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First map produced of universe 11 billion years ago

An international team of astronomers has produced the first map of the universe as it was 11 billion years ago, filling a gap between the Big Bang and the rapid expansion that followed. The study, published in the journal Astronomy & Astrophysics, shows the universe went through a phase roughly three billion years after the Big Bang when expansion actually started to slow, before the force of so-called 'dark energy' kicked in and sent galaxies accelerating away from each other.
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Quasars illustrate dark energy's roller coaster ride

Scientists have used a novel technique to probe the nature of dark energy some 10 billion years into the past.
They hope it will bring them closer to an explanation for the strange force that appears to be driving the Universe apart at an accelerating rate.

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Dark Energy Survey
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Synthetic universes: How simulations will help search for dark energy

The Dark Energy Survey is one of the most ambitious astrophysics experiments ever launched. For five years, a custom-designed camera mounted on a telescope in Chile will collect images of distant galaxies in the southern sky over an area of 5,000 square degrees, corresponding to roughly one-eighth of the visible universe.
That project will generate petabytes (thousands of terabytes) of data that must be painstakingly analysed by the collaboration of scientists from 27 institutions to find answers about the nature of dark energy, dark matter and the forces that shape the evolution of the universe.

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Title: Dark energy, matter creation and curvature
Authors: Victor H. Cardenas

The most studied way to explain the current accelerated expansion of the universe is to assume the existence of dark energy; a new component that fill the universe, does not clumps, currently dominates the evolution, and has a negative pressure. In this work I study an alternative model proposed by Lima et al. lima96, which does not need an exotic equation of state, but assumes instead the existence of gravitational particle creation. Because this model fits the supernova observations as well as the \Lambda CDM model, I perform in this work a thorough study of this model considering an explicit spatial curvature. I found that in this scenario we can alleviate the cosmic coincidence problem, basically showing that these two components, dark matter and dark energy, are of the same nature, but they act at different scales. I also shown the inadequacy of some particle creation models, and also I study a previously propose new model that overcome these difficulties.

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Title: Galaxy correlations and the BAO in a void universe: structure formation as a test of the Copernican Principle
Authors: Sean February, Chris Clarkson, Roy Maartens (Cape Town and Western Cape)

A suggested solution to the dark energy problem is the void model, where accelerated expansion is replaced by Hubble-scale inhomogeneity. In these models, density perturbations grow on a radially inhomogeneous background. This large scale inhomogeneity distorts the spherical Baryon Acoustic Oscillation feature into an ellipsoid which implies that the bump in the galaxy correlation function occurs at different scales in the radial and transverse correlation functions. We compute these for the first time, under the approximation that curvature gradients do not couple the scalar modes to vectors and tensors. The radial and transverse correlation functions are very different from those of the concordance model, even when the models have the same average BAO scale. This implies that if the models are fine-tuned to satisfy average BAO data, there is enough extra information in the correlation functions to distinguish a void model from LCDM. We expect these new features to remain when the full perturbation equations are solved, which means that the radial and transverse galaxy correlation functions can be used as a powerful test of the Copernican principle.

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Title: Dark energy from a renormalisation group flow
Authors: I. Mocioiu, R. Roiban

We present evidence that a special class of gravitationally-coupled hidden sectors, in which conformal invariance is dynamically broken in a controlled way, exhibit the properties of dark energy. Such quantum field theories may appear while embedding the Standard Model in a more fundamental high energy theory. At late times, an effective dark energy field behaves similarly to an exponentially small cosmological constant while at early times its energy density partly tracks that of matter.

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Title: Birth of Dark Energy by Quantum Metric Fluctuations in Imaginary Time
Authors: Leonid Marochnik

We show that in imaginary time quantum metric fluctuations of empty space form a self-consistent De Sitter gravitational instanton that can be thought of as describing the tunnelling from "nothing" into De Sitter space of real time (no cosmological constant or scalar fields are needed). The first time, this mechanism is activated to give birth to a flat inflationary Universe. The second time, it is turned on to complete cosmological evolution of the Universe after energy density of matter drops below the threshold (energy density of instantons). An accelerated expansion takes over after the scale factor exceeds this threshold, which marks the birth of dark energy at the redshift 1+z=1.44 and provides a possible solution to the "coincidence problem". The number of gravitons which tunnelled into the Universe must be of the order of 10^122 to create the observational value of the Hubble constant. This number has nothing to do with vacuum energy, which is a possible solution to the "old cosmological constant problem". The emptying Universe should possibly complete its evolution by tunnelling back to "nothing". After that, the entire scenario is repeated, and it can happen endlessly.

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 New Cosmological Insights from the South Pole Telescope

Analysis of data from the 10-meter South Pole Telescope (SPT) is providing new support for the most widely accepted explanation of dark energy - the mysterious force that is responsible for the accelerating expansion of the universe. The data strongly support Einstein's cosmological constant, even though the analysis was based on only a fraction of the SPT data collected and only 100 of the over 500 galaxy clusters detected so far.
The results also are beginning to home in on the masses of neutrinos, the most abundant particles in the universe.

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Title: Natural Quintessence in String Theory
Authors: Michele Cicoli, Francisco G. Pedro, Gianmassimo Tasinato

We introduce a natural model of quintessence in string theory where the light rolling scalar is radiatively stable and couples to Standard Model matter with weaker-than- Planckian strength. The model is embedded in an anisotropic type IIB compactification with two exponentially large extra dimensions and TeV-scale gravity. The bulk turns out to be nearly supersymmetric since the scale of the gravitino mass is of the order of the observed value of the cosmological constant. The quintessence field is a modulus parameterising the size of an internal four-cycle which naturally develops a potential of the order (gravitino mass)^4, leading to a small dark energy scale without tunings. The mass of the quintessence field is also radiatively stable since it is protected by supersymmetry in the bulk. Moreover, this light scalar couples to ordinary matter via its mixing with the volume mode. Due to the fact that the quintessence field is a flat direction at leading order, this mixing is very small, resulting in a suppressed coupling to Standard Model particles which avoids stringent fifth-force constraints. On the other hand, if dark matter is realised in terms of Kaluza-Klein states, unsuppressed couplings between dark energy and dark matter can emerge, leading to a scenario of coupled quintessence within string theory. We study the dynamics of quintessence in our set-up, showing that its main features make it compatible with observations.

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Clocking an Accelerating Universe: First Results from BOSS

Berkeley Lab scientists are the leaders of BOSS, the Baryon Oscillation Spectroscopic Survey. They and their colleagues in the third Sloan Digital Sky Survey have announced the most precise measurements ever made of the era when dark energy turned on.
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