Spin precession as a new window into disformal scalar fields

TL;DR

This paper explores how spin precession measurements can reveal the presence of disformal scalar fields, providing a new method to probe dark sector interactions with significantly improved constraints over previous approaches.

Contribution

It introduces novel spin-orbit and spin-spin effects caused by disformal scalar fields and demonstrates their potential to constrain such fields using experimental data.

Findings

Spin-dependent effects persist in circular binaries, unlike spin-independent effects.

Constraints from Gravity Probe B improve previous bounds by over 5 orders of magnitude.

Spin effects offer a promising new window into disformally coupled dark sectors.

Abstract

We launch a first investigation into how a light scalar field coupled both conformally and disformally to matter influences the evolution of spinning point-like bodies. Working directly at the level of the equations of motion, we derive novel spin-orbit and spin-spin effects accurate to leading order in a nonrelativistic and weak-field expansion. Crucially, unlike the spin-independent effects induced by the disformal coupling, which have been shown to vanish in circular binaries due to rotational symmetry, the spin-dependent effects we study here persist even in the limit of zero eccentricity, and so provide a new and qualitatively distinct way of probing these kinds of interactions. To illustrate their potential, we confront our predictions with spin-precession measurements from the Gravity Probe B experiment and find that the resulting constraint improves upon existing bounds from perihelion precession by over 5 orders of magnitude. Our results therefore establish spin effects as a promising window into the disformally coupled dark sector.