Constraining Modified Gravity and Growth with Weak Lensing

Abstract

The idea that we live in a Universe undergoing a period of acceleration is a strongly held notion in cosmology. As this can, potentially, be explained with a modification to General Relativity we look at current cosmological data with the purpose of testing aspects of gravity. Firstly we constrain a phenomenological model (mDGP) motivated by a possible extra dimension. This is characterised by $\alpha$ which interpolates between (LCDM) and (the Dvali Gabadadze Porrati (DGP) model). In addition, we analyse general signatures of modified gravity given by the growth parameter $\gamma$ and power spectrum parameter $\Sigma$. We utilise Weak Lensing data (CFHTLS-wide) in combination with Baryon Acoustic Oscillations (BAOs) and Supernovae data. We show that current weak lensing data is not yet capable of constraining either model in isolation. However we demonstrate that this probe is highly beneficial, for in combination with BAOs and Supernovae we obtain $\alpha <0.58$ and $\alpha <0.91$ at $1\sigma$ and $2\sigma$, respectively. Without the lensing data no constraint is possible. Both analyses disfavour the flat DGP braneworld model ($\alpha =1$) at over $2\sigma$. We highlight these are insensitive to potential systematics in the lensing data. For the growth signature $\gamma$ we show that, in combination, these probes do not yet have sufficient constraining power. Finally, we look beyond these present capabilities and demonstrate that Euclid, a future weak lensing survey, will deeply probe the nature of gravity. A $1\sigma$ error of 0.104 is found for $\alpha$ ($l_{max}=500$) whereas for the general modified signatures we forecast $1\sigma$ errors of 0.045 for $\gamma$ and 0.25 for ${\Sigma }_0$ ($l_{max}=500$), which is further tightened to 0.038 for $\gamma$ and 0.069 for ${\Sigma }_0$ ($l_{max}=10000$).

15 pages, 9 figures

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• New Gravitational Scales in Cosmological Surveys
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• Weak lensing predictions for modified gravities at non-linear scales
• Time evolution of intrinsic alignments of galaxies
• Parametrized modified gravity constraints after Planck
• Figures of merit and constraints from testing General Relativity using the latest cosmological data sets including refined COSMOS 3D weak lensing
• COSMOS weak-lensing constraints on modified gravity
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• Effects of Dark Energy Perturbations on Cosmological Tests of General Relativity
• The Angular Power Spectra of Photometric SDSS LRGs
• Exploring degeneracies in modified gravity with weak lensing
• Testing gravity with $E_G$: mapping theory onto observations
• Self-Calibration Technique for 3-point Intrinsic Alignment Correlations in Weak Lensing Surveys
• Self-Calibration for 3-point Intrinsic Alignment Auto-Correlations in Weak Lensing Surveys
• Model-Independent Reconstruction of the Expansion History of the Universe from Type Ia Supernovae
• The $\Lambda$CDM growth rate of structure revisited
• Disentangling dark energy and cosmic tests of gravity from weak lensing systematics
• Modified Gravity: the CMB, Weak Lensing and General Parameterisations
• Calibrating photometric redshift distributions with cross-correlations
• Tomography from the Next Generation of Cosmic Shear Experiments for Viable f(R) Models
• Model Independent Tests of Cosmic Gravity
• Reconstructing Cosmological Matter Perturbations using Standard Candles and Rulers
• Weak lensing probe of cubic Galileon model
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• Testing a Phenomenologically Extended DGP Model with Upcoming Weak Lensing Surveys
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• Testing Dvali-Gabadadze-Porrati Gravity with Planck
• New measures to test modified gravity cosmologies
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