# Constraining Non-local Gravity by S2 star orbits

## TL;DR

This paper investigates non-local gravity theories, especially exponential models, and uses S2 star orbits to constrain these theories, finding limited effects at galactic scales but promising cosmological implications.

## Contribution

It demonstrates that exponential forms of non-local gravity are uniquely consistent with symmetries and provides observational constraints using S2 star data.

## Key findings

- Non-local effects are negligible on S2 star orbits.
- Exponential non-local gravity models fit astronomical data better than Keplerian models.
- Non-local gravity offers richer cosmological phenomenology than ΛCDM.

## Abstract

Non-local theories of gravity have recently gained a lot of interest because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether Symmetries, it can be shown that the only non-trivial form of the distortion function is the exponential one, which is working not only for cosmological mini-superspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak field approximation of this type of non-local gravity, and comparing with the orbits of S2 stars around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Non-local effects do not play a significant role on the orbits of S2 stars around Sgr A*, but give richer phenomenology at cosmological scales than the $\Lambda$CDM model. Also, we show that non-local gravity model gives better agreement between theory and astronomical observations than Keplerian orbits.