Browsing by Author "Linder, Eric V."

Now showing 1 - 7 of 7
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    Accelerated Parameter Estimation with DALEX
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2017-05-02) Daniel, Scott F.; Linder, Eric V.
    We consider methods for improving the estimation of constraints on a high-dimensional parameter space with a computationally expensive likelihood function. In such cases, Markov chain Monte Carlo (MCMC) can take a long time to converge and concentrates on finding the maxima rather than the often-desired confidence contours for accurate error estimation. We employ DALEχ (Direct Analysis of Limits via the Exterior of χ2) for determining confidence contours by minimizing a cost function parametrized to incentivize points in parameter space which are both on the confidence limit and far from previously sampled points. We compare DALEχ to the nested sampling algorithm implemented in MultiNest on a toy likelihood function that is highly non-Gaussian and non-linear in the mapping between parameter values and χ2. We find that in high-dimensional cases DALEχ finds the same confidence limit as Multi-Nest using roughly an order of magnitude fewer evaluations of the likelihood function. DALEχ is open-source and available at https://github.com/danielsf/Dalex.git .
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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
    (2017-01-31) Linder, Eric V.; Linder, Eric V.
    Abstract 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 fσ8(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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    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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    Cosmic Growth Signatures of Modified Gravitational Strength
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2017-03-02) Denissenya, Mikhail; Linder, Eric V.
    Cosmic growth of large scale structure probes the entire history of cosmic expansion and gravitational coupling. To get a clear picture of the effects of modification of gravity we consider a deviation in the coupling strength (effective Newton’s constant) at different redshifts, with different durations and amplitudes. We derive, analytically and numerically, the impact on the growth rate and growth amplitude. Galaxy redshift surveys can measure a product of these through redshift space distortions and we connect the modified gravity to the observable in a way that may provide a useful parametrization of the ability of future surveys to test gravity. In particular, modifications during the matter dominated era can be treated by a single parameter, the “area” of the modification, to an accuracy of 0.3% in the observables. We project constraints on both early and late time gravity for the Dark Energy Spectroscopic Instrument and discuss what is needed for tightening tests of gravity to better than 5% uncertainty.
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    Slicing the Vacuum: New Accelerating Mirror Solutions of the Dynamical Casimir Effect
    (International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2017-07-17) Good, Michael R.R.; Linder, Eric V.
    Radiation from accelerating mirrors in a Minkowski spacetime provides insights into the nature of horizons, black holes, and entanglement entropy. We introduce new, simple, symmetric and analytic moving mirror solutions and study their particle, energy, and entropy production. This includes an asymptotically static case with nite emission that is the black hole analog of complete evaporation. The total energy, total entropy, total particles, and spectrum are the same on both sides of the mirror. We also study its asymptotically inertial, drifting analog (which gives a black hole remnant) to explore di erences in nite and in nite production.
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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.