New scientist SU(5) Unification without Proton Decay

In summary, this paper proposes a new theory of the proton that does not require proton decay. It is possible to build a GUT theory that is simple and does not require fine-tuning.
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kodama
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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.
 
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Good catch.
 
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ohwilleke said:
Good catch.

what do you think is the significance of this paper's theory? SU(5) GUT without proton decay or SUSY?
 
  • #4
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.
 

1. What is the SU(5) Unification Theory?

The SU(5) Unification Theory is a proposed theory in particle physics that attempts to unify the strong, weak, and electromagnetic interactions into a single mathematical framework. It is based on the special unitary group SU(5), which describes the symmetries of elementary particles.

2. How does the SU(5) Unification Theory explain the absence of proton decay?

The SU(5) Unification Theory predicts that the proton should decay, which is not observed in experiments. To explain this, the theory introduces a new symmetry called baryon number, which prevents the proton from decaying. This symmetry is broken at high energies, which allows for the unification of the strong, weak, and electromagnetic forces, but it remains intact at low energies, thus preventing proton decay.

3. What evidence supports the SU(5) Unification Theory?

One of the main pieces of evidence for the SU(5) Unification Theory is the successful prediction of the weak mixing angle, a fundamental parameter of the weak force. Additionally, the theory has been able to explain the relationship between different particles and forces, such as the similarities between quarks and leptons.

4. What are the implications of the SU(5) Unification Theory?

If the SU(5) Unification Theory is proven to be true, it would have significant implications for our understanding of the fundamental forces and particles in the universe. It would also provide a more elegant and unified explanation for these forces, potentially leading to new discoveries and advancements in physics.

5. Are there any challenges or criticisms of the SU(5) Unification Theory?

One of the main challenges to the SU(5) Unification Theory is the lack of experimental evidence for proton decay. While the theory predicts this decay, it has not been observed in experiments. Additionally, the theory does not include gravity, which is a key force in the universe. Some critics also argue that the theory is too simplistic and does not fully explain the complexity of the universe.

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