We present the most general parametrization of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. We follow and extend the parametrized post-Friedmannian ...approach, previously applied to modified gravity theories, in order to include interacting dark energy. We demonstrate its use through a number of worked examples and show how the initially large parameter space of free functions can be significantly reduced and constrained to include only a few nonzero coefficients. This paves the way for a model-independent approach to classify and test interacting dark energy theories.
Models of dark matter coupled to dark energy Pourtsidou, A.; Skordis, C.; Copeland, E. J.
Physical review. D, Particles, fields, gravitation, and cosmology,
10/2013, Letnik:
88, Številka:
8
Journal Article
Recenzirano
Odprti dostop
We present three distinct types of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. Our construction draws from the pull-back formalism for fluids and ...generalizes the fluid action to involve couplings to the scalar field. We investigate the cosmology of each class of model both at the background and linearly perturbed level. We choose a potential for the scalar field and a specific coupling function for each class of models and we compute the cosmic microwave background and matter power spectra.
ABSTRACT
We derive constraints on a coupled quintessence model with pure momentum exchange from the public ∼1000 deg2 cosmic shear measurements from the Kilo-Degree Survey and the Planck 2018 cosmic ...microwave background data. We compare this model with Lambda cold dark matter and find similar χ2 and log-evidence values. We accelerate parameter estimation by sourcing cosmological power spectra from the neural network emulator CosmoPower. We highlight the necessity of such emulator-based approaches to reduce the computational runtime of future similar analyses, particularly from Stage IV surveys. As an example, we present Markov Chain Monte Carlo forecasts on the same coupled quintessence model for a Euclid-like survey, revealing degeneracies between the coupled quintessence parameters and the baryonic feedback and intrinsic alignment parameters, but also highlighting the large increase in constraining power Stage IV surveys will achieve. The contours are obtained in a few hours with CosmoPower, as opposed to the few months required with a Boltzmann code.
We explore the potential of using intensity mapping surveys (MeerKAT, SKA) and optical galaxy surveys (DES, LSST) to detect H i clustering and weak gravitational lensing of 21 cm emission in auto- ...and cross-correlation. Our forecasts show that high-precision measurements of the clustering and lensing signals can be made in the near future using the intensity mapping technique. Such studies can be used to test the intensity mapping method, and constrain parameters such as the H i density
$\Omega _{\rm H\,\small {I}}$
, the H i bias
$b_{\rm H\,\small {I}}$
and the galaxy-H i correlation coefficient
$r_{\rm H\,\small {I}-g}$
.
ABSTRACT
We embed linear and non-linear parametrizations of beyond standard cosmological physics in the halo model reaction framework, providing a model-independent prescription for the non-linear ...matter power spectrum. As an application, we focus on Horndeski theories, using the Effective Field Theory of Dark Energy (EFTofDE) to parametrize linear and quasi-non-linear perturbations. In the non-linear regime, we investigate both a non-linear parametrized post-Friedmann (nPPF) approach as well as a physically motivated and approximate phenomenological model based on the error function (Erf). We compare the parametrized approaches’ predictions of the non-linear matter power spectrum to the exact solutions, as well as state-of-the-art emulators, in an evolving dark energy scenario and two well-studied modified gravity models, finding sub-per cent agreement in the reaction using the Erf model at z ≤ 1 and k ≤ 5 h Mpc−1. This suggests only an additional three free constants, above the background and linear theory parameters, are sufficient to model non-linear, non-standard cosmology in the matter power spectrum at scales down to k ≤ 3h Mpc−1 within $2{{\ \rm per\ cent}}$ accuracy. We implement the parametrizations into ver.2.0 of the ReACT code: ACTio et ReACTio.
H i intensity mapping: a single dish approach Battye, R. A.; Browne, I. W. A.; Dickinson, C. ...
Monthly Notices of the Royal Astronomical Society,
09/2013, Letnik:
434, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We discuss the detection of large-scale H i intensity fluctuations using a single dish approach with the ultimate objective of measuring the baryonic acoustic oscillations (BAO) and constraining the ...properties of dark energy. To characterize the signal we present 3D power spectra, 2D angular power spectra for individual redshift slices and also individual line-of-sight spectra computed using the S3 simulated H i catalogue which is based on the Millennium Simulation. We consider optimal instrument design and survey strategies for a single dish observation at low and high redshift for a fixed sensitivity. For a survey corresponding to an instrument with T
sys = 50 K, 50 feedhorns and 1 year of observations, we find that at low redshift (z 0.3), a resolution of ∼40 arcmin and a survey of ∼5000 deg2 is close to optimal, whereas at higher redshift (z 0.9) a resolution of ∼10 arcmin and ∼500 deg2 would be necessary - something which would be difficult to achieve cheaply using a single dish. Continuum foreground emission from the Galaxy and extragalactic radio sources are potentially a problem. In particular, we suggest that it could be that the dominant extragalactic foreground comes from the clustering of very weak sources. We assess its amplitude and discuss ways by which it might be mitigated. We then introduce our concept for a dedicated single dish telescope designed to detect BAO at low redshifts. It involves an underillumintated static ∼40 m dish and a ∼60 element receiver array held ∼90 m above the underilluminated dish. Correlation receivers will be used with each main science beam referenced against an antenna pointing at one of the celestial poles for stability and control of systematics. We make sensitivity estimates for our proposed system and projections for the uncertainties on the power spectrum after 1 year of observations. We find that it is possible to measure the acoustic scale at z 0.3 with an accuracy ∼2.4 per cent and that w can be measured to an accuracy of 16 per cent.
We investigate the feasibility of measuring weak gravitational lensing using 21-cm intensity mapping with special emphasis on the performance of the planned Square Kilometre Array (SKA). We find that ...the current design for SKA_Mid should be able to measure the evolution of the lensing power spectrum at z ∼ 2–3 using this technique. This will be a probe of the expansion history of the Universe and gravity at a unique range in redshift. The signal to noise is found to be highly dependent on evolution of the neutral hydrogen fraction in the Universe with a higher H i density resulting in stronger signal. With realistic models for this, SKA Phase 1 should be capable of measuring the lensing power spectrum and its evolution. The dependence of signal to noise on the area and diameter of the array is quantified. We further demonstrate the applications of this technique by applying it to two specific coupled dark energy models that would be difficult to observationally distinguish without information from this range of redshift. We also investigate measuring the lensing signal with 21 cm emission from the Epoch of Reionization (EoR) using SKA and find that it is unlikely to constrain cosmological parameters because of the small survey size, but could provide a map of the dark matter within a small region of the sky.
Upcoming surveys will map the growth of large-scale structure with unprecented precision, improving our understanding of the dark sector of the Universe. Unfortunately, much of the cosmological ...information is encoded on small scales, where the clustering of dark matter and the effects of astrophysical feedback processes are not fully understood. This can bias the estimates of cosmological parameters, which we study here for a joint analysis of mock
Euclid
cosmic shear and
Planck
cosmic microwave background data. We use different implementations for the modelling of the signal on small scales and find that they result in significantly different predictions. Moreover, the different non-linear corrections lead to biased parameter estimates, especially when the analysis is extended into the highly non-linear regime, with the Hubble constant,
H
0
, and the clustering amplitude,
σ
8
, affected the most. Improvements in the modelling of non-linear scales will therefore be needed if we are to resolve the current tension with more and better data. For a given prescription for the non-linear power spectrum, using different corrections for baryon physics does not significantly impact the precision of
Euclid
, but neglecting these correction does lead to large biases in the cosmological parameters. In order to extract precise and unbiased constraints on cosmological parameters from
Euclid
cosmic shear data, it is therefore essential to improve the accuracy of the recipes that account for non-linear structure formation, as well as the modelling of the impact of astrophysical processes that redistribute the baryons.
In recent years, forecasting activities have become an important tool in designing and optimising large-scale structure surveys. To predict the performance of such surveys, the Fisher matrix ...formalism is frequently used as a fast and easy way to compute constraints on cosmological parameters. Among them lies the study of the properties of dark energy which is one of the main goals in modern cosmology. As so, a metric for the power of a survey to constrain dark energy is provided by the figure of merit (FoM). This is defined as the inverse of the surface contour given by the joint variance of the dark energy equation of state parameters { w 0 , w a } in the Chevallier-Polarski-Linder parameterization, which can be evaluated from the covariance matrix of the parameters. This covariance matrix is obtained as the inverse of the Fisher matrix. The inversion of an ill-conditioned matrix can result in large errors on the covariance coefficients if the elements of the Fisher matrix are estimated with insufficient precision. The conditioning number is a metric providing a mathematical lower limit to the required precision for a reliable inversion, but it is often too stringent in practice for Fisher matrices with sizes greater than 2 × 2. In this paper, we propose a general numerical method to guarantee a certain precision on the inferred constraints, such as the FoM. It consists of randomly vibrating (perturbing) the Fisher matrix elements with Gaussian perturbations of a given amplitude and then evaluating the maximum amplitude that keeps the FoM within the chosen precision. The steps used in the numerical derivatives and integrals involved in the calculation of the Fisher matrix elements can then be chosen accordingly in order to keep the precision of the Fisher matrix elements below this maximum amplitude. We illustrate our approach by forecasting stage IV spectroscopic surveys cosmological constraints from the galaxy power spectrum. We infer the range of steps for which the Fisher matrix approach is numerically reliable. We explicitly check that using steps that are larger by a factor of two produce an inaccurate estimation of the constraints. We further validate our approach by comparing the Fisher matrix contours to those obtained with a Monte Carlo Markov chain (MCMC) approach – in the case where the MCMC posterior distribution is close to a Gaussian – and finding excellent agreement between the two approaches.
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