Materials of forums, conferences and seminars

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Browsing Materials of forums, conferences and seminars by Subject "dark energy"

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    Constraining Dark Energy Dynamics in Extended Parameter Space
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2017-04-03) Valentino, Eleonora Di; Melchiorri, Alessandro; Linder, Eric V.; Silk, Joseph
    Dynamical dark energy has been recently suggested as a promising and physical way to solve the 3 sigma tension on the value of the Hubble constant H0 between the direct measurement of Riess et al. (2016) (R16, hereafter) and the indirect constraint from Cosmic Microwave Anisotropies obtained by the Planck satellite under the assumption of a CDM model. In this paper, by parameterizing dark energy evolution using the w0-wa approach, and considering a 12 parameter extended scenario, we find that: a) the tension on the Hubble constant can indeed be solved with dynamical dark energy, b) a cosmological constant is ruled out at more than 95% c.l. by the Planck+R16 dataset, and c) all of the standard quintessence and half of the "downward going" dark energy model space (characterized by an equation of state that decreases with time) is also excluded at more than 95% c.l. These results are further confirmed when cosmic shear, CMB lensing, or SN Ia luminosity distance data are also included. However, tension remains with the BAO dataset. A cosmological constant and small portion of the freezing quintessence models are still in agreement with the Planck+R16+BAO dataset at between 68% and 95% c.l. Conversely, for Planck plus a phenomenological H0 prior, both thawing and freezing quintessence models prefer a Hubble constant of less than 70 km/s/Mpc. The general conclusions hold also when considering models with non-zero spatial curvature.
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    Cosmic Growth and Expansion Conjoined
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2016-10-17) Linder, Eric V.
    Cosmological measurements of both the expansion history and growth history have matured, and the two together provide an important test of general relativity. We consider their joint evolutionary track, showing that this has advantages in distinguishing cosmologies relative to considering them individually or at isolated redshifts. In particular, the joint comparison relaxes the shape degeneracy that makes f 8(z) curves difficult to separate from the overall growth amplitude. The conjoined method further helps visualization of which combinations of redshift ranges provide the clearest discrimination. We examine standard dark energy cosmologies, modified gravity, and “stuttering” growth, each showing distinct signatures.
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    The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: constraining modi ed gravity
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2016-12-02) Mueller, Eva-Maria; Percival, Will; Linder, Eric; Alam, Shadab; Zhao, Gong-Bo; Sanchez, Ariel G.; Beutler, Florian
    We use baryon acoustic oscillation and redshift space distortion from the completed Baryon Oscillation Spectroscopic Survey, corresponding to data release 12 of the Sloan Digital Sky Survey, combined sample analysis in combination with cosmic microwave background, supernova and redshift space distortion measurements from additional spectroscopic surveys to test deviations from general relativity. We present constraints on several phenomenological models of modi ed gravity: First, we parametrise the growth of structure using the growth index, nding = 0:566 0:058 (68% C.L.). Second, we modify the relation of the two Newtonian potentials by introducing two additional parameters, GM and GL. In this approach, GM refers to modi cations of the growth of structure whereas GL to modi cation of the lensing potential. We consider a power law to model the redshift dependency of GM and GL as well as binning in redshift space, introducing four additional degrees of freedom, GM(z < 0:5), GM(z > 0:5), GL(z < 0:5), GL(z > 0:5). At 68% C.L. we measure GM = 0:980 0:096 and GL = 1:082 0:060 for a linear model, GM = 1:01 0:36 and GL = 1:31 0:19 for a cubic model as well as GM(z < 0:5) = 1:26 0:32, GM(z > 0:5) = 0:986 0:022, GL(z < 0:5) = 1:067 0:058 and GL(z > 0:5) = 1:037 0:029. Thirdly, we investigate general scalar tensor theories of gravity, nding the model to be mostly unconstrained by current data. Assuming a one-parameter f(R) model we can constrain B0 < 7:7 10􀀀5 (95% C.L). For all models we considered we nd good agreement with general relativity.
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    Λ is Coming: Parametrizing Freezing Fields
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2017-03-21) Linder, Eric V.
    We explore freezing dark energy, where the evolution of the field approaches that of a cosmological constant at late times. We propose two general, two parameter forms to describe the class of freezing field models, in analogy to ones for thawing fields, here based on the physics of the flow parameter or the calibrated w–w′ phase space. Observables such as distances and Hubble parameters are fit to within 0.1%, and the dark energy equation of state generally to within better than 1%, of the exact numerical solutions.