Why are leptons antibaryons in gut?

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In summary, when discussing the conservation of baryon number (B) and lepton number (L) in the context of grand unified theories (GUTs), it is important to note that B-L is the conserved quantity while B+L is not. This is a matter of convention and can be seen in the assignment of charges for baryons and leptons. While B-L is an accidental symmetry, B+L is violated at a non-perturbative level in the standard model. Understanding the underlying process and reasoning behind this convention can be clarified by examining the Lagrangian and vertices in an SU(5) model.
  • #1
snorkack
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Why does gut preserve B-L, not B+L?

Also, does weak interaction see both baryons and leptons as particles? Is the helicity required for weak interaction the same (left) for both baryons and leptons and the opposite (right) for both antibaryons and antileptons?
 
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In SU(4) lepton-colour unification it is pretty clear. The U(1) for "B L" must be a diagonal of this matrix group, and it must be traceless, and it must have the same charge for the three colours. So it is 1/3 for quarks, -1 for Lepton, or opposite. Now, if the full group keeps this assignment, then B-L survives. But you could engineer that the SU(4) leptocolour components are really no lepton and quarks, but leptons and antiquarks. Or that the full "B L" mixes with some othe U(1). So it is not a strong requisite.
 
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  • #3
snorkack said:
Why does gut preserve B-L, not B+L?

If (and only if) both B+L and B-L are conserved, B and L are conserved separately.

If you ask why the conserved quantity has a minus sign and not a plus sign, the answer is "convention". By convention, the e- has L=1 and the e+ has L=-1. We could have defined it the other way, and then B+L would be conserved.
 
  • #4
Vanadium 50 said:
If (and only if) both B+L and B-L are conserved, B and L are conserved separately.
Yes. As they are outside GUT.
So, if B separately is not conserved, why should there be conservation of B-L, but not conservation of B+L without conserving B-L, or not conserving either B+L or B-L?
Vanadium 50 said:
If you ask why the conserved quantity has a minus sign and not a plus sign, the answer is "convention". By convention, the e- has L=1 and the e+ has L=-1. We could have defined it the other way, and then B+L would be conserved.
But that´s a matter of sign definition. I am asking substantive reason for the underlying process. Why does GUT allow baryon decay to antileptons while forbidding baryon decay to leptons?
 
  • #5
Doesn't the last concern of yours imply CP violation instead?
It's totally different to sign convention.
 
  • #6
snorkack said:
Yes. As they are outside GUT.
So, if B separately is not conserved, why should there be conservation of B-L, but not conservation of B+L without conserving B-L, or not conserving either B+L or B-L?

B+L is violated on a non-perturbative level in the standard model, while B-L is an accidental symmetry. That it is B-L rather than B+L that is conserved is of course only a sign convention of what leptonic and baryonic charges we assign to the fields.
 
  • #7
I will repeat the point: The U(1) generator must be traceless. So it has more sense a convention which calls it "B-L" than the contrary.
 
  • #8
I think writing the fields' Lagrangian, in an SU(5) model for example, and look at the vertices can help you clarify your problem.
 

Related to Why are leptons antibaryons in gut?

1. What are leptons and antibaryons?

Leptons are a type of elementary particle that make up matter. They include electrons, muons, and taus. Antileptons, also known as antibaryons, are the antimatter counterparts to leptons.

2. Why are leptons considered antibaryons in gut?

In the context of particle physics, the term "antibaryon" is often used to refer to any type of antimatter particle that is composed of three antiquarks. This includes antiprotons and antineutrons, which are considered antibaryons in the atomic nucleus. In the context of the Grand Unified Theory (GUT), leptons are also considered antibaryons because they have similar properties to baryons, such as having a spin of 1/2.

3. How are leptons and antibaryons related in GUT?

In GUT, leptons and antibaryons are considered to be part of the same family of particles known as fermions. They are both made up of three fundamental particles called quarks, and they have similar properties such as charge and spin. However, they differ in terms of their mass and the fact that leptons do not participate in the strong nuclear force like antibaryons do.

4. What is the significance of leptons being antibaryons in GUT?

The fact that leptons are considered antibaryons in GUT is significant because it provides a theoretical framework for understanding the fundamental particles and forces in the universe. It allows for a unification of the strong, weak, and electromagnetic forces, and it helps to explain why there is an imbalance between matter and antimatter in the universe.

5. How does the concept of leptons as antibaryons in GUT impact our understanding of the universe?

The concept of leptons being antibaryons in GUT provides a deeper understanding of the fundamental particles and forces in the universe. It helps to explain why there is more matter than antimatter, and it provides a framework for studying the interactions between particles at the smallest scales. This knowledge can also have practical applications, such as in the development of new technologies and medical treatments.

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