Unraveling the Strong Force: Color vs Favor

In summary, the strong force is a combination of both color and flavor forces. Gluons, which carry a non-vanishing color charge, interact with each other due to the non-abelian nature of SU(3). This is unlike photons, which do not interact with each other because they are color singlets. The distinction between "residual strong force" and "gluon exchange vertex" is important in understanding the total force between hadrons. Additionally, the strong force is also responsible for breaking the parity law.
  • #1
edpell
282
4
Hi this is a very elementary question. Is the strong force a color force? Or a favor force? Or a combination color and favor?

Also with photons (massless) we have a r^-2 force but with massless gluons the force increase with r (do not know as what function) how can this be?

Thanks.
 
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  • #2
The strong force depends on both color and flavor.
The increase in V with r for gluon exchanges is because the gluons interac wilt each other, while photons no not.
 
  • #3
Meir Achuz said:
The strong force depends on both color and flavor.
The increase in V with r for gluon exchanges is because the gluons interac wilt each other, while photons no not.

Thank you this is clear and concise.

May I ask another question? Why do gluons interact with each other while photons do not?
 
  • #4
Meir Achuz said:
The strong force depends on both color and flavor.
I do not agree with that. The strong force does not know about flavor, gluons only know about color charge. The above statement could be made more precise, if one talks about the effective van der Walls force between hadrons for instance. That may be confusing however.

The reason gluons interact with each other is essentially because SU(3) is non-abelian. Directly in the lagragian, one has self interactions between gluons. Another way to say it, gluons belong the adjoint representation, as such are not color singlet, and therefore carry a non-vanishing color charge, to which other gluons answer.
 
  • #5
humanino said:
I do not agree with that. The strong force does not know about flavor, gluons only know about color charge. The above statement could be made more precise, if one talks about the effective van der Walls force between hadrons for instance. That may be confusing however.
\
"Strong force" means, for me, the strong force between quarks and between hadrons.
This force depends on more than just the flavor independent gluon exchange.
Your complaint would be appropriate for the "gluon exchange vertex", not the strong force.
 
  • #6
Meir Achuz said:
"Strong force" means, for me, the strong force between quarks and between hadrons. This force depends on more than just the flavor independent gluon exchange. Your complaint would be appropriate for the "gluon exchange vertex", not the strong force.
It's all a matter of interpretation of the level of the original question. In any case, at the very least your answer should have included "residual strong force", to make it clear that the "gluon vertex" does not depend on flavor. If you look into the literature dating back to when QCD had not been discovered yet, for instance Coleman's first Erice lecture on symmetry, people already knew that the total force between hadrons included "very strong" and "medium strong" forces. This distinction is the origin of the name "strong force".

Otherwise, I can take the opposite illustration : when somebody calls "electroweak interaction between nucleons", it never implicitly includes "gluon exchange as well".
 
  • #7
There's a Science Daily article on the strong force breaking parity law:
http://www.sciencedaily.com/releases...0329214740.htm
 

1. What is the strong force?

The strong force is one of the four fundamental forces of nature, along with gravity, electromagnetism, and weak nuclear force. It is responsible for holding together the nucleus of an atom, which is made up of protons and neutrons. It is the strongest of the four fundamental forces, but it only acts over a very short distance within the nucleus.

2. What is color charge?

Color charge is a property of quarks, which are subatomic particles that make up protons and neutrons. Quarks can have one of three color charges: red, green, or blue. This is not related to the colors we see in everyday life, but rather a way to describe the strong force interactions between quarks. Quarks can also have an "anti-color" charge, such as anti-red or anti-blue.

3. How does the strong force differ from electromagnetism and gravity?

The strong force is much stronger than electromagnetism and gravity, but it only acts over a very short distance. This is why we don't see the effects of the strong force in our everyday lives. In contrast, electromagnetism and gravity act over long distances. Also, the strong force only affects particles that have color charge, while electromagnetism and gravity can act on any particles with mass.

4. What is the difference between color and flavor in the strong force?

Color and flavor are two different properties of quarks that are both related to the strong force. Color refers to the three different charges (red, green, and blue) that quarks can have, while flavor refers to the different types of quarks (up, down, charm, strange, top, and bottom). The flavor of a quark is determined by its mass, and the strong force can act differently on different flavors of quarks.

5. How does the strong force hold the nucleus together?

The strong force holds the nucleus together by acting between the quarks that make up protons and neutrons. This force is mediated by particles called gluons, which carry the color charge. Gluons act as "sticky" particles between quarks, holding them together. The strong force also acts to overcome the repulsive force between positively charged protons, allowing the nucleus to stay together.

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