Physics:X and Y bosons

Short description: Hypothetical elementary particles

X^± and Y^± bosons

Composition	Elementary particle
Statistics	Bosonic
Status	Hypothetical
Types	12
Mass	≈ 1015 GeV/c2
Decays into	X: two quarks, or one antiquark and one charged antilepton Y: two quarks, or one antiquark and one charged antilepton, or one antiquark and one antineutrino
electric charge	X: ±4/3 e Y: ±1/3 e
|u}}r charge	triplet or antitriplet
Spin	1
Spin states	3
Weak isospin projection	X: ±1/2 Y: ∓1/2
Weak hypercharge	±5/6
B − L	±2/3
X	0

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⁺   →   u_L   +   u_R

X⁺   →   e⁺_L   +   d_R

where the two decay products in each process have opposite chirality, u is an up quark, d is a down antiquark, and e⁺ is a positron.

A Y boson would have the following three decay modes:

Y⁺   →   e⁺_L   +   u_R

Y⁺   →   d_L   +   u_R

Y⁺   →   d_L   +   ν_eR

where u is an up antiquark and ν_e 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 (L) nor the baryon number (B) is separately conserved, but the combination B − L 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⁺ / X⁻ pair is created out of energy, and they follow the two branches described above:

X⁺ → u_L + u_R ,

X⁻ → d_L + e⁻_R ;

re-grouping the result   ( u + u + d ) + e⁻  =  Proton + e⁻   shows it to be a hydrogen atom.

Origin

The X^± and Y^± 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:

[math]\displaystyle{ \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}} }[/math].

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 [math]\displaystyle{ \ \mathbb{C}^5\ , }[/math] 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.

See also

• B − L
• Grand unification theory
• Leptoquark
• Proton decay
• W' and Z' bosons