MG13 - Talk detail

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Mixing of blackbodies with different temperatures creates a spectral distortion which, at lowest order, is a y-type distortion, indistinguishable from the thermal y-type distortion we get from the scattering of CMB photons by hot electrons in clusters of galaxies. Such a mixing of blackbodies occurs in the early Universe as photons from different phases of the sound waves (excited by primordial perturbations) diffuse through the electron-baryon plasma and mix together. This diffusion, thus, dissipates the sound waves (Silk damping) and creates spectral distortions in CMB. Out of the total initial energy in the CMB temperature perturbations, 2/3 raises the average temperature of the blackbody part of spectrum and is not directly observable, while 1/3 creates entropy and an observable spectral distortion of y-type which subsequently comptonizes to a $\mu$ distortion at high redshifts (z>10^5). Observations of spectral distortions of CMB thus hold the promise to constrain and measure the primordial power spectrum at very small scales, comoving wavenumbers of 10<k<10^4 Mpc^{-1}.

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