Periodic Reporting for period 2 - SHADE (Statistical Host Identification As a Test of Dark Energy)
Okres sprawozdawczy: 2022-08-01 do 2023-09-30
The ERC Starting Grant SHADE is building crucial tools that allow the latest gravitational wave data to be brought to bear on these key scientific questions. Specifically, my team is constructing the statistical frameworks and software tools to deploy a new technique called `dark sirens', which maximally extracts information from gravitational wave detections. We are also creating new simulations of how the cosmic web of dark matter forms in the universe, to understand how this process is sensitive to the laws of gravity. The aims of SHADE are to create tools which go beyond the current frontiers in these areas, and then combine these with most recent data from both gravitational wave detectors and galaxy surveys. In this way, we seek to answer some of the biggest questions in cosmology: what are the true laws of gravity? What do these imply for the future expansion rate of the universe?
2) My team has produced a new simulation code to study the collapse of dark matter in the universe, called Hi-COLA. In particular, Hi-COLA can study the formation of the cosmic web within a very broad class of gravity theories beyond Einstein's General Relativity. Version one of Hi-COLA has been publicly released, and we presented the code and its initial results in a paper (published in JCAP).
3) We have developed a new algorithm for completing galaxy catalogues, i.e. modelling the missing galaxies from a survey. This is a key prescription that is used in the dark sirens analysis of 1).
4) We have performed a new set of calculations for relativistic effects in large-scale structure in luminosity distance space. These are a necessary step for future cross-correlations of gravitational wave data with galaxy surveys. This work also enabled us to model for the first time key properties of gravitational wave sources called evolution bias and magnification bias.
5) We studied how a change in the propagation speed of gravitational waves could be detected by both the future LISA space-based detector, and a `multi band' combination of future detectors. We find that a departure from GR can be strongly constrained via one or both of these methods, at lower energy scales than is possible currently. This will push our tests of General Relativity into a new regime, informing future ideas regarding dark energy (the mysterious substance which is thought to drive the expansion rate of the universe). This work is written up in two published papers.
Our simulation code Hi-COLA went beyond the state of the art by being the first code which is able to flexibly handle many different theories of modified gravity. Previously individual simulation suites were written and hard-coded for separate theories of gravity. Our work should hugely improve the efficiency of large-scale structure simulations in this regard, as well as opening up the study of many gravity theories which were not possible before.
Going forward, one key component of the grant work will be the analyse the latest data from the gravitational wave detectors -- this is being collected at present, and is not publicly available. We also hope to extend our analyses to incorporate a broader range of departures from GR. In Hi-COLA we plan to implement a new kind of screening phenomenon which will likewise generalise its scope. We will then be in an excellent position to start combining the results from the two project strands here, i.e. both gravitational and electromagnetic data. In this way we aim to make the most decisive statements about departures from General Relativity, having a significant impact on the community directions in both observational and theoretical cosmology.