Topic
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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30 Jul 2009
TL;DR: In a series of five lectures as discussed by the authors, the authors reviewed inflationary cosmology and discussed the current observational evidence for inflation and opportunities for future tests of inflation are discussed, as well as the challenge of relating inflation to fundamental physics by giving an account of inflation in string theory.
Abstract: In a series of five lectures I review inflationary cosmology. I begin with a description of the initial conditions problems of the Friedmann-Robertson-Walker (FRW) cosmology and then explain how inflation, an early period of accelerated expansion, solves these problems. Next, I describe how inflation transforms microscopic quantum fluctuations into macroscopic seeds for cosmological structure formation. I present in full detail the famous calculation for the primordial spectra of scalar and tensor fluctuations. I then define the inverse problem of extracting information on the inflationary era from observations of cosmic microwave background fluctuations. The current observational evidence for inflation and opportunities for future tests of inflation are discussed. Finally, I review the challenge of relating inflation to fundamental physics by giving an account of inflation in string theory.
305 citations
TL;DR: In this article, the authors review cosmological aspects of brane world scenarios such as the Randall-Sundrum brane model and two-brane systems with a bulk scalar field.
Abstract: Recent developments in the physics of extra dimensions have opened up new avenues to test such theories. We review cosmological aspects of brane world scenarios such as the Randall–Sundrum brane model and two-brane systems with a bulk scalar field. We start with the simplest brane world scenario leading to a consistent cosmology: a brane embedded in an anti-de Sitter space–time. We generalize this setting to the case with a bulk scalar field and then to two-brane systems.We discuss different ways of obtaining a low-energy effective theory for two-brane systems, such as the moduli space approximation and the low-energy expansion. A comparison between the different methods is given. Cosmological perturbations are briefly discussed as well as early universe scenarios such as the cyclic model and the born-again brane world model. Finally we also present some physical consequences of brane world scenarios on the cosmic microwave background and the variation of constants.
305 citations
Ruhr University Bochum1, University of Edinburgh2, Swinburne University of Technology3, University College London4, Leiden University5, Max Planck Society6, Stanford University7, Polish Academy of Sciences8, Kapteyn Astronomical Institute9, Spanish National Research Council10, University of Bonn11, Astronomical Observatory of Capodimonte12, University of Oxford13, Princeton University14, Australian National University15, Chinese Academy of Sciences16, Korea Astronomy and Space Science Institute17, Shanghai Astronomical Observatory18
TL;DR: In this paper, a joint cosmological analysis of weak gravitational lensing observations from the Kilo-Degree Survey (KiDS-1000), with Baryon Oscillation Spectroscopic Survey (BOSS) and galaxy-galaxy lensing was presented.
Abstract: We present a joint cosmological analysis of weak gravitational lensing observations from the Kilo-Degree Survey (KiDS-1000), with
redshift-space galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey (BOSS) and galaxy-galaxy lensing
observations from the overlap between KiDS-1000, BOSS, and the spectroscopic 2-degree Field Lensing Survey (2dFLenS). This
combination of large-scale structure probes breaks the degeneracies between cosmological parameters for individual observables,
resulting in a constraint on the structure growth parameter S 8 = σ8
√
Ωm/0.3 = 0.766+0.020
−0.014, which has the same overall precision as
that reported by the full-sky cosmic microwave background observations from Planck. The recovered S 8 amplitude is low, however,
by 8.3 ± 2.6% relative to Planck. This result builds from a series of KiDS-1000 analyses where we validate our methodology with
variable depth mock galaxy surveys, our lensing calibration with image simulations and null-tests, and our optical-to-near-infrared
redshift calibration with multi-band mock catalogues and a spectroscopic-photometric clustering analysis. The systematic uncertainties identified by these analyses are folded through as nuisance parameters in our cosmological analysis. Inspecting the offset between
the marginalised posterior distributions, we find that the S 8-difference with Planck is driven by a tension in the matter fluctuation
amplitude parameter, σ8. We quantify the level of agreement between the cosmic microwave background and our large-scale structure
constraints using a series of different metrics, finding differences with a significance ranging between ∼ 3σ, when considering the
offset in S 8, and ∼2σ, when considering the full multi-dimensional parameter space.
305 citations
TL;DR: In this paper, the basic construction and cosmological implications of a power-counting renormalizable theory of gravitation, recently proposed by Hořava, are reviewed.
Abstract: Here we review the basic construction and cosmological implications of a power-counting renormalizable theory of gravitation, recently proposed by Hořava. We explain that (i) at low energy this theory does not exactly recover general relativity but instead mimics general relativity plus dark matter; (ii) higher spatial curvature terms allow bouncing and cyclic universes as regular solutions; (iii) the anisotropic scaling with the dynamical critical exponent z = 3 solves the horizon problem and leads to scale-invariant cosmological perturbations even without inflation. We also comment on issues related to an extra scalar degree of freedom called scalar graviton. In particular, for spherically-symmetric, static, vacuum configurations we prove non-perturbative continuity of the λ → 1 + 0 limit, where λ is a parameter in the kinetic action and general relativity has the value λ = 1. We also derive the condition under which linear instability of the scalar graviton does not show up.
304 citations
TL;DR: Spectroscopic observations of stars in the metal-poor globular cluster NGC 6397 reveal trends of atmospheric abundance with evolutionary stage for various elements that are reproduced by stellar-evolution models with diffusion and turbulent mixing and conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars.
Abstract: The measurement of the cosmic microwave background has strongly constrained the cosmological parameters of the Universe. When the measured density of baryons (ordinary matter) is combined with standard Big Bang nucleosynthesis calculations, the amounts of hydrogen, helium and lithium produced shortly after the Big Bang can be predicted with unprecedented precision. The predicted primordial lithium abundance is a factor of two to three higher than the value measured in the atmospheres of old stars. With estimated errors of 10 to 25%, this cosmological lithium discrepancy seriously challenges our understanding of stellar physics, Big Bang nucleosynthesis or both. Certain modifications to nucleosynthesis have been proposed, but found experimentally not to be viable. Diffusion theory, however, predicts atmospheric abundances of stars to vary with time, which offers a possible explanation of the discrepancy. Here we report spectroscopic observations of stars in the metal-poor globular cluster NGC6397 that reveal trends of atmospheric abundance with evolutionary stage for various elements. These element-specific trends are reproduced by stellar-evolution models with diffusion and turbulent mixing. We thus conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars by transporting the lithium deep into the star.
304 citations