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 unified force predicted by the Georgi–Glashow model, a grand unified theory (GUT).

Since the X and Y boson mediate the grand unified force, they would have unusual high mass, which requires more energy to create than the reach of any current particle collider experiment. Significantly, the X and Y bosons couple quarks (constituents of protons and others) to leptons (such as positrons), allowing violation of the conservation of baryon number thus permitting proton decay.

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.

Details
An X boson would have the following two decay modes:
 * X Boson$4⁄3$ &thinsp; &rarr; &thinsp; Up quark$1⁄3$ &thinsp; + &thinsp; Up quark$1⁄2$
 * X Boson$1⁄2$ &thinsp; &rarr; &thinsp; Positron$2⁄3$ &thinsp; + &thinsp; Down antiquark$5⁄3$

where the two decay products in each process have opposite chirality, Up quark is an up quark, Down antiquark is a down antiquark, and Positron is a positron.

A Y boson would have the following three decay modes:
 * Y Boson$+$ &thinsp; &rarr; &thinsp; Positron$L$ &thinsp; + &thinsp; Up antiquark$R$
 * Y Boson$+$ &thinsp; &rarr; &thinsp; Down quark$L$ &thinsp; + &thinsp; Up quark$R$
 * Y Boson$+$ &thinsp; &rarr; &thinsp; Down antiquark$L$ &thinsp; + &thinsp; $Electron antineutrino$$R$

where Up antiquark is an up antiquark and $Electron antineutrino$ is an electron antineutrino.

The first product of each decay has left-handed chirality and the second has right-handed chirality, which always produces one fermion with the same handedness that would be produced by the decay of a W boson, and one fermion with contrary handedness ("wrong handed").

Similar decay products exist for the other quark-lepton generations.

In these reactions, neither the lepton number ($+$) nor the baryon number ($L$) is separately conserved, but the combination $R$ is. Different branching ratios between the X boson and its antiparticle (as is the case with the K-meson) would explain baryogenesis. For instance, if an X Boson$+$ / X Boson$L$ pair is created out of energy, and they follow the two branches described above:
 * X Boson$R$ &rarr; Up quark$L$ + Up quark$B$ ,
 * X Boson$B &minus; L$ &rarr; Down quark$+$ + Electron$−$ ;

re-grouping the result &thinsp; ( Up quark + Up quark + Down quark ) + Electron $&thinsp;=&thinsp;$ Proton + Electron &thinsp; shows it to be a hydrogen atom.

Origin
The X$+$ and Y$L$ bosons are defined respectively as the six $Q = ± 4⁄3$ and the six $Q = ± 1⁄3$ components of the final two terms of the adjoint 24 representation of SU(5) as it transforms under the standard model's group:


 * $$\mathbf{24}\rightarrow (8,1)_0\oplus (1,3)_0\oplus (1,1)_0\oplus (3,2)_{-\frac{5}{6}}\oplus (\bar{3},2)_{\frac{5}{6}}$$.

The positively-charged X and Y carry anti-color charges (equivalent to having two different normal color charges), while the negatively-charged X and Y carry normal color charges, and the signs of the Y bosons' weak isospins are always opposite the signs of their electric charges. In terms of their action on $$\ \mathbb{C}^5\ ,$$ X bosons rotate between a color index and the weak isospin-up index, while Y bosons rotate between a color index and the weak isospin-down index.