likelihood-free inference in cosmology

At group meeting, MJ Vakili told us about his project with Chang Hoon Hahn (NYU) to do cosmological large-scale structure inferences using likelihood-free inference (ABC). We talked about the technical details, but also the philosophy: Current large-scale structure inferences generally use a substitute or made-up likelihood function that can't be correct: It is a Gaussian in correlation-function space. We can make fewer assumptions using ABC; indeed we can get correct posteriors without ever committing to the exact form of the likelihood function. We are performing the demonstration project with just the halo occupation distribution parameters, because this inference is cheaper than the full cosmological inference.