X and Y bosons
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 new type of force predicted by the Georgi–Glashow model , a grand unified theory . 
<triplet> W and Z bosons <subj> elementary particle <obj> has parts of the class <triplet> Georgi–Glashow model <subj> particle physics <obj> instance of