Spectral distortions from the dissipation of tensor perturbations
Acoustic waves generate CMB spectral distortions because the linear superposition of blackbodies seen by electrons as they rescatter CMB photons is not itself a blackbody (see right panel of above figure). Gravitational waves similarly produce CMB spectral distortions due to the induced quadrupole seen by electrons at the surface of last scattering (see left panel of above figure). With Jens Chluba, Liang Dai, Mustafa Amin, and Marc Kamionkowski, we computed the CMB spectral distortion resulting from a stochastic background of gravitational waves as a function of their spectral index. For very blue spectral indices, these spectral distortions are detectably large, as we can see in the figure below.
Results published in arXiv: 1407.3653 (MNRAS 446 (3): 2871-2886)
Collaborators: Jens Chluba, Liang Dai, Mustafa Amin, Marc Kamionkowski.