33 research outputs found
Cosmic sound: Measuring the Universe with baryonic acoustic oscillations
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
Acoustic oscillations in the SDSS DR4 Luminous Red Galaxy sample power spectrum
We calculate the redshift-space power spectrum of the Sloan Digital Sky
Survey (SDSS) Data Release 4 (DR4) Luminous Red Galaxy (LRG) sample, finding
evidence for a full series of acoustic features down to the scales of \sim 0.2
hMpc^{-1}. This corresponds up to the 7th peak in the CMB angular power
spectrum. The acoustic scale derived, (105.4 \pm 2.3) h^{-1}Mpc, agrees very
well with the ``concordance'' model prediction and also with the one determined
via the analysis of the spatial two-point correlation function by Eisenstein et
al. (2005). The models with baryonic features are favored by 3.3 \sigma over
their ``smoothed-out'' counterparts without any oscillatory behavior.Comment: Extended version of the previous work astro-ph/0507678, now including
new data from the SDSS DR4. 17 pages, 18 figures, accepted for publication in
A&
Combining clustering and abundances of galaxy clusters to test cosmology and primordial non-Gaussianity
We present the clustering of galaxy clusters as a useful addition to the
common set of cosmological observables. The clustering of clusters probes the
large-scale structure of the Universe, extending galaxy clustering analysis to
the high-peak, high-bias regime. Clustering of galaxy clusters complements the
traditional cluster number counts and observable-mass relation analyses,
significantly improving their constraining power by breaking existing
calibration degeneracies. We use the maxBCG galaxy clusters catalogue to
constrain cosmological parameters and cross-calibrate the mass-observable
relation, using cluster abundances in richness bins and weak-lensing mass
estimates. We then add the redshift-space power spectrum of the sample,
including an effective modelling of the weakly non-linear contribution and
allowing for an arbitrary photometric redshift smoothing. The inclusion of the
power spectrum data allows for an improved self-calibration of the scaling
relation. We find that the inclusion of the power spectrum typically brings a
per cent improvement in the errors on the fluctuation amplitude
and the matter density . Finally, we apply this
method to constrain models of the early universe through the amount of
primordial non-Gaussianity of the local type, using both the variation in the
halo mass function and the variation in the cluster bias. We find a constraint
on the amount of skewness () from the
cluster data alone.Comment: 12 pages, 10 figures, 2 tables. Minor changes to match published
version on MNRA
Testing general relativity with the multipole spectra of the SDSS luminous red galaxies
As a test of general relativity on cosmological scales, we measure the \gamma
parameter for the growth rate of density perturbations using the redshift-space
distortion of the luminous red galaxies in the Sloan Digital Sky Survey (SDSS).
Assuming the cosmological constant model, which matches the results of the WMAP
experiment, we find \gamma=0.62+1.8(\sigma_8-0.8) \pm 0.11 at 1-sigma
confidence level, which is consistent with the prediction of general
relativity, \gamma\simeq0.55\sim0.56. Rather high value of \sigma_8(\geq0.87)
is required to be consistent with the prediction of the cosmological DGP model,
\gamma\simeq0.68.Comment: important mistake in computation correcte
Minimal dark matter in type III seesaw
We explore the possibility of a new dark matter candidate in the
supersymmetric type III seesaw mechanism where a neutral scalar component of
the Y=0 triplet can be the lightest supersymmetric particle. Its thermal
abundance can be in the right range if non-standard cosmology such as kination
domination is assumed. The enhanced cross-section of the dark matter
annihilation to W+W- can leave detectable astrophysical and cosmological
signals whose current observational data puts a lower bound on the dark matter
mass. The model predicts the existence of a charged scalar almost degenerate
with the dark matter scalar and its lifetime lies between 5.5 cm and 6.3 m. It
provides a novel opportunity of the dark mater mass measurement by identifying
slowly-moving and highly-ionizing tracks in the LHC experiments. If the
ordinary lightest supersymmetric particle is the usual Bino, its decay leads to
clean signatures of same-sign di-lepton and di-charged-scalar associated with
observable displaced vertices which are essentially background-free and can be
fully reconstructed.Comment: 3 figures, 12 pages; An error in the antiproton limit corrected; the
lower bound on the dark matter mass strengthened; references added; typos
correcte
Enhanced anti-deuteron Dark Matter signal and the implications of PAMELA
We show that the jet structure of DM annihilation or decay products enhances
the anti-deuterium production rate by orders of magnitude compared to the
previous computations done assuming a spherically symmetric coalescence model.
In particular, in the limit of heavy DM, M >> m_p, we get a constant rather
than 1/M^2 suppressed anti-deuterium production rate. Therefore, a detectable
anti-deuterium signal is compatible with the lack of an excess in the
anti-proton PAMELA flux. Most importantly, cosmic anti-deuterium searches
become sensitive to the annihilations or decays of heavy DM, suggesting to
extend the experimental anti-deuterium searches above the O(1) GeV scale.Comment: 13 pages, 7 figures. Final versio