Cosmological observations indicate that there is insufficient baryonic matter in the Universe for the correct description of physical processes, if the law of gravity is dictated by General Relativity. A natural explanation is that most of the matter fields interact negligibly with light, and are thus called Dark Matter, but can still be seen through their gravitational effect. Determining the nature of Dark Matter is one of the foremost problems of modern cosmology. Dark Matter is generally thought to be a stable particle (or particles) not part of the standard model and although it has so far remained elusive, the next generation of cosmological observations offer a fantastic opportunity for revealing a great deal about its properties.
As a PhD student, you will work on studying various aspects of Dark Matter phenomenology with cosmology. Possibilities include investigations of the formation of cosmic structure using effective field theory  and/or numerical techniques [2,3], investigation of the effects of various dark matter models (such as ultralight axions) on cosmological observables  and models involving gravity beyond General Relativity.