Periodic Reporting for period 4 - MassiveCosmo (Massive Gravity and Cosmology)
Berichtszeitraum: 2021-11-01 bis 2022-10-31
The project is centred on the development of massive gravity as a consistent infrared description of gravity to tackle some of the most important questions at the interface between gravity, cosmology and particle physics such as the cosmological constant problem and physics beyond the standard paradigms. The theory of massive gravity has played an important role in cosmology and gravity and the project has establish consistency constraints both from a theoretical and from a phenomenological perspective. The project has main major developments in two leading directions:
First the project has been deriving phenomenological constraints on models of modified gravity and effective field theories for gravity by exploring the gravitational radiation that arises in binary systems and the potential existence of new black hole solutions in effective field theories from gravity. In parallel the model has been exploring the evolution of gravitational waves and their potential signatures within upcoming surveys.
As a complementary approach, the project has derived new classes of theoretical constraints that can determine whether a low-energy effective field theory could ever enjoy a standard high energy completion. These developments have already played an important role and will continue contributing to understanding how one can model the evolution of our Universe, the behaviour of gravity at large distances and could potentially diagnose new physics beyond the standard model of particle physics. These questions are rooted at the core of our modern society and are linked with the origin and future of our Universe and to the quest for understanding of nature at the most fundamental level.
First the project has been deriving phenomenological constraints on models of modified gravity and effective field theories for gravity by exploring the gravitational radiation that arises in binary systems and the potential existence of new black hole solutions in effective field theories from gravity. In parallel the model has been exploring the evolution of gravitational waves and their potential signatures within upcoming surveys.
As a complementary approach, the project has derived new classes of theoretical constraints that can determine whether a low-energy effective field theory could ever enjoy a standard high energy completion. These developments have already played an important role and will continue contributing to understanding how one can model the evolution of our Universe, the behaviour of gravity at large distances and could potentially diagnose new physics beyond the standard model of particle physics. These questions are rooted at the core of our modern society and are linked with the origin and future of our Universe and to the quest for understanding of nature at the most fundamental level.
Throughout the program, the PI has made significant key developments in constraining massive gravity and other effective field theories that describe different periods of our Universe (inflation, pre big bang, dark energy, physics beyond the standard model, etc…) and has been exported to a wide range of physical systems:
* The PI and her collaborators have unleashed an infinite number of new low-energy constraints that severally constrain any low-energy field theory applicable to cosmology and physics beyond the standard model. In addition, these constraints have been generalized to theories with arbitrary field content, both bosonic and fermionic, including massive gravity using a newly uncovered transversity formalism.
Throughout this program, these newly uncovered bounds were further applied to gravitational effective field theories, massive Galileons and massive gravity, which was shown to satisfy a set of improved positivity bounds while remaining weakly coupled.
* In parallel, the program developed a new class of Proca effective field theory which shown to be relevant for cosmology and potentially providing a new model of dark energy consistent with cosmological history which alleviating the Hubble tension and naturalness issues. The implications of the positivity bounds were derived for all Proca theories where island of consistent regions of parameter space were identified.
* The connection between positivity bounds and causality bounds was explored throughout this ERC program. Importantly, the program has allowed to establish how constraints from high energy completion can be manifested directly at the level for the low-energy EFT via the statement of `infrared causality' which can be applied with has the great benefit of being directly applicable when gravity is dynamical and in curved spacetime. Interestingly, the program proved an exact connection between infrared causality and positivity bounds in situations where both bounds are known and under control. These criteria were then applied to generic shift symmetric EFTs and will be directly relevant for models of dark energy and cosmology more generally.
* In addition the ERC program has allowed to establish the first fully four-dimensional non-linear numerical code that accounts for the behavior of the Vainshtein mechanism in time-dependent systems, relevant for models of modified gravity such as massive gravity.
* Finally, the program has allowed to established new classes of multi-band gravitational constraints that can be used to test theories that modify gravity at low-energy (including potentially massive gravity) and other dark energy EFTs.
* The PI and her collaborators have unleashed an infinite number of new low-energy constraints that severally constrain any low-energy field theory applicable to cosmology and physics beyond the standard model. In addition, these constraints have been generalized to theories with arbitrary field content, both bosonic and fermionic, including massive gravity using a newly uncovered transversity formalism.
Throughout this program, these newly uncovered bounds were further applied to gravitational effective field theories, massive Galileons and massive gravity, which was shown to satisfy a set of improved positivity bounds while remaining weakly coupled.
* In parallel, the program developed a new class of Proca effective field theory which shown to be relevant for cosmology and potentially providing a new model of dark energy consistent with cosmological history which alleviating the Hubble tension and naturalness issues. The implications of the positivity bounds were derived for all Proca theories where island of consistent regions of parameter space were identified.
* The connection between positivity bounds and causality bounds was explored throughout this ERC program. Importantly, the program has allowed to establish how constraints from high energy completion can be manifested directly at the level for the low-energy EFT via the statement of `infrared causality' which can be applied with has the great benefit of being directly applicable when gravity is dynamical and in curved spacetime. Interestingly, the program proved an exact connection between infrared causality and positivity bounds in situations where both bounds are known and under control. These criteria were then applied to generic shift symmetric EFTs and will be directly relevant for models of dark energy and cosmology more generally.
* In addition the ERC program has allowed to establish the first fully four-dimensional non-linear numerical code that accounts for the behavior of the Vainshtein mechanism in time-dependent systems, relevant for models of modified gravity such as massive gravity.
* Finally, the program has allowed to established new classes of multi-band gravitational constraints that can be used to test theories that modify gravity at low-energy (including potentially massive gravity) and other dark energy EFTs.
All directions explored throughout this program has allowed to push developments beyond the state of the art. In fact the program has developed new fields of studies, including:
* development of new connections between the UV and the IR, reason why the PI has been invited to take a leading role in the Snowmass Theory Frontier exercise identifying the future strategic research directions and presenting the future of Effective Field Theory at the Seattle 2022 strategic meeting
* development of new EFT of dark energy
* development of new causality bounds
* development of new classes of multi-band gravitational constraints
* development of new numerical techniques to study screening and tests of gravity.
All these techniques have gone well beyond the state of the art and lead to a succession of results that have been explored throughout the project and will continue being explored by the community now that the program has terminated.
* development of new connections between the UV and the IR, reason why the PI has been invited to take a leading role in the Snowmass Theory Frontier exercise identifying the future strategic research directions and presenting the future of Effective Field Theory at the Seattle 2022 strategic meeting
* development of new EFT of dark energy
* development of new causality bounds
* development of new classes of multi-band gravitational constraints
* development of new numerical techniques to study screening and tests of gravity.
All these techniques have gone well beyond the state of the art and lead to a succession of results that have been explored throughout the project and will continue being explored by the community now that the program has terminated.