravitational shearing.
• The effect can be characterized by two spin-weight-two variables, which are reminiscent of the Stokes polarization parameters.
• Similar to that case, one can construct a scalar and a pseudo-scalar function where the latter only gets contributions from the tensor modes.