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TOPIC: Dark Energy


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RE: Dark Energy
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Dark energy the mysterious entity that is speeding up the expansion of the universe has been present for at least 9 billion years, suggests a study of the most distant supernova explosions ever recorded. It appears to have been a repulsive force even in these early times, casting doubt on models that suggest it was once attractive.
Astronomers measure cosmic distances with type Ia supernovae, which all explode with about the same brightness. Because light travels at a finite speed, more distant supernovae are also further back in time.
In the 1990s, studies of these supernovae revealed they were dimmer than expected in the past, revealing the universe is expanding faster and faster.

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Got Questions About Dark Energy?

What is dark energy? Good question. Nobody quite knows what causes the expansion of the universe to accelerate or makes up the observed deficit in the cosmic inventory of matter, but at least they've roped off this area of ignorance and given it a spiffy name. I'm not being entirely facetious: the first task of science is to identify and classify unknown phenomena. Only then does explanation become possible. The nature of dark energy is probably the single biggest question in physics and astronomy today (which is saying a lot).

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NASA Schedules Dark Energy Discovery Media Teleconference

NASA will host a media teleconference with Hubble Space Telescope astronomers at 1 p.m. EST Thursday, Nov. 16, to announce the discovery that dark energy has been an ever-present constituent of space for most of the universe's history.

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Title: Cosmic microwave background and large-scale structure constraints on a simple quintessential inflation model
Authors: Rogerio Rosenfeld, Joshua A. Frieman

We derive constraints on a simple quintessential inflation model, based on a spontaneously broken Phi^4 theory, imposed by the Wilkinson Microwave Anisotropy Probe three-year data (WMAP3) and by galaxy clustering results from the Sloan Digital Sky Survey(SDSS). We find that the scale of symmetry breaking must be larger than about 3 Planck masses in order for inflation to generate acceptable values of the scalar spectral index and of the tensor-to-scalar ratio. We also show that the resulting quintessence equation-of-state can evolve rapidly at recent times and hence can potentially be distinguished from a simple cosmological constant in this parameter regime.

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Neutrino mixing
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Title: Neutrino mixing as a source of dark energy
Authors: A.Capolupo, S.Capozziello, G.Vitiello
Version 3

We show that the vacuum condensate due to neutrino mixing in quantum field theory (QFT) contributes to the dark energy budget of the universe which gives rise to the accelerated behaviour of cosmic flow. The mechanism of neutrino mixing is therefore a possible candidate to contribute to the cosmological dark energy.

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Title: Dark Energy and Some Alternatives: a Brief Overview
Authors: J.S. Alcaniz (observatorio Nacional)

The high-quality cosmological data, which became available in the last decade, have thrusted upon us a rather preposterous composition for the universe which poses one of the greatest challenges theoretical physics has ever faced: the so-called dark energy. By focusing our attention on specific examples of dark energy scenarios, we discuss three different candidates for this dark component, namely, a decaying vacuum energy or time-varying cosmological constant (Λ (t)), a rolling homogeneous quintessence field (Φ), and modifications in gravity due to extra spatial dimensions. As discussed, all these candidates (along with the vacuum energy or cosmological constant (Λ)) seem somewhat to be able to explain the current observational results, which hampers any definitive conclusion on the actual nature of the dark energy.

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Title: The impact of neutrino masses on the determination of dark energy properties
Authors: Axel De La Macorra, Alessandro Melchiorri, Paolo Serra, Rachel Bean

Recently, the Heidelberg-Moscow double beta decay experiment has claimed a detection for a neutrino mass with high significance. Here we consider the impact of this measurement on the determination of the dark energy equation of state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and other cosmological datasets we constrain the equation of state to -1.67< w <-1.05 at 95% c.l., ruling out a cosmological constant at more than 95% c.l.. Interestingly enough, coupled neutrino-dark energy models may be consistent with such equation of state. While future data are certainly needed for a confirmation of the controversial Heildelberg-Moscow claim, our result shows that future laboratory searches for neutrino masses may play a crucial role in the determination of the dark energy properties.

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Title: Critical point corresponding to Big Rip in SO(1,1) dark energy model
Authors: Yi-Huan Wei

In the hessence dark energy model, the critical point of the autonomous system with the field Φ=0 for the inverse power law potential corresponds to the future Big Rip of phantom universe. The existence of the interaction term C doesn't change the critical point if it behaves as C~τ^ p with p>(2/n)-2-(γm/2) at late times. The result of linear perturbation analysis shows that the critical point is unstable.

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Title: Dark Energy Constraints from Gemini Deep Deep Survey
Authors: M.A. Dantas (ON), J.S. Alcaniz (ON), D. Jain (Univ. of Delhi), A. Dev (Univ. of Delhi)

Dark energy is the invisible fuel that seems to drive the current acceleration of the Universe. Its presence, which is inferred from an impressive convergence of high-quality observational results along with some successful theoretical predictions, is also supported by the current estimates of the age of the Universe from dating of local and high-z objects. In this work researchers study observational constraints on the dark energy equation of state (w) from lookback time measurements of high-z galaxies, as recently published by the Gemini Deep Deep Survey (GDDS).
In order to build up their lookback time sample from these observations they use 8 high-z galaxies in the redshift interval 1.3 ≤ z ≤ 2.2 and assume the total expanding age of the Universe to be t_0^obs = 13.6 0.2 billion years, as obtained from current large scale structure and cosmic microwave background data. They show that these age measurements are compatible with values of w close to -1, although there is still space for quintessence (w > -1) and phantom (w < -1) behaviours. In order to break possible degeneracies in the Omega_m - w plane, they also discuss the bounds on this parametric space when GDDS lookback time measurements are combined with the most recent SNe Ia, CMB and LSS data.

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New Universal Constant
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Title: A New Universal Constant Determining Expansion of the Universe
Authors: Charles B. Leffert

A new universal constant of expansion has been discovered with amazing predictive power once its density-time relations have been deciphered. The new constant is kappa, the product of the gravitational constant, and the average total mass-energy density of our universe and the square of the cosmic time. With the ten parameters known, this relation promises to account for the expansion of our universe from its beginning into the far future. The most important and most difficult item is cosmic time and its scaling relation with the densities.
The new cosmological theory will be presented in this paper to show good predictions of the cosmological parameters. The theory will be used in a second paper to show that acceleration of the expansion rate is not needed to account globally for the exploding-star supernova Ia radiation that has travelled such great distances in our expanding universe.

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