http://arxiv.org/abs/1405.2280
[Abridged version] A huge theoretical and experimental effort is being made by cosmologists and particle physicists to gain insight of the mechanism of generation of the primordial cosmological fluctuations, which remains still largely unknown. The bispectrum of the cosmic microwave background (CMB) has been recognised as a powerful probe of this mechanism, as it is sensitive to the non-Gaussian features in the seed fluctuations. To access this information, however, it is crucial to model the non-linear evolution of the CMB between the formation of the initial fluctuations and its observation, which results in the emergence of an intrinsic bispectrum. In this thesis we quantify the intrinsic bispectrum and compute the bias it induces on the primordial signal. To do so, we develop $\text{SONG}$, an efficient code for solving the second-order Einstein-Boltzmann equations, and use it to estimate the CMB non-Gaussianity arising from the non-linear evolution of density perturbations. The full calculation involves contributions from recombination and less tractable ones from terms integrated along the line of sight. We investigate the bias that the intrinsic bispectrum implies for searches of primordial non-Gaussianity. We find that the inclusion or omission of certain line of sight terms can make a large impact. When including all physical effects but lensing and time-delay, we find that the contamination from the intrinsic bispectrum leads to a small bias in the estimates of non-Gaussianity, which is good news for the prospect of using CMB data to probe primordial non-Gaussianity. The intrinsic non-Gaussianity can be searched for directly, using the predicted signal as a template; our calculations suggest this signal is just beyond what is possible with the Planck CMB survey, with a signal-to-noise rising to unity only for an angular resolution of $\ell_\text{max}=3000$.
G. Pettinari
Mon, 12 May 14
7/40
Comments: This is my Ph.D. thesis. It is long (250 pages) as I have striven to make it understandable by a Ph.D. student. Feel free to contact me or visit this http URL for information or a printable version. Note that new results (Pettinari et al. 2104 to be submitted soon) suggest that the intrinsic bispectrum has a much larger S/N when also polarisation is included
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