In particle physics, the X and Y bosons (sometimes collectively called "X bosons") are hypothetical elementary particles analogous to the W and Z bosons, but corresponding to a unified force predicted by the Georgi–Glashow model, a grand unified theory (GUT). However, the Hyper-Kamiokande has put a lower bound on the proton's half-life as around 1034 years. Since some grand unified theories such as the Georgi–Glashow model predict a half-life less than this, then the existence of X and Y bosons, as formulated by this particular model, remain hypothetical.