Strongly Coupled Chameleons and the Neutronic Quantum Bouncer

TL;DR

This paper explores the potential detection of chameleon fields using ultracold neutrons in gravitational experiments, showing that strong couplings could be detectable or already constrained by existing experiments.

Contribution

It demonstrates that ultracold neutron experiments can set new bounds on chameleon fields, improving previous constraints by three orders of magnitude.

Findings

Detectable energy level shifts for strong couplings ($eta o 10^8$) in upcoming experiments.

Large couplings ($eta o 10^{11}$) would produce observable bound states, now ruled out.

Existing experiments already constrain couplings to $eta o 10^{11}$, surpassing atomic spectrum tests.

Abstract

We consider the potential detection of chameleons using bouncing ultracold neutrons. We show that the presence of a chameleon field over a planar plate would alter the energy levels of ultra cold neutrons in the terrestrial gravitational field. When chameleons are strongly coupled to nuclear matter, $\beta\gtrsim 10^8$, we find that the shift in energy levels would be detectable with the forthcoming GRANIT experiment, where a sensitivity of order one percent of a peV is expected. We also find that an extremely large coupling $\beta\gtrsim 10^{11}$ would lead to new bound states at a distance of order 2 microns, which is already ruled out by previous Grenoble experiments. The resulting bound, $\beta\lesssim 10^{11}$, is already three orders of magnitude better than the upper bound, $\beta\lesssim 10^{14}$, from precision tests of atomic spectra.