Constraining beyond LCDM models with stage-IV dark energy surveys

Cosmology has entered an era of “Stage-IV” dark energy surveys. With the stage IV surveys, we can go beyond constraining the dark energy equation of state. We have demonstrated that it is indeed possible to test general relativity itself by combining various cosmology measurements achieved by these surveys. The major limitation currently in testing gravity using cosmological observations is that we need to throw away all the information on nonlinear scales. For example, in the Dark Energy Survey photometric analysis, only 55% of the data points were used to test gravity compared with the fiducial analysis in ΛCDM as only the data points on linear scales could be used. In addition, the gravitational effects on matter are often obtained by using constraints on the growth rate from spectroscopic redshift distortions. These constraints are obtained assuming nonlinear modelling in ΛCDM and care needs to be taken when using them in beyond-ΛCDM models. This project will provide methodologies and tools to exploit the information available on nonlinear scales to test general relativity on cosmological scales.