Can neutron disappearance/reappearance experiments definitively rule out the existence of hidden braneworlds endowed with a copy of the Standard Model?

TL;DR

This paper investigates whether neutron disappearance and reappearance experiments can conclusively rule out hidden braneworlds with Standard Model copies, finding that such experiments cannot universally exclude these hidden worlds except under specific, testable conditions.

Contribution

The study calculates neutron-hidden neutron coupling for various bulk geometries, demonstrating the limitations of experimental tests in definitively ruling out hidden braneworlds.

Findings

Neutron-hidden neutron coupling $g$ varies with bulk geometry.

Experiments cannot universally exclude hidden worlds with Standard Model copies.

Certain scenarios with reachable conditions could test the existence of hidden braneworlds.

Abstract

Many works, aiming to explain the origin of dark matter or dark energy, consider the existence of hidden (brane)worlds parallel to our own visible world - our usual universe - in a multidimensional bulk. Hidden braneworlds allow for hidden copies of the Standard Model. For instance, atoms hidden in a hidden brane could exist as dark matter candidates. As a way to constrain such hypotheses, the possibility for neutron-hidden neutron swapping can be tested thanks to disappearance-reappearance experiments also known as passing-through-walls neutron experiments. The neutron-hidden neutron coupling $g$ can be constrained from those experiments. While $g$ could be arbitrarily small, previous works involving a $M_4 \times R_1$ bulk, with DGP branes, show that $g$ then possesses a value which is reachable experimentally. It is of crucial interest to know if a reachable value for $g$ is universal or not and to estimate its magnitude. Indeed, it would allow, in a near future, to reject definitively - or not - the existence of hidden braneworlds from experiments. In the present paper, we explore this issue by calculating $g$ for DGP branes, for $M_4 \times S_1/Z_2$, $M_4 \times R_2$ and $M_4 \times T^2$ bulks. As a major result, no disappearance-reappearance experiment would definitively universally rules out the existence of hidden worlds endowed with their own copy of Standard Model particles, excepted for specific scenarios with conditions reachable in future experiments.