Probing fundamental fields in strong gravity

AIM: Develop numerical relativity simulations and analytic models of black holes (BHs) and black hole binaries (BHBs) in dark matter environments, comparing and contrasting the high and low mass candidates, and identifying observational signatures for each case.

BACKGROUND: The 2015 detection of gravitational waves (GWs) by LIGO was a breakthrough moment for science. LIGO (and Virgo) are currently in their third observation run with over 30 new candidate events reported so far, and the next decade promises a deluge of new data detected by a world-wide network of GW instruments. It will also be a crucial stage in preparations for the LISA space based mission, which will expand our field of vision into frequencies which probe the rich DM environments of supermassive black holes (SMBHs) and background signals from the early universe (~ 10-4 - 10-1 Hz). To make sense of the data streams we will receive we need to fully understand the theoretical predictions that are made by current theories, such as General Relativity, including possible deviations relating to new physics.

One effect which is of particular interest is the impact of dark matter (DM) environments on BHs and their subsequent merger. Whilst DM composes a significant fraction of the energy budget of the Universe, so far the only confirmed interaction channel with other matter is via gravitational interactions. Studies of the behaviour of DM in strong gravity environments may therefore be the only way to understand the particle physics, for example, to distinguish high mass and low mass particles, and constrain self interactions. The deviations in GWs resulting from DM environments are expected to be small for BH inspiral and ringdown, but the merger phase is not well quantified, and the effects there may be enhanced in specific situations. Given the importance of the DM question, and ever-increasing detector sensitivity, such effects merit further investigation.

METHODS: The project will use analytic methods and recently developed numerical code to study low mass, bosonic dark matter environments for isolated BHs and BBHs. The project will also involve developing a fully general relativistic N-body code (as part of the GRChombo framework), to study the behaviour of heavy dark matter candidates in strongly curved spacetimes, permitting a direct comparison of the two mass cases which will allow us to discern potentially detectable signatures of each. Few such hybrid NR/N-body codes exist (to our knowledge, only one) and none are currently publicly available.

RELEVANCE TO STFC GOALS: The proposed project falls within the STFC Roadmap for Particle Astrophysics theme Fundamental Physics with Cosmic Messengers, in particular, it is relevant to the questions:
(2a) What is the nature of Dark Matter?
(2e) Are there particles present in the universe which have not yet been detected either directly or indirectly?

These in turn address the Science Challenges identified by STFC as core to its programme, namely:
(C) What are the fundamental constituents and fabric of the universe and how do they interact?
(D) How can we explore and understand the extremes of the universe?

The work is also relevant to Work Packages 8.7 of the LISA collaboration, an ESA/NASA mission for a space based gravitational wave observatory.

IMPACT: High - potential to discover signatures of dark matter and distinguish between high and low mass candidates. Development of publicly available code also provides an invaluable resource for other researchers.

COLLABORATORS: The student will work with the GRChombo team (www.grchombo.org), as part of a project to develop an open source numerical relativity code. This is a UK-led community resource, developed in collaboration with Intel, as a flagship example of their High Performance Computing (HPC) technologies. They will also join the LISA collaboration as an associate member.