I New scientist SU(5) Unification without Proton Decay

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new scientist latest issue covers this paper

SU(5) Unification without Proton Decay
Bartosz Fornal, Benjamin Grinstein
(Submitted on 26 Jun 2017 (v1), last revised 13 Nov 2017 (this version, v2))
We construct a four-dimensional SU(5) grand unified theory in which the proton is stable. The Standard Model leptons reside in the 5 and 10 irreps of SU(5), whereas the quarks live in the 40 and 50 irreps. The SU(5) gauge symmetry is broken by the vacuum expectation values of the scalar 24 and 75 irreps. All non-Standard Model fields are heavy. Stability of the proton requires three relations between the parameters of the model to hold. However, abandoning the requirement of absolute proton stability, the model fulfills current experimental constraints without fine-tuning.
Comments: 5 pages; v2: accepted by Physical Review Letters
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Cite as: arXiv:1706.08535 [hep-ph]
(or arXiv:1706.08535v2 [hep-ph] for this version)

with some reviews and quotes by particle HEP physicists that its promising. a modification of SU(5) GUT, without SUSY, that makes protons stable.
 

ohwilleke

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Good catch.
 
725
82
Good catch.
what do you think is the significance of this paper's theory? SU(5) GUT without proton decay or SUSY?
 
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That it's possible to construct a GUT with a simple gauge group that does not have proton decay. Lower limits on the proton's mean life are getting high enough to be able to test various GUT's.

I decided to put my Semisimple Lie Algebras software to work to see what is plausible. I'll give the highest-weight values of the irreps and also their Standard-Model breakdowns as (QCD,WIS,WHC).
Leptons:
5 - (1,0,0,0) - (3*,1,1/3) + (1,2,-1/2)
10 - (0,1,0,0) - (3,1,2/3) + (3*,2,-1/6) + (1,1,-1)
10* - (0,0,1,0) - (3*,1,-2/3) + (3,2,1/6) + (1,1,1)
5* - (0,0,0,1) - (3/1,-1/3) + (1,2,1/2)
Right-handed neutrinos are Standard-Model and SU(5) singlets.
Quarks:
40 - (1,1,0,0) - (8,1,1) + (6*,2,1/6) + (3,2,1/6) + (3*,3,-2/3) + (3*,1,-2/3) + (1,2,-3/2)
40* - (0,0,1,1) - (8,1,-1) + (6,2,-1/6) + (3*,2,-1/6) + (3,3,2/3) + (3,1,2/3) + (1,2,3/2)
50 - (0,2,0,0) - (6*,3,-1/3) + (6,1,4/3) + (8,2,1/2) + (3*,2,-7/6) + (3,1,-1/3) + (1,1,-2)
50* - (0,0,2,0) - (6,3,1/3) + (6*,1,-4/3) + (8,2,-1/2) + (3,2,7/6) + (3*,1,1/3) + (1,1,2)
Scalars:
24 - (1,0,0,1) - (8,1,0) + (1,3,0) + (1,1,0) + (3*,2,5/6) + (3,2,-5/6)
75 - (0,1,1,0) - (8,3,0) + (8,1,0) + (1,1,0) + (6*,2,-5/6) + (6,2,5/6) + (3*,2,5/6) + (3,2,-5/6) + (3*,1,-5/3) + (3,1,5/3)

Thus, 5: left-handed lepton, 10: right-handed electron, 40: left-handed quark, right-handed up, 50: right-handed down, along with oodles of other particles that get GUT-scale masses from symmetry breaking.

Checking on a (fermion).(fermion).(scalar) sort of coupling, I find that all of them couple with the 24, and that all but the 5 couple with the 75.
 

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