Gravitational Physics from the Universe Large Scales Evolution

Introduction

How does gravity work on cosmological scales? Starting from July 2023, for the very first time in the history of space science, the geometry of the Universe on large scales will be mapped by the Euclid mission, providing the scientific community with a wealth of cosmological data of unprecedented quantity and quality. It will be a transformational moment that will open new ground for testing gravity; yet, unless combined with a theoretical framework able to translate wonderful numbers into concepts, this is bound to be a missed opportunity.

Research Program

This research program - whose proponent is currently serving in the role of co-Lead of the Euclid Theory Working Group - aims at constructing such a framework.

Gravity Comparisons

Euclid will compare the action of gravity on light with that on non-relativistic particles, in a regime vastly different from where General Relativity has been confirmed. Any significant detection of a deviation will have profound consequences.

Signal Analysis

But how to confidently dissect and decipher these potential signals? In the past years, I have laid the groundwork for cosmological tests of gravity, culminating recently in a first reconstruction of gravity from available data. These results are at their infancy, and a leap beyond the current state of the art is urgently required to breach into the smaller, nonlinear scales where statistical errors will be at their lowest. The timing could not be better, with data releases of Euclid expected during the tenure of this proposal.

Predictions and Framework

From an exhaustive exploration of the gravitational landscape under criteria of theoretical viability, we will create predictions of the large-scale phenomenology by broad classes of theories, with an accuracy that meets Euclid requirements.

Comprehensive Framework

These predictions will be used to construct a comprehensive phenomenological framework extending into the nonlinear regime and inform Bayesian non-parametric reconstructions of gravity from the latest data.

Conclusion

As a result, we will provide a completely new view into gravity on large scales.