Tests of modified gravity

The observation of accelerated expansion is one of the most important discoveries in modern cosmology. But although these observations are now supported by a large number of experiments, we remain entirely ignorant of the underlying microphysics. 'Modified' gravities are a class of models which propose that the acceleration is explained by changing the gravitational force law or the number of degrees of freedom in the gravitational sector. Both possibilities can be tested by measurements of cosmological structure formation.

 The theoretical position of modified gravity is very uncertain, with models developing at a rapid rate. Frameworks for testing them have developed much less rapidly. Projects available in this area include: (1) understanding how to develop tests for modified gravity which respect the (sometimes very delicate) theoretical conditions for consistency of models, (2) finding ways to disentangle changes to the initial conditions of structure formation from changes to its dynamics (that is, the forces which operate during assembly of structure), (3) understanding how to combine multiple measurements (for example, redshift space distortions, weak lensing surveys) to constrain different types of model.

Projects in this area typically requires a mix of analytical and numerical work. A background in relativity, cosmology and quantum field theory is helpful.