Modified Gravity: from Compact Objects to Dark Energy

ended

The origin of the accelerated expansion of the Universe remains elusive. The so-called Dark Energy might be a manifestation of modified gravity at very large scales. While near-future observatories will improve the current bounds on such a possibility, they will not likely be conclusive as to its nature. An opportunity arises from the study of modifications of gravity at shorter scales, specifically around compact objects like black holes and neutron stars, recently made possible through gravitational-wave observations. This project aims to dramatically improve the constraints on cosmological modifications of gravity by means of an interdisciplinary approach involving tools from High Energy Physics, and both astrophysical gravitational-wave and cosmological observations. Modified gravity dynamics at different scales can be described in a model-independent way as Effective Field Theories according to symmetry principles. Strong constraints will come from a combined theoretical and phenomenological study within this framework. Both analytical and numerical tools will be developed and employed to qualitatively and quantitatively compute the expected signatures on gravitational-wave astrophysics, allowing to hold these models against observations. The constraints will then be translated to the cosmological modifications of gravity, drawing novel conclusions as to which theories can consistently explain Dark Energy while satisfying bounds across a large range of scales. Ultimately, this project will foster the collaboration among the High Energy Physics, Cosmology and Gravitational-Wave Astrophysics communities, enabling a much faster and efficient progress in the field of modified gravity in general. This includes a more focused use of the available computational resources for time-consuming resource-intensive tasks. The multifaceted training and support received during the action and the competences acquired are aimed at the career development of the fellow.