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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TL;DR: In this paper, the cosmology of the general f(T) gravity theory was studied, and the modified Einstein equations were expressed using covariant quantities, and derived the gauge-invariant perturbation equations in covariant form.
Abstract: In this work we study the cosmology of the general f(T) gravity theory. We express the modified Einstein equations using covariant quantities, and derive the gauge-invariant perturbation equations in covariant form. We consider a specific choice of f(T), designed to explain the observed late-time accelerating cosmic expansion without including an exotic dark energy component. Our numerical solution shows that the extra degree of freedom of such f(T) gravity models generally decays as one goes to smaller scales, and consequently its effects on scales such as galaxies and galaxies clusters are small. But on large scales, this degree of freedom can produce large deviations from the standard �CDM scenario, leading to severe constraints on the f(T) gravity models as an explanation to the cosmic acceleration.
299 citations
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Princeton University1, Cardiff University2, Pontifical Catholic University of Chile3, Université Paris-Saclay4, University of Pennsylvania5, University of Oxford6, Johns Hopkins University7, University of British Columbia8, Cornell University9, National Institute of Standards and Technology10, University of Michigan11, University of Toronto12, University of Chile13, University of Chicago14, Stanford University15, University of KwaZulu-Natal16, University of California, Berkeley17, University of Cambridge18, Goddard Space Flight Center19, Lawrence Berkeley National Laboratory20, Florida State University21, University of Southern California22, University of Arizona23, University of Pittsburgh24, Stony Brook University25, Pennsylvania State University26, Columbia University27, Rutgers University28, Yale University29, Perimeter Institute for Theoretical Physics30, University of Illinois at Urbana–Champaign31, University of Milan32, Haverford College33, California Institute of Technology34, McGill University35, Pontifical Catholic University of Valparaíso36, West Chester University of Pennsylvania37, Carnegie Mellon University38, Arizona State University39
TL;DR: In this article, the Atacama Cosmology Telescope (ACT) data were used to estimate the temperature and polarization anisotropy from the cosmic microwave background (CMB) at 98 and 150 GHz.
Abstract: We present new arcminute-resolution maps of the Cosmic Microwave Background temperature and polarization anisotropy from the Atacama Cosmology Telescope, using data taken from 2013–2016 at 98 and 150 GHz. The maps cover more than 17,000 deg2, the deepest 600 deg2 with noise levels below 10μK-arcmin. We use the power spectrum derived from almost 6,000 deg2 of these maps to constrain cosmology. The ACT data enable a measurement of the angular scale of features in both the divergence-like polarization and the temperature anisotropy, tracing both the velocity and density at last-scattering. From these one can derive the distance to the last-scattering surface and thus infer the local expansion rate, H0. By combining ACT data with large-scale information from WMAP we measure H0=67.6± 1.1 km/s/Mpc, at 68% confidence, in excellent agreement with the independently-measured Planck satellite estimate (from ACT alone we find H0=67.9± 1.5 km/s/Mpc). The ΛCDM model provides a good fit to the ACT data, and we find no evidence for deviations: both the spatial curvature, and the departure from the standard lensing signal in the spectrum, are zero to within 1σ; the number of relativistic species, the primordial Helium fraction, and the running of the spectral index are consistent with ΛCDM predictions to within 1.5–2.2σ. We compare ACT, WMAP, and Planck at the parameter level and find good consistency; we investigate how the constraints on the correlated spectral index and baryon density parameters readjust when adding CMB large-scale information that ACT does not measure. The DR4 products presented here will be publicly released on the NASA Legacy Archive for Microwave Background Data Analysis.
298 citations
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TL;DR: In this article, the authors extended the general relativistic description of galaxy clustering developed in Yoo, Fitzpatrick, and Zaldarriaga (2009) to the case of galaxy power spectrum.
Abstract: We extend the general relativistic description of galaxy clustering developed in Yoo, Fitzpatrick, and Zaldarriaga (2009). For the first time we provide a fully general relativistic description of the observed matter power spectrum and the observed galaxy power spectrum with the linear bias ansatz. It is significantly different from the standard Newtonian description on large scales and especially its measurements on large scales can be misinterpreted as the detection of the primordial non-Gaussianity even in the absence thereof. The key difference in the observed galaxy power spectrum arises from the real-space matter fluctuation defined as the matter fluctuation at the hypersurface of the observed redshift. As opposed to the standard description, the shape of the observed galaxy power spectrum evolves in redshift, providing additional cosmological information. While the systematic errors in the standard Newtonian description are negligible in the current galaxy surveys at low redshift, correct general relativistic description is essential for understanding the galaxy power spectrum measurements on large scales in future surveys with redshift depth z ≥ 3. We discuss ways to improve the detection significance in the current galaxy surveys and comment on applications of our general relativistic formalism in future surveys.
298 citations
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TL;DR: In this paper, a new class of gravity theories is proposed in which they add a new degree of freedom, the Aether, in the form of a vector field that is coupled covariantly, but non-minimally, with the space-time metric.
Abstract: There is evidence that Newton and Einstein's theories of gravity cannot explain the dynamics of a universe made up solely of baryons and radiation. To be able to understand the properties of galaxies, clusters of galaxies and the universe on the whole it has become commonplace to invoke the presence of dark matter. An alternative approach is to modify the gravitational field equations to accommodate observations. We propose a new class of gravitational theories in which we add a new degree of freedom, the Aether, in the form of a vector field that is coupled covariantly, but nonminimally, with the space-time metric. We explore the Newtonian and non-Newtonian limits, discuss the conditions for these theories to be consistent and explore their effect on cosmology.
298 citations
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01 Jan 2011
TL;DR: The Cycle of Time as mentioned in this paper provides a new perspective on cosmology, providing a quite unexpected answer to the often-asked question "what came before the Big Bang?" The two key ideas underlying this novel proposal are a penetrating analysis the Second Law of thermodynamics - according to which the randomness of our world is continually increasing - and a thorough examination of the light-cone geometry of space-time.
Abstract: Roger Penrose's groundbreaking and bestselling "The Road to Reality" provided a comprehensive yet readable guide to our present understanding of the laws that are currently believed to govern our universe. In "Cycles of Time", he moves far beyond this to develop a completely new perspective on cosmology, providing a quite unexpected answer to the often-asked question, 'what came before the Big Bang'? The two key ideas underlying this novel proposal are a penetrating analysis the Second Law of thermodynamics - according to which the 'randomness' of our world is continually increasing - and a thorough examination of the light-cone geometry of space-time. Penrose is able to combine these two central themes to show how the expected ultimate fate of our accelerating, expanding universe can actually be reinterpreted as the 'Big Bang' of a new one. On the way, many other basic ingredients are presented, and their roles discussed in detail, though without any complex mathematical formulae (these all being banished to the appendices). Various standard and non-standard cosmological models are presented, as is the fundamental and ubiquitous role of the cosmic microwave background. Also crucial to the discussion are the huge black holes lying in galactic centres, and their eventual disappearance via the mysterious process of Hawking evaporation.
296 citations