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Cosmology

About: Cosmology is a research topic. Over the lifetime, 18004 publications have been published within this topic receiving 631028 citations. The topic is also known as: physical cosmology & cosmologies.


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Journal ArticleDOI
TL;DR: In this article, BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves.
Abstract: BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyze the BICEP2 results and show that the 100x150 GHz and 150x150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarization signal. We give independent estimates of the dust polarization signal in the BICEP2 region using four different approaches. While these approaches are consistent with each other, the expected amplitude of the dust polarization power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarization angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin. (abridged)

214 citations

Journal ArticleDOI
TL;DR: A review of large-scale motions in the universe can be found in this article, with emphasis on the theoretical implications of the proposed motion models and their application in the field of cosmology.
Abstract: The editors suggested a review entitled "Are There Large-Scale Motions in the Universe?". The answer is "yes," in the sense that the interpretation of the data as motions is the simplest model, so far consistent with all other available data under the current "standard model" of physical cosmology. I review tests that could have ended up falsifying this model and failed, but the scope of this review is much extended as the field has developed far beyond the question of existence of motions. With the motions being accepted as a working hypothesis, the study of large-scale dynamics is becoming a mature scientific field where observation and theory are confronted in a quantitative way. It is this area of major activity in cosmology that is addressed here. I make no attempt to provide a complete reference list, nor do I try to achieve a balanced discussion of all the issues of relevance and authors involved. My goal is to provide a critical account of some of the issues in this field that I find important, with emphasis on theoretical implications. In many cases I quote only a recent paper automatically implying "and references therein." The reader is referred to a comprehensive, observation-oriented review of large­ scale motions in historical perspective by Burstein ( 1990b), a detailed review of distance indicators in a collection of essays by Jacoby et al ( 1992), and to Principles of Physical Cosmology by Peebles ( 1993). The current phase of the field was seeded by two major developments. One was the confirmation of the dipole moment in the Cosmic Microwave Back­ ground (CMB) (Corey & Wilkinson 1976, Smoot et al 1977), indicating via Doppler shift that the Local Group of galaxies (LG) is moving at rv600 Ian S-1 relative to the cosmological frame defined by the CMB. The other was the in­ vention of methods for inferring distances independent of redshifts based on intrinsic relations between galaxy quantities (Section 3; Tully & Fisher 1977,

214 citations

Posted Content
TL;DR: Non-Gaussianity, i.e., the study of nonGaussian contributions to the correlations of cosmological fluctuations, will become an important probe of both the early and the late Universe as discussed by the authors.
Abstract: A new and powerful probe of the origin and evolution of structures in the Universe has emerged and been actively developed over the last decade. In the coming decade, non-Gaussianity, i.e., the study of non-Gaussian contributions to the correlations of cosmological fluctuations, will become an important probe of both the early and the late Universe. Specifically, it will play a leading role in furthering our understanding of two fundamental aspects of cosmology and astrophysics: (i) the physics of the very early universe that created the primordial seeds for large-scale structures, and (ii) the subsequent growth of structures via gravitational instability and gas physics at later times. To date, observations of fluctuations in the Cosmic Microwave Background (CMB) and the Large-Scale Structure of the Universe (LSS) have focused largely on the Gaussian contribution as measured by the two-point correlations (or the power spectrum) of density fluctuations. However, an even greater amount of information is contained in non-Gaussianity and a large discovery space therefore still remains to be explored. Many observational probes can be used to measure non-Gaussianity, including CMB, LSS, gravitational lensing, Lyman-alpha forest, 21-cm fluctuations, and the abundance of rare objects such as clusters of galaxies and high-redshift galaxies. Not only does the study of non-Gaussianity maximize the science return from a plethora of present and future cosmological experiments and observations, but it also carries great potential for important discoveries in the coming decade.

214 citations

Journal ArticleDOI
Lee Smolin1
TL;DR: In this article, a new type of explanatory mechanism is proposed to account for the fact that many of the dimensionless numbers which characterize particle physics and cosmology take unnatural values, and three possible examples of this mechanism are described.
Abstract: A new type of explanatory mechanism is proposed to account for the fact that many of the dimensionless numbers which characterize particle physics and cosmology take unnatural values. It is proposed that all final singularities 'bounce' or tunnel to initial singularities of new universes at which point the dimensionless parameters of the standard models of particle physics and cosmology undergo small random changes. This speculative hypothesis, plus the conventional physics of gravitational collapse, together comprise a mechanism for natural selection, in which those choices of parameters that lead to universes that produce the most black holes during their lifetime are selected for. If our Universe is a typical member of the ensemble that results from many generations of such reproducing universes then it follows that the parameters of our present Universe are near a local maximum of the number of black holes produced per universe. Thus, modifications of the parameters of particle physics and cosmology from their present values should tend to decrease the number of black holes in the universe. Three possible examples of this mechanism are described.

214 citations

Book
27 Apr 2015
TL;DR: In this paper, the authors present the foundations of effective field theory, string theory, and string compactifications, setting the stage for a detailed examination of models of inflation in string theory.
Abstract: The past two decades have seen transformative advances in cosmology and string theory. Observations of the cosmic microwave background have revealed strong evidence for inflationary expansion in the very early universe, while new insights about compactifications of string theory have led to a deeper understanding of inflation in a framework that unifies quantum mechanics and general relativity. Written by two of the leading researchers in the field, this complete and accessible volume provides a modern treatment of inflationary cosmology and its connections to string theory and elementary particle theory. After an up-to-date experimental summary, the authors present the foundations of effective field theory, string theory, and string compactifications, setting the stage for a detailed examination of models of inflation in string theory. Three appendices contain background material in geometry and cosmological perturbation theory, making this a self-contained resource for graduate students and researchers in string theory, cosmology, and related fields.

213 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
2023768
20221,518
2021737
2020784
2019782