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Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 02/05 Podcast
Cosmic sound: Measuring the Universe with baryonic acoustic oscillations

Cosmic sound: Measuring the Universe with baryonic acoustic oscillations

Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 02/05 vor 20 Jahren

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During the last ten to fifteen years cosmology has turned from a
data-starved to a data-driven science. Several key parameters of
the Universe have now been measured with an accuracy better than
10%. Surprisingly, it has been found that instead of slowing down,
the expansion of the Universe proceeds at an ever increasing rate.
From this we infer the existence of a negative pressure component
-- the so-called Dark Energy (DE) -- that makes up more than two
thirds of the total matter-energy content of our Universe. It is
generally agreed amongst cosmologists and high energy physicists
that understanding the nature of the DE poses one of the biggest
challenges for the modern theoretical physics. Future cosmological
datasets, being superior in both quantity and quality to currently
existing data, hold the promise for unveiling many of the
properties of the mysterious DE component. With ever larger
datasets, as the statistical errors decrease, one needs to have a
very good control over the possible systematic uncertainties. To
make progress, one has to concentrate the observational effort
towards the phenomena that are theoretically best understood and
also least ``contaminated'' by complex astrophysical processes or
several intervening foregrounds. Currently by far the cleanest
cosmological information has been obtained through measurements of
the angular temperature fluctuations of the Cosmic Microwave
Background (CMB). The typical angular size of the CMB temperature
fluctuations is determined by the distance the sound waves in the
tightly coupled baryon-photon fluid can have traveled since the Big
Bang until the epoch of recombination. A similar scale is also
expected to be imprinted in the large-scale matter distribution as
traced by, for instance, galaxies or galaxy clusters. Measurements
of the peaks in the CMB angular power spectrum fix the physical
scale of the sound horizon with a high precision. By identifying
the corresponding features in the low redshift matter power
spectrum one is able to put constraints on several cosmological
parameters. In this thesis we have investigated the prospects for
the future wide-field SZ cluster surveys to detect the acoustic
scale in the matter power spectrum, specifically concentrating on
the possibilities for constraining the properties of the DE. The
core part of the thesis is concerned with a power spectrum analysis
of the SDSS Luminous Red Galaxy (LRG) sample. We have been able to
detect acoustic features in the redshift-space power spectrum of
LRGs down to scales of ~ 0.2 hMpc^{-1}, which approximately
corresponds to the seventh peak in the CMB angular spectrum. Using
this power spectrum measurement along with the measured size of the
sound horizon, we have carried out the maximum likelihood
cosmological parameter estimation using Markov chain Monte Carlo
techniques. The precise measurement of the low redshift sound
horizon in combination with the CMB data has enabled us to measure,
under some simplifying assumptions, the Hubble constant with a high
precision: H_0 = 70.8 {+1.9} {-1.8} km/s/Mpc. Also we have shown
that a decelerating expansion of the Universe is ruled out at more
than 5-sigma confidence level.