David J. Bacon

Publications (5)0 Total impact

• Source

  Available from: Marco Baldi

  Article: Weak lensing predictions for coupled dark energy cosmologies at non-linear scales

  Emma Beynon, Marco Baldi, David J. Bacon, Kazuya Koyama, Cristiano Sabiu
  [show abstract] [hide abstract]
  ABSTRACT: We present non-linear weak lensing predictions for coupled dark energy models using the CoDECS simulations. We calculate the shear correlation function and error covariance expected for these models, for forthcoming ground-based (such as DES) and space-based (Euclid) weak lensing surveys. We obtain predictions for the discriminatory power of a ground-based survey similar to DES and a space-based survey such as Euclid in distinguishing between $\Lambda$CDM and coupled dark energy models; we show that using the non-linear lensing signal we could discriminate between $\Lambda$CDM and exponential constant coupling models with $\beta_0\geq0.1$ at $4\sigma$ confidence level with a DES-like survey, and $\beta_0\geq0.05$ at $5\sigma$ confidence level with Euclid. We also demonstrate that estimating the coupled dark energy models' non-linear power spectrum, using the $\Lambda$CDM Halofit fitting formula, results in biases in the shear correlation function that exceed the survey errors.
  11/2011;
• Source

  Available from: ArXiv

  Article: Testing Einstein gravity with cosmic growth and expansion

  Gong-Bo Zhao, Hong Li, Eric V. Linder, Kazuya Koyama, David J. Bacon, Xinmin Zhang
  [show abstract] [hide abstract]
  ABSTRACT: We test Einstein gravity using cosmological observations of both expansion and structure growth, including the latest data from supernovae (Union2.1), cosmic microwave background (WMAP7), weak lensing (CFHTLS) and the peculiar velocity of galaxies (WiggleZ). We fit modified gravity parameters of the generalized Poisson equations simultaneously with the effective equation of state for the background evolution, exploring the covariances and model dependence. The results show that general relativity is a good fit to the combined data. Using a Padé approximant form for the gravity deviations accurately captures the time and scale dependence for theories like f(R) and DGP gravity, and weights high and low redshift probes fairly. For current observations, cosmic growth and expansion can be fit simultaneously with little degradation in accuracy, while removing the possibility of bias from holding one aspect fixed.
  Phys. Rev. D. 09/2011; 85(12).
• Source

  Available from: Mario G. Santos

  Article: Cosmological Measurements with Forthcoming Radio Continuum Surveys

  Alvise Raccanelli, Gong-Bo Zhao, David J. Bacon, Matt J. Jarvis, Will J. Percival, Ray P. Norris, Huub Rottgering, Filipe B. Abdalla, Catherine M. Cress, Jean-Claude Kubwimana, Sam Lindsay, Robert C. Nichol, Mario G. Santos, Dominik J. Schwarz
  [show abstract] [hide abstract]
  ABSTRACT: We present forecasts for constraints on cosmological models which can be obtained by forthcoming radio continuum surveys: the wide surveys with the LOw Frequency ARray (LOFAR), Australian Square Kilometre Array Pathfinder (ASKAP) and the Westerbork Observations of the Deep APERTIF Northern sky (WODAN). We use simulated catalogues appropriate to the planned surveys to predict measurements obtained with the source auto-correlation, the cross-correlation between radio sources and CMB maps (the Integrated Sachs-Wolfe effect), the cross-correlation of radio sources with foreground objects due to cosmic magnification, and a joint analysis together with the CMB power spectrum and supernovae. We show that near future radio surveys will bring complementary measurements to other experiments, probing different cosmological volumes, and having different systematics. Our results show that the unprecedented sky coverage of these surveys combined should provide the most significant measurement yet of the Integrated Sachs-Wolfe effect. In addition, we show that using the ISW effect will significantly tighten constraints on modified gravity parameters, while the best measurements of dark energy models will come from galaxy auto-correlation function analyses. Using the combination of EMU and WODAN to provide a full sky survey, it will be possible to measure the dark energy parameters with an uncertainty of \{$\sigma (w_0) = 0.05$, $\sigma (w_a) = 0.12$\} and the modified gravity parameters \{$\sigma (\eta_0) = 0.10$, $\sigma (\mu_0) = 0.05$\}, assuming Planck CMB+SN(current data) priors. Finally, we show that radio surveys would detect a primordial non-Gaussianity of $f_{\rm NL}$ = 8 at 1-$\sigma$ and we briefly discuss other promising probes.
  08/2011;
• Source

  Available from: Alessandra Silvestri

  Article: Probing modifications of General Relativity using current cosmological observations

  Gong-Bo Zhao, Tommaso Giannantonio, Levon Pogosian, Alessandra Silvestri, David J. Bacon, Kazuya Koyama, Robert C. Nichol, Yong-Seon Song
  [show abstract] [hide abstract]
  ABSTRACT: We test General Relativity (GR) using current cosmological data: the cosmic microwave background (CMB) from WMAP5 (Komatsu et al. 2009), the integrated Sachs-Wolfe (ISW) effect from the cross-correlation of the CMB with six galaxy catalogs (Giannantonio et al. 2008), a compilation of supernovae Type Ia (SNe) including the latest SDSS SNe (Kessler et al. 2009), and part of the weak lensing (WL) data from CFHTLS (Fu et al. 2008, Kilbinger et al. 2009) that probe linear and mildly non-linear scales. We first test a model where the effective Newton's constant, mu, and the ratio of the two gravitational potentials, eta, transit from the GR value to another constant at late times; in this case, we find that standard GR is fully consistent with the combined data. The strongest constraint comes from the ISW effect which would arise from this gravitational transition; the observed ISW signal imposes a tight constraint on a combination of mu and eta that characterizes the lensing potential. Next, we consider four pixels in time and space for each function mu and eta, and perform a Principal Component Analysis (PCA) finding that seven of the resulting eight eigenmodes are consistent with GR within the errors. Only one eigenmode shows a 2-sigma deviation from the GR prediction, which is likely to be due to a systematic effect. However, the detection of such a deviation demonstrates the power of our time- and scale-dependent PCA methodology when combining observations of structure formation and expansion history to test GR. Comment: 14 pages, 10 figures. Minor modifications, version published by Phys. Rev. D
  03/2010;
• Source

  Available from: ArXiv

  Article: Weak lensing predictions for modified gravities at non-linear scales

  Emma Beynon, David J. Bacon, Kazuya Koyama
  [show abstract] [hide abstract]
  ABSTRACT: We present a set of predictions for weak lensing correlation functions in the context of modified gravity models, including a prescription for the impact of the nonlinear power spectrum regime in these models. We consider the DGP and f(R) models, together with dark energy models with the same expansion history. We use the requirement that gravity is close to GR on small scales to estimate the non-linear power for these models. We then calculate weak lensing statistics, showing their behaviour as a function of scale and redshift, and present predictions for measurement accuracy with future lensing surveys, taking into account cosmic variance and galaxy shape noise. We demonstrate the improved discriminatory power of weak lensing for testing modified gravities once the nonlinear power spectrum contribution has been included. We also examine the ability of future lensing surveys to constrain a parameterisation of the non-linear power spectrum, including sensitivity to the growth factor. Comment: 10 pages, 9 figures, 6 tables; v2: updated references; v3: accepted for publication in MNRAS
  10/2009;