Gravitational Waves from Strings with Adaptive Mesh Refinement

ongoing

Cosmic strings are motivated by simple extensions to the Standard Model of particle physics (BSM), including dark matter axion models (axion cosmology), superstring theory and grand unified theories. If present, cosmic strings will radiate gravitational waves (GWs) which could be detected by current and future GW experiments, such as LIGO-Virgo-KAGRA (LVK), LISA and the Einstein Telescope. Detection or bounds placed on cosmic strings provide deep insight into BSM particle physics models, and are a potential discovery channel for new fundamental fields. Searches for cosmic strings in LVK data have to date used analytic waveforms predicted using the Nambu-Goto (NG) approximation. This is problematic, as the NG model is known to be inaccurate in precisely the high-curvature regions from which the strongest GW signals are emitted. These waveforms have never been verified by numerical simulation, so current matched template searches may not provide useful information or constraints. GWStrings will address this by producing the first waveforms for cosmic string cusp configurations in full numerical relativity (NR) and using them to perform a matched template search in the LVK data. GWStrings will also match these waveforms to current analytic models to determine their validity. Simulations will be implemented using the adaptive mesh refinement (AMR) NR code, GRChombo. GWStrings will require crucial input from researchers in two key areas: theoretical understanding of fundamental fields in the strong gravity regime, and GW source modelling and data analysis. The first will be provided through a secondment at Sapienza University of Rome in the world-leading gravity theory group of Prof Paulo Pani. The second will be provided by the HECAP group at ICTP, the host institute, whose foundational focus lies in connecting astroparticle physics, high energy physics and cosmology, where the project supervisor Prof Giovanni Villadoro, is an internationally-recognised expert in high energy physics theory and phenomenology, particularly BSM axion strings.