Antony Lewis

University of Sussex

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A. Challinor

University of Cambridge

M. Remazeilles

University of Manchester

F. R. Bouchet

Sorbonne Université

A. Lasenby

University of Cambridge

M. Tomasi

University of Milan

E. Hivon

Centre National de la Recherche Scientifique

G. de Zotti

Osservatorio Astronomico di Padova

G. Polenta

Agenzia Spaziale Italiana

C. Burigana

Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

M. Liguori

University of Padua

Cooperative Institutions

Centre National de la Recherche Scientifique

481

University of California, Berkeley

235

Université Paris Cité

212

California Institute of Technology

203

Princeton University

159

Université Paris-Saclay

158

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

144

University of Chicago

144

University of Cambridge

139

Sorbonne Paris Cité

139

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Cosmological parameters from CMB and other data: A Monte Carlo approach

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (2002)

Antony Lewis Sarah Bridle

We present a fast Markov chain Monte Carlo exploration of cosmological parameter space. We perform a joint analysis of results from recent cosmic microwave background (CMB) experiments and provide parameter constraints, including ${\ensuremath{\sigma}}_{8},$ from the CMB independent of other data. We next combine data from the CMB, HST Key Project, 2dF galaxy redshift survey, supernovae type Ia and big-bang nucleosynthesis. The Monte Carlo method allows the rapid investigation of a large number of parameters, and we present results from 6 and 9 parameter analyses of flat models, and an 11 parameter analysis of non-flat models. Our results include constraints on the neutrino mass ${(m}_{\ensuremath{\nu}}\ensuremath{\lesssim}0.3\mathrm{eV}),$ equation of state of the dark energy, and the tensor amplitude, as well as demonstrating the effect of additional parameters on the base parameter constraints. In a series of appendixes we describe the many uses of importance sampling, including computing results from new data and accuracy correction of results generated from an approximate method. We also discuss the different ways of converting parameter samples to parameter constraints, the effect of the prior, assess the goodness of fit and consistency, and describe the use of analytic marginalization over normalization parameters.

Big Bang nucleosynthesis

10.1103/physrevd.66.103511

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Citations (3,179)

Implementing CAMAC-computer systems

I.N. Hooton Antony Lewis N.P. Whitehead

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Planck2018 results

Astronomy and Astrophysics (2019)

Y. Akrami F. Arroja M. Ashdown J. Aumont C. Baccigalupi

We report on the implications for cosmic inflation of the 2018 Release of the Planck CMB anisotropy measurements. The results are fully consistent with the two previous Planck cosmological releases, but have smaller uncertainties thanks to improvements in the characterization of polarization at low and high multipoles. Planck temperature, polarization, and lensing data determine the spectral index of scalar perturbations to be $n_\mathrm{s}=0.9649\pm 0.0042$ at 68% CL and show no evidence for a scale dependence of $n_\mathrm{s}.$ Spatial flatness is confirmed at a precision of 0.4% at 95% CL with the combination with BAO data. The Planck 95% CL upper limit on the tensor-to-scalar ratio, $r_{0.002}<0.10$, is further tightened by combining with the BICEP2/Keck Array BK15 data to obtain $r_{0.002}<0.056$. In the framework of single-field inflationary models with Einstein gravity, these results imply that: (a) slow-roll models with a concave potential, $V" (\phi) < 0,$ are increasingly favoured by the data; and (b) two different methods for reconstructing the inflaton potential find no evidence for dynamics beyond slow roll. Non-parametric reconstructions of the primordial power spectrum consistently confirm a pure power law. A complementary analysis also finds no evidence for theoretically motivated parameterized features in the Planck power spectrum, a result further strengthened for certain oscillatory models by a new combined analysis that includes Planck bispectrum data. The new Planck polarization data provide a stringent test of the adiabaticity of the initial conditions. The polarization data also provide improved constraints on inflationary models that predict a small statistically anisotropic quadrupolar modulation of the primordial fluctuations. However, the polarization data do not confirm physical models for a scale-dependent dipolar modulation.

10.1051/0004-6361/201833887

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Citations (1,793)

Planck2013 results. I. Overview of products and scientific results

Astronomy and Astrophysics (2014)

P. A. R. Ade N. Aghanim M. I. R. Alves C. Armitage-Caplan M. Arnaud

The ESA's Planck satellite, dedicated to studying the early Universe and its subsequent evolution, was launched 14 May 2009 and has been scanning the microwave and submillimetre sky continuously since 12 August 2009. This paper gives an overview of the mission and its performance, the processing, analysis, and characteristics of the data, the scientific results, and the science data products and papers in the release. The science products include maps of the CMB and diffuse extragalactic foregrounds, a catalogue of compact Galactic and extragalactic sources, and a list of sources detected through the SZ effect. The likelihood code used to assess cosmological models against the Planck data and a lensing likelihood are described. Scientific results include robust support for the standard six-parameter LCDM model of cosmology and improved measurements of its parameters, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for these parameters and others derived from them are significantly different from those previously determined. Several large-scale anomalies in the temperature distribution of the CMB, first detected by WMAP, are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at greater than 25 sigma. Planck finds no evidence for non-Gaussianity in the CMB. Planck's results agree well with results from the measurements of baryon acoustic oscillations. Planck finds a lower Hubble constant than found in some more local measures. Some tension is also present between the amplitude of matter fluctuations derived from CMB data and that derived from SZ data. The Planck and WMAP power spectra are offset from each other by an average level of about 2% around the first acoustic peak.

CMB cold spot

Sunyaev–Zel'dovich effect

Planck energy

10.1051/0004-6361/201321529

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Citations (1,490)

The real shape of non-Gaussianities

Journal of Cosmology and Astroparticle Physics (2011)

Antony Lewis

I review what bispectra and trispectra look like in real space, in terms of the sign of particular shaped triangles and tetrahedrons. Having an equilateral density bispectrum of positive sign corresponds to having concentrated overdensities surrounded by larger weaker underdensities. In 3D these are concentrated density filaments, as expected in large-scale structure. As the shape changes from equilateral to flattened the concentrated overdensities flatten into lines (3D planes). I then focus on squeezed bispectra, which can be thought of as correlations of changes in small-scale power with large-scale fields, and discuss the general non-perturbative form of the squeezed bispectrum and its angular dependence. A general trispectrum has tetrahedral form and I show examples of what this can look like in real space. Squeezed trispectra are of particular interest and come in two forms, corresponding to large-scale variance of small-scale power, and correlated modulations of an equilateral-form bispectrum. Flattened trispectra can be produced by line-like features in 2D, for example from cosmic strings, and randomly located features also give a non-Gaussian signal. There are relationships between the squeezed types of non-Gaussianity, and also a useful interpretation in terms of statistical anisotropy. I discuss the various possible physical origins of cosmological non-Gaussianities, both in terms of primordial perturbations and late-time dynamical and geometric effects.

Trispectrum

Equilateral triangle

10.1088/1475-7516/2011/10/026

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Citations (64)

Planck intermediate results - XLVII. Planck constraints on reionization history

Institutional Repository of the University of Granada (University of Granada) (2016)

R. Adam N. Aghanim M. Ashdown J. Aumont C. Baccigalupi

We investigate constraints on cosmic reionization extracted from the Planck cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy data in temperature with the low-multipole polarization data to fit ΛCDM models with various parameterizations of the reionization history. We obtain a Thomson optical depth τ = 0.058 ± 0.012 for the commonly adopted instantaneous reionization model. This confirms, with data solely from CMB anisotropies, the low value suggested by combining Planck 2015 results with other data sets, and also reduces the uncertainties. We reconstruct the history of the ionization fraction using either a symmetric or an asymmetric model for the transition between the neutral and ionized phases. To determine better constraints on the duration of the reionization process, we also make use of measurements of the amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional information from the high-resolution Atacama Cosmology Telescope and South Pole Telescope experiments. The average redshift at which reionization occurs is found to lie between z = 7.8 and 8.8, depending on the model of reionization adopted. Using kSZ constraints and a redshift-symmetric reionization model, we find an upper limit to the width of the reionization period of Δz < 2.8. In all cases, we find that the Universe is ionized at less than the 10% level at redshifts above z ≃ 10. This suggests that an early onset of reionization is strongly disfavoured by the Planck data. We show that this result also reduces the tension between CMB-based analyses and constraints from other astrophysical sources.

South Pole Telescope

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Citations (300)

Planck intermediate results. XLVII. Planck constraints on reionization history

Institutional Repository of the University of Granada (University of Granada) (2016)

R. Adam N. Aghanim M. Ashdown J. Aumont C. Baccigalupi

We investigate constraints on cosmic reionization extracted from the Planck cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy data in temperature with the low-multipole polarization data to fit LCDM models with various parameterizations of the reionization history. We obtain a Thomson optical depth tau=0.058 +/- 0.012 for the commonly adopted instantaneous reionization model. This confirms, with only data from CMB anisotropies, the low value suggested by combining Planck 2015 results with other data sets and also reduces the uncertainties. We reconstruct the history of the ionization fraction using either a symmetric or an asymmetric model for the transition between the neutral and ionized phases. To determine better constraints on the duration of the reionization process, we also make use of measurements of the amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional information from the high resolution Atacama Cosmology Telescope and South Pole Telescope experiments. The average redshift at which reionization occurs is found to lie between z=7.8 and 8.8, depending on the model of reionization adopted. Using kSZ constraints and a redshift-symmetric reionization model, we find an upper limit to the width of the reionization period of Dz < 2.8. In all cases, we find that the Universe is ionized at less than the 10% level at redshifts above z~10. This suggests that an early onset of reionization is strongly disfavoured by the Planck data. We show that this result also reduces the tension between CMB-based analyses and constraints from other astrophysical sources.

South Pole Telescope

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Citations (329)

Planckintermediate results

Astronomy and Astrophysics (2016)

R. Adam N. Aghanim M. Ashdown J. Aumont C. Baccigalupi

We investigate constraints on cosmic reionization extracted from the Planck cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy data in temperature with the low-multipole polarization data to fit LCDM models with various parameterizations of the reionization history. We obtain a Thomson optical depth tau=0.058 +/- 0.012 for the commonly adopted instantaneous reionization model. This confirms, with only data from CMB anisotropies, the low value suggested by combining Planck 2015 results with other data sets and also reduces the uncertainties. We reconstruct the history of the ionization fraction using either a symmetric or an asymmetric model for the transition between the neutral and ionized phases. To determine better constraints on the duration of the reionization process, we also make use of measurements of the amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional information from the high resolution Atacama Cosmology Telescope and South Pole Telescope experiments. The average redshift at which reionization occurs is found to lie between z=7.8 and 8.8, depending on the model of reionization adopted. Using kSZ constraints and a redshift-symmetric reionization model, we find an upper limit to the width of the reionization period of Dz < 2.8. In all cases, we find that the Universe is ionized at less than the 10% level at redshifts above z~10. This suggests that an early onset of reionization is strongly disfavoured by the Planck data. We show that this result also reduces the tension between CMB-based analyses and constraints from other astrophysical sources.

South Pole Telescope

10.1051/0004-6361/201628897

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Citations (413)

Bayesian Methods in Cosmology

Cambridge University Press eBooks (2009)

M. P. Hobson M. P. Hobson John Skilling D. S. Sivia Antony Lewis

In recent years cosmologists have advanced from largely qualitative models of the Universe to precision modelling using Bayesian methods, in order to determine the properties of the Universe to high accuracy. This timely book is the only comprehensive introduction to the use of Bayesian methods in cosmological studies, and is an essential reference for graduate students and researchers in cosmology, astrophysics and applied statistics. The first part of the book focuses on methodology, setting the basic foundations and giving a detailed description of techniques. It covers topics including the estimation of parameters, Bayesian model comparison, and separation of signals. The second part explores a diverse range of applications, from the detection of astronomical sources (including through gravitational waves), to cosmic microwave background analysis and the quantification and classification of galaxy properties. Contributions from 24 highly regarded cosmologists and statisticians make this an authoritative guide to the subject.

10.1017/cbo9780511802461

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Citations (178)

Accuracy of cosmological parameters using the baryon acoustic scale

Journal of Cosmology and Astroparticle Physics (2015)

Kiattisak Thepsuriya Antony Lewis

Percent-level measurements of the comoving baryon acoustic scale standard ruler can be used to break degeneracies in parameter constraints from the CMB alone. The sound horizon at the epoch of baryon drag is often used as a proxy for the scale of the peak in the matter density correlation function, and can conveniently be calculated quickly for different cosmological models. However, the measurements are not directly constraining this scale, but rather a measurement of the full correlation function, which depends on the detailed evolution through decoupling. We assess the level of reliability of parameter constraints based on a simple approximation of the acoustic scale compared to a more direct determination from the full numerical two-point correlation function. Using a five-parameter fitting technique similar to recent BAO data analyses, we find that for standard {\Lambda}CDM models and extensions with massive neutrinos and additional relativistic degrees of freedom, the approximation is at better than 0.15% for most parameter combinations varying over reasonable ranges.

Baryon Acoustic Oscillations

Decoupling (probability)

10.1088/1475-7516/2015/01/034

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Citations (9)