Spectral distortions from the dissipation of tensor perturbations

Left panel shows the temperature pattern seen by an electron in the metric field of a passing gravitational wave. Right panel shows spectrum of superposition of blackbodies compared with a blackbody at their mean temperature, as well as chemical potential and y-type spectral distortions. Shown as a function of dimensionless frequency (normalized relative to the temperature).

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.