Materials of forums, conferences and seminars

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Browsing Materials of forums, conferences and seminars by Subject "cosmology"

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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.