| Description |
With the success of Planck experiment we have extracted almost all information in the primary temperature anisotropies of CMB. Since Silk damping erases almost all primary perturbations on scales smaller than the Planck/SPT/ACT resolution, it is not possible to make significant progress by further improvement in resolution and we must look elsewhere as far as the initial conditions of the Universe are concerned. The information erased by Silk damping from the anisotropies ends up as spectral deviations from a blackbody in the CMB spectrum. CMB spectral deviations (mu-type and i-type) can thus gives us new information about the primordial power spectrum on very small scales (ℓ ∼ 105-108, corresponding to conventional anisotropy experiment with angular resolution of 6 milli-arcsec) which cannot be measured directly. In terms of inflation or initial conditions, these measurements will increase our view of inflation from 7 e-folds accessible at present from the observations of CMB anisotropies and large-scale structure to more than 17 e-folds. I will briefly review the physics behind the spectral features and discuss what information can be gained about the primordial initial conditions from their measurement with experiments such as Pixie and PRISM. I will also give a brief overview of the 4th generation CMB space mission PRISM currently being proposed to the European Space Agency.
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