The neutron. Its properties and basic interactions

This article deals with the interplay between the properties of the neutron and its basic interactions. Many of the neutron’s properties underlie a simple quark model, and we compare related attributes, such as magnetic moment, radius, semileptonic matrix elements, etc., with experimental findings. Particular attention is paid to neutron ββ decay, which provides insights into the Standard Model and beyond. From experiment, the Standard Model description is over-determined, and many precision checks for physics beyond the Standard Model are possible. As these checks address important unanswered questions of particle physics and cosmology, they need to be done as precisely as possible. Free neutron decay is thus a very active field, and many new projects are underway worldwide. Gravity experiments with neutrons are linked to string theories with large volume compactifications and/or low string scale. These theories predict modifications of Newtonian gravity in the sub-millimeter range. Effects could therefore be expected at atomic, nuclear, and even at sub-millimeter scales.