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Item Open Access A Personal View on a Zero Carbon Future(International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017, 2017-07-12) Winter, AxelShow more Item Open Access Accelerated Parameter Estimation with DALE X(NURIS; Energetic Cosmos Laboratory, 2017-05-08) Daniel, Scott F.; Linder, Eric V.Show more 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 con-tours for accurate error estimation. We employ DALEχ(Direct Analysis of Limits via the Exterior ofχ2) 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 DALEχfinds the same confidence limit as Multi-Nest using roughly an order of magnitude fewer evaluations of the likelihood function.DALE χ is open-source and available athttps://github.com/danielsf/Dalex.git.Show more Item Open Access 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.Show more 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 .Show more Item Open Access ALIGNING CLIMATE CHANGE ACTION AND SUSTAINABLE DEVELOPMENT GOALS(International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017, 2017) Sokona, YoubaShow more Item Open Access Association of renewable energy of Kazakhstan(International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017, 2017-07-12) Kashkinbekov, ArmanShow more Item Open Access ASTANA SOLAR LLP. Manufacture of photovoltaic panels in the Republic of Kazakhstan(International Scientific and University Conference. "Climate Change and CO2 Emission Reduction", 2017-07) Kikbayev, AlexanderShow more Item Open Access The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Constraining modified gravity(American Physical Society, 2016-12-02) Mueller, Eva-Maria; Percival, Will; Linder, Eric; Alam, Shadab; Zhao, Gong-Bo; Sanchez, Ariel G.; Beutler, FlorianShow more 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 the 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 modified gravity.Show more Item Open Access Constraining dark energy dynamics in extended parameter space(American Physical Society, 2017-07-19) Di Valentino, Eleonora; Melchiorri, Alessandro; Linder, Eric V.; Silk, JosephShow more 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 ΛCDM model. In this paper, by parametrizing 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. The best fit value of the χ2 for the Planck+R16 data set improves by Δχ2=−12.9 when moving to 12 parameters respect to standard ΛCDM. 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 data set 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 nonzero spatial curvature.Show more Item Open Access 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, JosephShow more 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.Show more Item Open Access Cosmic Curvature Tested Directly from Observations(NURIS; Energetic Cosmos Laboratory, 2018-02-13) Denissenya, Mikhail; Linder, Eric V.; Shafieloo, ArmanShow more Cosmic spatial curvature is a fundamental geometric quantity of the Universe. We investigate a model independent, geometric approach to measure spatial curvature directly from observations,without any derivatives of data. This employs strong lensing time delays and supernova distance measurements to measure the curvature itself, rather than just testing consistency with flatness.We define two curvature estimators, with differing error propagation characteristics, that can cross-check each other, and also show how they can be used to map the curvature in redshift slices, totest constancy of curvature as required by the Robertson-Walker metric. Simulating realizations ofredshift distributions and distance measurements of lenses and sources, we estimate uncertainties onthe curvature enabled by next generation measurements. Theresults indicate that the model independent methods, using only geometry without assuming forms for the energy density constituents,can determine the curvature at the∼6×10^−3 level.Show more Item Open Access Cosmic Growth and Expansion Conjoined(International conference "ECL17: Exploring the Energetic Universe 2017", Nazarbayev University Energetic Cosmic Laboratory, 2016-10-17) Linder, Eric V.Show more 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.Show more Item Open Access Cosmic growth and expansion conjoined(2017-01-31) Linder, Eric V.; Linder, Eric V.Show more 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.Show more Item Open Access 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.Show more 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.Show more Item Open Access Cosmic Growth Signatures of Modified Gravitational Strength(NURIS; Energetic Cosmos Laboratory, 2018-09-05) Denissenya, Mikhail; Linder, Eric V.Show more 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 ina 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% uncertaintyShow more Item Open Access Dark Energy from α-attractors: Phenomenology and Observational Constraints(NURIS; Energetic Cosmos Laboratory, 2018-03-01) Garcia-Garcia, Carlos; Linder, Eric V.; Ruiz-Lapuente, Pilar; Zumalacaregui, MiguelShow more The possibility of linking inflation and late cosmic accelerated expansion using the α-attractor models has received increasing attention due to their physical motivation. In the early universe, α-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally α-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this paper we study a generalized dark energy α-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that 1+w∼1/α (while the gravitational wave power r∼α) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 compressed likelihood), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions.Show more Item Open Access Debiasing Cosmic Gravitational Wave Sirens [Article](NURIS; Energetic Cosmos Laboratory, 2019-05-27) Keeley, Ryan E.; Shafieloo, Arman; L'Huillier, Benjamin; Linder, Eric V.Show more Accurate estimation of the Hubble constant, and other cosmological parameters, from distances measured by cosmic gravitational wave sirens requires sufficient allowance for the dark energy evolution. We demonstrate how model independent statistical methods, specifically Gaussian process regression, can remove bias in the reconstruction of H(z), and can be combined model independently with supernova distances.Show more Item Open Access Deep decarbonisation and growth: challenges and prospects(National Research University “Higher School of Economics” Moscow, Russia. International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017, 2017-07-12) Safonov, GeorgyShow more Item Open Access Developments in Cosmic Growth and Gravitation [Article](NURIS; Energetic Cosmos Laboratory, 2019-04-23) Linder, Eric V.Show more Cosmic surveys of large scale structure have imaged hundreds of millions of galaxies and mapped the 3D positions of over a million. Surveys starting over the next few years will increase these numbers more than tenfold. Simultaneously, developments in extracting information on dark energy, dark matter, neutrinos, and gravity on cosmic scales have advanced greatly, with many important works from Asian institutions.Show more Item Open Access EDUCATION FOR SUSTAINABLE DEVELOPMENT(UNIVERSITY OF DONJA GORICA, MONTENEGRO. International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017. Astana. Kazakhstan., 2017-07) Vukotic, VeselinShow more Item Open Access ELECTRIFYING AFRICA(International Scientific and University Conference. "Climate Change and CO2 Emission Reduction" 12-13 July, 2017, 2017-07) Andrieu, PriscilliaShow more