Exploring a Fifth Force via the Trajectory of Asteroid Bennu

The Standard Model of particle physics offers a succinct framework to describe the four fundamental forces we know today - gravity, electromagnetism, and the strong and weak nuclear forces. Physicists believe there could be additional forces in nature, which could manifest themselves through new physics beyond the Standard Model. This could occur in the context of dark matter and dark energy, which make up most of the universe but remain largely mysterious. Such a "fifth force" would be mediated by new particles, possibly ultralight bosons, which are particles with extremely small masses. These bosons are predicted in several theoretical extensions of the Standard Model, the framework that describes particles and forces in our universe, but have not yet been observed. Testing for these forces is important because it could lead to discoveries that help explain the nature of dark matter, and solve some of the open questions in physics.

Asteroids like Bennu and Apophis offer a unique opportunity to test for fifth forces because their movements are highly predictable based on well-understood gravitational forces. Space agencies track these objects with exceptional precision using ground-based telescopes, radar, and spacecraft missions like OSIRIS-REx, which provided detailed tracking of Bennu's orbit. Ground-based radar measurements further allow for exact calculations of distance and velocity, making it possible to predict an asteroid's path decades into the future. If a fifth force existed, it could cause subtle deviations from these predictions, offering clues to new physics. Beyond scientific discovery, tracking asteroids is crucial for planetary defense. Near-Earth asteroids, such as Bennu and Apophis, are monitored to assess collision risks with Earth, and missions like NASA’s DART are aimed at deflecting potential threats. These precise methods not only help protect the planet but also enable researchers to detect anomalies in asteroid motion that might reveal forces beyond gravity, providing a powerful tool for testing models of physics that extend beyond the Standard Model.

Luca Visinelli, together with his research group, has identified asteroids as promising probes for these kinds of studies, successfully applying this idea to real-world data. By using precise tracking data from the OSIRIS-Rex mission and ground-based observations, which visited and extensively studied Bennu, the group has looked for tiny deviations from the expected motion that might suggest the presence of a fifth force mediated by ultralight bosons. The study focuses on a particular range of ultralight boson masses, where their analysis provides the tightest limits yet. These findings are relevant to theoretical models that predict forces similar to gravity but much weaker, such as those involving baryon-coupled scalar particles and gauge bosons related to baryon violations, building up over a previous result by the team [https://iopscience.iop.org/article/10.1088/1475-7516/2023/04/031]. Essentially, these results show that tracking the motion of asteroids could be a powerful way to explore new physics beyond the Standard Model, particularly in the search for dark matter particles in the ultralight range.