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Articles like https://physicsworld.com/a/has-a-new-particle-called-a-leptoquark-been-spotted-at-cern/

report on a difference in the $B$ meson decay chain in electrons to muons which amounts to now $3.1 \sigma$ significance. If this result is further confirmed, i.e. reaching a $5\sigma$ significance it could be explained according to the cited article by the existence of lepto-quarks. If this assumption is correct would it mean that we would already touch upon the Grand unification at around $10^4$GeV whereas the postulated Grand unification is supposed to happen at $10^{14}-10^{15}$GeV? Or do we need a completely new theory in order to explain the possible existence of lepto-quarks at LHC- or slightly higher than LHC-energies?

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I think two concepts are confused here.

Grand Unification symmetry breaking times can be seen here. It means that at the time before GU symmetry breaking all particles are massless, after GU symmetry breaking the extra to SM GU particles acquire a mass, including the possibly seen leptoquark but the electroweak symmetry still holds. After electroweak breaks, all particles have the masses and attributes we have observed in the lab experiments, and used the data to build the theories.

So at our cosmological time, all symmetries are broken and all particles that should have a mass have a mass, including the leptoquarks, if they exist.

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  • $\begingroup$ Thank you for the answer. But actually I don't understand it well. When I refer to the energy scale at $10^{14}-10^{15}$GeV I mean the $X$-boson which is supposed to make possible the proton decay, whereas the violation of the Lepton universality in the $B$ seems to come from a supposed leptoquark of $10^4-10^5$GeV. This would require a new theory (as w/o Susy between the electroweak and the GU scale there is supposed to be nothing new). Or would be GU at lower energy than predicted ? $\endgroup$
    – Frederic Thomas
    Commented Apr 2, 2021 at 13:15
  • $\begingroup$ The X boson at the $10^{14}$ + is before symmetry breaking, and as all particles in the GUT symmetry has zero mass. It acquires mass after GUT symmetry breaking. The leptoquark also. It is analogous with electroweak symmetry breaking, all the particles of the SM before electroweak breaking have zero mass, the group symmetries though are all there. $\endgroup$
    – anna v
    Commented Apr 2, 2021 at 13:46
  • $\begingroup$ Okay, most particles beyond GU energies are massless. But my question is more basic. Where does the possible Leptoquark come from (without or with non-zero mass) ? $\endgroup$
    – Frederic Thomas
    Commented Apr 2, 2021 at 14:31
  • $\begingroup$ From the representations of the symmetry groups of the specific GUT model. .Look at the en.wikipedia.org/wiki/Eightfold_way_(physics) . Similar to the representation of hadrons, the meson octet for example, there are group representations making up leptoquarks for GUT symmetries. $\endgroup$
    – anna v
    Commented Apr 2, 2021 at 15:24
  • $\begingroup$ As an expermantalist, I am not sure that a zero mass leptoquark exists before GUT symmetry breaking, because even zero mass particles combined acquire a mass from the added four vectors. The representations in quantum numbers though should exist allowing for the possibility of a leptoquark after breaking. $\endgroup$
    – anna v
    Commented Apr 2, 2021 at 16:04

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