Modern Cosmology begins with an introduction to the smooth, homogeneous universe described by a Friedman-Robertson-Walker metric, including careful treatments of dark energy, big bang ...nucleosynthesis, recombination, and dark matter. From this starting point, the reader is introduced to perturbations about an FRW universe: their evolution with the Einstein-Boltzmann equations, their generation by primordial inflation, and their observational consequences. These consequences include the anisotropy spectrum of the cosmic microwave background (CMB) featuring acoustic peaks and polarization, the matter power spectrum with baryonic wiggles, and their detection via photometric galaxy surveys, redshift distortions, cluster abundances, and weak lensing. The book concludes with a long chapter on data analysis. Modern Cosmology is the first book to explain in detail the structure of the acoustic peaks in the CMB, the E/B decomposition in polarization which may allow for detection of primordial gravity waves, and the modern analysis techniques used on increasingly large cosmological data sets. Readers will gain the tools needed to work in cosmology and learn how modern observations are rapidly revolutionizing our picture of the universe. * Provides foundations, calculations, and interpretations which illuminate current thinking in cosmology * Covers the major advances in cosmology over the past decade * Includes over 100 unique, pedagogical figures.
The recent BICEP2 measurement of B modes in the polarization of the cosmic microwave background suggests that inflation was driven by a field at an energy scale of 2 × 10(16) GeV. I explore the ...potential of upcoming cosmic microwave radiation polarization experiments to further constrain the physics underlying inflation. If the signal is confirmed, then two sets of experiments covering a large area will shed light on inflation. Low-resolution measurements can pin down the tensor to scalar ratio at the percent level, thereby distinguishing models from one another. A high angular resolution experiment will be necessary to measure the tilt of the tensor spectrum, testing the consistency relation that relates the tilt to the amplitude.
The B-modes of polarization at frequencies ranging from 50–1000 GHz are produced by Galactic dust, lensing of primordial E-modes in the cosmic microwave background (CMB) by intervening large scale ...structure, and possibly by primordial B-modes in the CMB imprinted by gravitational waves produced during inflation. The conventional method used to separate the dust component of the signal is to assume that the signal at high frequencies (e.g. 350 GHz) is due solely to dust and then extrapolate the signal down to a lower frequency (e.g. 150 GHz) using the measured scaling of the polarized dust signal amplitude with frequency. For typical Galactic thermal dust temperatures of ∼20 K, these frequencies are not fully in the Rayleigh-Jeans limit. Therefore, deviations in the dust cloud temperatures from cloud to cloud will lead to different scaling factors for clouds of different temperatures. Hence, when multiple clouds of different temperatures and polarization angles contribute to the integrated line-of-sight polarization signal, the relative contribution of individual clouds to the integrated signal can change between frequencies. This can cause the integrated signal to be decorrelated in both amplitude and direction when extrapolating in frequency. Here we carry out a Monte Carlo analysis on the impact of this line-of-sight extrapolation noise on a greybody dust model consistent with Planck and Pan-STARRS observations, enabling us to quantify its effect. Using results from the Planck experiment, we find that this effect is small, more than an order of magnitude smaller than the current uncertainties. However, line-of-sight extrapolation noise may be a significant source of uncertainty in future low-noise primordial B-mode experiments. Scaling from Planck results, we find that accounting for this uncertainty becomes potentially important when experiments are sensitive to primordial B-mode signals with amplitude r≲0.0015 in the greybody dust models considered in this paper.
The standard cosmology is based on general relativity (GR) and includes dark matter and dark energy and predicts a fixed relationship between the gravitational potentials responsible for ...gravitational lensing and the matter overdensity. Alternative theories of gravity often make different predictions. We propose a set of measurements which can test this relationship, thereby distinguishing between dark energy or matter models and models in which gravity differs from GR. Planned surveys will be able to measure E(G), an observational quantity whose expectation value is equal to the ratio of the Laplacian of the Newtonian potentials to the peculiar velocity divergence, to percent accuracy. This will easily separate alternatives such as the cold dark matter model with a cosmological constant, Dvali-Gabadadze-Porrati, TeVeS, and f(R) gravity.
Systematic uncertainties that have been subdominant in past large-scale structure (LSS) surveys are likely to exceed statistical uncertainties of current and future LSS data sets, potentially ...limiting the extraction of cosmological information. Here we present a general framework (Principal Component Analysis – PCA – marginalization) to consistently incorporate systematic effects into a likelihood analysis. This technique naturally accounts for degeneracies between nuisance parameters and can substantially reduce the dimension of the parameter space that needs to be sampled. As a practical application, we apply PCA marginalization to account for baryonic physics as an uncertainty in cosmic shear tomography. Specifically, we use cosmolike to run simulated likelihood analyses on three independent sets of numerical simulations, each covering a wide range of baryonic scenarios differing in cooling, star formation, and feedback mechanisms. We simulate a Stage III (Dark Energy Survey) and Stage IV (Large Synoptic Survey Telescope/Euclid) survey and find a substantial bias in cosmological constraints if baryonic physics is not accounted for. We then show that PCA marginalization (employing at most three to four nuisance parameters) removes this bias. Our study demonstrates that it is possible to obtain robust, precise constraints on the dark energy equation of state even in the presence of large levels of systematic uncertainty in astrophysical processes. We conclude that the PCA marginalization technique is a powerful, general tool for addressing many of the challenges facing the precision cosmology programme.
One of the prime pieces of evidence for dark matter is the observation of large overdense regions in the Universe. To account for this observation, perturbations had to have grown since recombination ...by a factor greater than (1+z*) approximately 1180 where z* is the epoch of recombination. This enhanced growth does not happen in general relativity, and so dark matter is needed in the standard theory. We show here that enhanced growth can occur in alternatives to general relativity, in particular, in Bekenstein's relativistic version of modified Newtonian dynamics.
Cosmic microwave background (CMB) temperature anisotropies have and will
continue to revolutionize our understanding of cosmology. The recent discovery
of the previously predicted acoustic peaks in ...the power spectrum has
established a working cosmological model: a critical density universe
consisting of mainly dark matter and dark energy, which formed its structure
through gravitational instability from quantum fluctuations during an
inflationary epoch. Future observations should test this model and measure its
key cosmological parameters with unprecedented precision. The phenomenology and
cosmological implications of the acoustic peaks are developed in detail. Beyond
the peaks, the yet to be detected secondary anisotropies and polarization
present opportunities to study the physics of inflation and the dark energy.
The analysis techniques devised to extract cosmological information from
voluminous CMB data sets are outlined, given their increasing importance in
experimental cosmology as a whole.
A unified analysis of four cosmic shear surveys Chang, Chihway; Wang, Michael; Dodelson, Scott ...
Monthly Notices of the Royal Astronomical Society,
01/2019, Volume:
482, Issue:
3
Journal Article
The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the ...evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.
One way to explain the acceleration of the Universe is invoke dark energy parameterized by an equation of state w. Distance measurements provide one set of constraints on w, but dark energy also affects how rapidly structure grows; the greater the acceleration, the more suppressed the growth of structure. Upcoming surveys are therefore designed to probe w with direct observations of the distance scale and the growth of structure, each complementing the other on systematic errors and constraints on dark energy. A consistent set of results will greatly increase the reliability of the final answer.
Another possibility is that there is no dark energy, but that General Relativity does not describe the laws of physics accurately on large scales. While the properties of gravity have been measured with exquisite precision at stellar system scales and densities, within our solar system and by binary pulsar systems, its properties in different environments are poorly constrained. To fully understand if General Relativity is the complete theory of gravity we must test gravity across a spectrum of scales and densities. Rapid developments in gravitational wave astronomy and numerical relativity are directed at testing gravity in the high curvature, high density regime. Cosmological evolution provides a polar opposite test bed, probing how gravity behaves in the lowest curvature, low density environments.
There are a number of different implementations of astrophysically relevant modifications of gravity. Generically, the models are able to reproduce the distance measurements while at the same time altering the growth of structure. In particular, as detailed below, the Poisson equation relating over-densities to gravitational potentials is altered, and the potential that determines the geodesics of relativistic particles (such as photons) differs from the potential that determines the motion of non-relativistic particles. Upcoming surveys will exploit these differences to determine whether the acceleration of the Universe is due to dark energy or to modified gravity.
To realize this potential, both wide field imaging and spectroscopic redshift surveys play crucial roles. Projects including DES, eBOSS, DESI, PFS, LSST, Euclid, and WFIRST are in line to map more than a 1000cubic-billion-light-year volume of the Universe. These will map the cosmic structure growth rate to 1% in the redshift range 0<z<2, over the last 3/4 of the age of the Universe.
We demonstrate that the gravity wave background amplitude implies a robust upper bound on the wavelength-to-horizon ratio at the end of inflation: lambda/H(-1) less than or approximately equal e(60), ...as long as the cosmic energy density does not drop faster than radiation subsequent to inflation. This limit implies that N, the number of e-folds between horizon exit and the end of inflation for wave modes of interest, is less, similar 60 plus a model-dependent factor-for vast classes of slow-roll models, N less than or approximately equal 67. As an example, this bound solidifies the tension between observations of the cosmic microwave background anisotropies and chaotic inflation with a phi(4) potential by closing the escape hatch of large N (<62).
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