Spinning particles coupled to gravity

TL;DR

This paper discusses how recent experiments with spinning atoms support certain theoretical models of spinning particles in gravity, while challenging others, and proposes new experiments to test the universality of free fall.

Contribution

It clarifies the compatibility of experimental results with a classical Lagrangian model of spinning particles in gravity and proposes new tests for the universality of free fall.

Findings

Experimental results support some classical spinning particle models

Certain models are ruled out by recent experiments

Proposed experiments aim to test universality of free fall

Abstract

Recent experimental work has determined that free falling $^{87}$Rb atoms on Earth, with vertically aligned spins, follow geodesics, thus apparently ruling out spin--gravitation interactions. It is showed that while some spinning matter models coupled to gravitation referenced to in that work seem to be ruled out by the experiment, those same experimental results confirm theoretical results derived from a Lagrangian description of spinning particles coupled to gravity constructed over forty years ago. A proposal to carry out (similar but) different experiments which will help to test the validity of the Universality of Free Fall as opposed to the correctness of the aforementioned Lagrangian theory, is presented.