What Is a Lepto-Diquark in Particle Physics?

[Murtuza Tipu]

[mod edit] This question was originally asked at https://physics.stackexchange.com/questions/115053/whats-a-lepto-diquark

This questions refers to Slansky's Group theory for unified model building, page 106 of chapter 7.

He assigns the weight (1)(01), which is stepwise projected from E6 to SU(2)×SU(3), to a state which he calls a 4/3-charged antilepto-diquark.

I assume that the diquark comes from the 2×2/3 for the charge and the lepton from the fact that it will probably be contained in a multiplet together with the leptons...

What I don't understand:

Where does the charge assignement 4/3 comes from?

On the basis of the weight I would have called it a anti-up quark, since it is the upper component of the doublet, the 1 in the first brackets, and transforms as a 3¯ under SU(3) (since (01) is the corresponding fundamental weight). Hence I would assign it a charge 1/3, which later on will be used to determined the charges of the other particles. How does he comes to the conclusion that it must be a diquark?

He comments that it mediates the proton decay. I thought that usually a force is mediated by a boson... Does he means that since the quarks will be together with the leptons in a multiplet, the baryon number does not need to be conserved. Which unable the proton to decay?

Is this diquark something realistic or is it an out-dated object, i.e. ruled out by experiments? When and why was it postulated?

 

[dauto]

All of that happens at scales that are unreachable by experiments so it is not directly ruled out by experiments though it might be ruled out indirectly. he is assigning a lepton number of minus 1 and a Baryon number of plus 2/3 to that state, hence the antilepton-diquark terminology. The electric charge, lepton number, and baryon number are all U(1) gauge charges in this kind of model and can be calculated from the pattern of symmetry braking. Note that you posted that question in the wrong forum. You should've posted that in High Energy Forum, not the Classical Physics forum.