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Nominated as an outstanding thesis by Professor Robert Crittenden
of the Institute of Cosmology and Gravitation in Portsmouth, and
winner of the Michael Penston Prize for 2014 given by the Royal
Astronomical Society for the best doctoral thesis in Astronomy or
Astrophysics, this work aims to shed light on one of the most
important probes of the early Universe: the bispectrum of the
cosmic microwave background. The CMB bispectrum is a potential
window on exciting new physics, as it is sensitive to the
non-Gaussian features in the primordial fluctuations, the same
fluctuations that evolved into today's planets, stars and galaxies.
However, this invaluable information is potentially screened, as
not all of the observed non-Gaussianity is of primordial origin.
Indeed, a bispectrum arises even for perfectly Gaussian initial
conditions due to non-linear dynamics, such as CMB photons
scattering off free electrons and propagating in an inhomogeneous
Universe. Dr. Pettinari introduces the reader to this intrinsic
bispectrum in a pedagogic way, building up from the standard model
of cosmology and from cosmological perturbation theory, the tool
cosmologists use to unravel the history of the cosmos. In doing so,
he introduces SONG, a new and efficient code for solving the
second-order Einstein and Boltzmann equations. Next, he moves on to
answer the crucial question: is the intrinsic bispectrum going to
screen the primordial signal in the CMB? Using SONG, he computes
the intrinsic bispectrum and shows how its contamination leads to a
small bias in the estimates of primordial non-Gaussianity, a great
news for the prospect of using CMB data to probe primordial
non-Gaussianity.
Nominated as an outstanding thesis by Professor Robert Crittenden
of the Institute of Cosmology and Gravitation in Portsmouth, and
winner of the Michael Penston Prize for 2014 given by the Royal
Astronomical Society for the best doctoral thesis in Astronomy or
Astrophysics, this work aims to shed light on one of the most
important probes of the early Universe: the bispectrum of the
cosmic microwave background. The CMB bispectrum is a potential
window on exciting new physics, as it is sensitive to the
non-Gaussian features in the primordial fluctuations, the same
fluctuations that evolved into today's planets, stars and galaxies.
However, this invaluable information is potentially screened, as
not all of the observed non-Gaussianity is of primordial origin.
Indeed, a bispectrum arises even for perfectly Gaussian initial
conditions due to non-linear dynamics, such as CMB photons
scattering off free electrons and propagating in an inhomogeneous
Universe. Dr. Pettinari introduces the reader to this intrinsic
bispectrum in a pedagogic way, building up from the standard model
of cosmology and from cosmological perturbation theory, the tool
cosmologists use to unravel the history of the cosmos. In doing so,
he introduces SONG, a new and efficient code for solving the
second-order Einstein and Boltzmann equations. Next, he moves on to
answer the crucial question: is the intrinsic bispectrum going to
screen the primordial signal in the CMB? Using SONG, he computes
the intrinsic bispectrum and shows how its contamination leads to a
small bias in the estimates of primordial non-Gaussianity, a great
news for the prospect of using CMB data to probe primordial
non-Gaussianity.
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