Institution
Institute of Cosmology and Gravitation, University of Portsmouth
About: Institute of Cosmology and Gravitation, University of Portsmouth is a based out in . It is known for research contribution in the topics: Galaxy & Redshift. The organization has 297 authors who have published 1207 publications receiving 76919 citations.
Topics: Galaxy, Redshift, Dark energy, Dark matter, Cosmic microwave background
Papers published on a yearly basis
Papers
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TL;DR: In this article, a hierarchy of diffusion equations is derived, the solutions of which yield moments of the numbers of inflationary $e$-folds, which can be used to calculate the distribution of primordial density perturbations in the stochastic-$\delta N$ formalism.
Abstract: Stochastic effects in multi-field inflationary scenarios are investigated. A hierarchy of diffusion equations is derived, the solutions of which yield moments of the numbers of inflationary $e$-folds. Solving the resulting partial differential equations in multi-dimensional field space is more challenging than the single-field case. A few tractable examples are discussed, which show that the number of fields is, in general, a critical parameter. When more than two fields are present for instance, the probability to explore arbitrarily large-field regions of the potential, otherwise inaccessible to single-field dynamics, becomes non-zero. In some configurations, this gives rise to an infinite mean number of $e$-folds, regardless of the initial conditions. Another difference with respect to single-field scenarios is that multi-field stochastic effects can be large even at sub-Planckian energy. This opens interesting new possibilities for probing quantum effects in inflationary dynamics, since the moments of the numbers of $e$-folds can be used to calculate the distribution of primordial density perturbations in the stochastic-$\delta N$ formalism.
48 citations
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TL;DR: In this article, the authors find that recent CMB data seem to favor a contribution of a primordial isocurvature mode where the entropy perturbation is positively correlated with the primordial curvature perturbations and has a large spectral index (niso ~ 3).
Abstract: The improved data on the cosmic microwave background (CMB) anisotropy allow a better determination of the adiabaticity of the primordial perturbation. Interestingly, we find that recent CMB data seem to favor a contribution of a primordial isocurvature mode where the entropy perturbation is positively correlated with the primordial curvature perturbation and has a large spectral index (niso ~ 3). With four additional parameters we obtain a better fit to the CMB data by Δχ2 = 9.7 compared to an adiabatic model. For this best-fit model the non-adiabatic contribution to the CMB temperature variance is 4%. According to a Markov chain Monte Carlo analysis the non-adiabatic contribution is positive at more than 95% confidence level. The exact confidence level depends somewhat on the choice of priors, and we discuss the effect of different priors as well as additional cosmological data.
48 citations
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Ludwig Maximilian University of Munich1, Max Planck Society2, IFAE3, University of Pennsylvania4, Stanford University5, SLAC National Accelerator Laboratory6, Fermilab7, Institute of Cosmology and Gravitation, University of Portsmouth8, Carnegie Institution for Science9, Institut d'Astrophysique de Paris10, University College London11, National Center for Supercomputing Applications12, University of Illinois at Urbana–Champaign13, Texas A&M University14, Indian Institute of Technology, Hyderabad15, University of Michigan16, Spanish National Research Council17, University of Chicago18, Autonomous University of Madrid19, University of Cambridge20, ETH Zurich21, Santa Cruz Institute for Particle Physics22, Ohio State University23, Harvard University24, Australian Astronomical Observatory25, University of São Paulo26, Princeton University27, Catalan Institution for Research and Advanced Studies28, California Institute of Technology29, University of Sussex30, University of Southampton31, Brandeis University32, State University of Campinas33, Oak Ridge National Laboratory34
TL;DR: In this article, the relative bias between galaxies and galaxy clusters that are located inside and in the vicinity of cosmic voids, extended regions of relatively low density in the large-scale structure of the Universe, was investigated.
Abstract: Luminous tracers of large-scale structure are not entirely representative of the distribution of mass in our Universe. As they arise from the highest peaks in the matter density field, the spatial distribution of luminous objects is biased towards those peaks. On large scales, where density fluctuations are mild, this bias simply amounts to a constant offset in the clustering amplitude of the tracer, known as linear bias. In this work we focus on the relative bias between galaxies and galaxy clusters that are located inside and in the vicinity of cosmic voids, extended regions of relatively low density in the large-scale structure of the Universe. With the help of mock data we verify that the relation between galaxy and cluster overdensity around voids remains linear. Hence, the void-centric density profiles of different tracers can be linked by a single multiplicative constant. This amounts to the same value as the relative linear bias between tracers for the largest voids in the sample. For voids of small sizes, which typically arise in higher density regions, this constant has a higher value, possibly showing an environmental dependence similar to that observed for the linear bias itself. We confirm our findings by analysing data obtained during the first year of observations by the Dark Energy Survey. As a side product, we present the first catalogue of three-dimensional voids extracted from a photometric survey with a controlled photo-z uncertainty. Our results will be relevant in forthcoming analyses that attempt to use voids as cosmological probes.
47 citations
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TL;DR: In this paper, the authors present a public catalogue of voids in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 11 LOWZ and CMASS galaxy surveys, which contains information on the location, sizes, densities, shapes and bounding surfaces of 8956 independent disjoint voids.
Abstract: We present a public catalogue of voids in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 11 LOWZ and CMASS galaxy surveys. This catalogue contains information on the location, sizes, densities, shapes and bounding surfaces of 8956 independent, disjoint voids, making it the largest public void catalogue to date. Voids are identied using a version of the ZOBOV algorithm, the operation of which has been calibrated through tests on mock galaxy populations inN-body simulations, as well as on a suite of 4096 mock catalogues which fully reproduce the galaxy clustering, survey masks and selection functions. Based on this, we estimate a false positive detection rate of 3%. Comparison with mock catalogues limits deviations of the void size distribution from that predicted in the CDM model to be less than 6% for voids with eective radius 8 < Rv < 60h 1 Mpc and in the redshift range 0:15 < z < 0:7. This could tightly constrain modied gravity scenarios and models with a varying equation of state, but we identify systematic biases which must be accounted for to reduce the theoretical uncertainty in the predictions for these models to the current level of precision attained from the data. We also examine the distribution of void densities and identify a decit of the deepest voids relative to CDM expectations, which is signicant at more than the 3 equivalent level. We discuss possible explanations for this discrepancy but at present its cause remains unknown.
47 citations
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University of Cambridge1, Spanish National Research Council2, University of Michigan3, Fermilab4, University of Arizona5, California Institute of Technology6, University of Chicago7, Stanford University8, University of Hawaii9, Ohio State University10, Argonne National Laboratory11, University of Wisconsin-Madison12, University of Pennsylvania13, SLAC National Accelerator Laboratory14, Carnegie Mellon University15, University of La Laguna16, University of Illinois at Urbana–Champaign17, National Center for Supercomputing Applications18, University of Manchester19, Santa Cruz Institute for Particle Physics20, University of California, Berkeley21, University College London22, IFAE23, University of Geneva24, Brookhaven National Laboratory25, Duke University26, University of São Paulo27, Autonomous University of Madrid28, Institute of Cosmology and Gravitation, University of Portsmouth29, Institut d'Astrophysique de Paris30, University of Sussex31, INAF32, Indian Institute of Technology, Hyderabad33, University of Oslo34, University of Queensland35, Smithsonian Institution36, Macquarie University37, Lowell Observatory38, Catalan Institution for Research and Advanced Studies39, Princeton University40, University of Southampton41, Oak Ridge National Laboratory42, Max Planck Society43, Ludwig Maximilian University of Munich44
TL;DR: In this article, a fiducial covariance matrix model for the combined 2-point function analysis of the Dark Energy Survey Year 3 (DES-Y3) dataset is presented.
Abstract: We describe and test the fiducial covariance matrix model for the combined 2-point function analysis of the Dark Energy Survey Year 3 (DES-Y3) dataset. Using a variety of new ansatzes for covariance modelling and testing we validate the assumptions and approximations of this model. These include the assumption of a Gaussian likelihood, the trispectrum contribution to the covariance, the impact of evaluating the model at a wrong set of parameters, the impact of masking and survey geometry, deviations from Poissonian shot-noise, galaxy weighting schemes and other, sub-dominant effects. We find that our covariance model is robust and that its approximations have little impact on goodness-of-fit and parameter estimation. The largest impact on best-fit figure-of-merit arises from the so-called $f_{\mathrm{sky}}$ approximation for dealing with finite survey area, which on average increases the $\chi^2$ between maximum posterior model and measurement by $3.7\%$ ($\Delta \chi^2 \approx 18.9$). Standard methods to go beyond this approximation fail for DES-Y3, but we derive an approximate scheme to deal with these features. For parameter estimation, our ignorance of the exact parameters at which to evaluate our covariance model causes the dominant effect. We find that it increases the scatter of maximum posterior values for $\Omega_m$ and $\sigma_8$ by about $3\%$ and for the dark energy equation of state parameter by about $5\%$.
47 citations
Authors
Showing all 297 results
Name | H-index | Papers | Citations |
---|---|---|---|
Robert C. Nichol | 187 | 851 | 162994 |
Daniel Thomas | 134 | 846 | 84224 |
Will J. Percival | 129 | 473 | 87752 |
Tommaso Treu | 126 | 715 | 49090 |
Claudia Maraston | 103 | 362 | 59178 |
Marco Cavaglia | 93 | 372 | 60157 |
Ashley J. Ross | 90 | 248 | 46395 |
David A. Wake | 89 | 214 | 46124 |
László Á. Gergely | 89 | 426 | 60674 |
L. K. Nuttall | 89 | 253 | 54834 |
Rita Tojeiro | 87 | 229 | 43140 |
Roy Maartens | 86 | 432 | 23747 |
David Keitel | 85 | 253 | 56849 |
Davide Pietrobon | 83 | 152 | 62010 |
Gong-Bo Zhao | 81 | 287 | 35540 |