Quark-Gluon Plasma: Coupling, Perturbation Theory & Lattice-Gauge Theory

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In summary, the proof that non-Abelian gauge theories are unconfined so long as the coupling is weak is wrong.
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RedX
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I just finished reading the Wikipedia article on the quark-gluon plasma and it states that because of the large coupling, lattice-gauge theory is used instead of perturbation theory/Feynman diagrams. However, I thought the coupling decreases with increasing energy (asymptotic freedom), so shouldn't perturbation theory work when energies are high enough to produce quark-gluon plasmas? I thought lattice-gauge theory was only useful for showing that quarks are confined at low energies/large couplings.
 
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You are right that in few body systems, the strong coupling decreasing at high energy, one may use perturbation methods. But note that wikipedia articles mentions that non-perturbative lattice calculations are used to deal with the plasma because the density if so high that we have a many-body problem. In fact, one even describes things in terms of chemical potential !
 
  • #3


Humanino,

I have a question. Consider that the few body system under study is the deuteron [NP], of course we then have 6 quarks with strong coupling. Now, suppose we set up an experiment to allow fusion of matter deuteron [NP] with antimatter deuteron [N^P^], with ^ = anti. Would you predict that such a matter+antimatter reaction would produce enough energy to form a quark-gluon plasma ? If so, how would this reaction then be described in terms of chemical potential ?
 
  • #4


Yes. At the energies required to search for QGP (or CGC) it would also be described in terms of chemical potential for two nucleon collisions. It has to do with a tremendous number of virtual partons. For instance at the LHC, you can pretty much consider that the protons are mere bags of glue.
 
  • #5


The quark-gluon plasma is said to be unconfined. Does this result from many-body considerations?

Without taking into account many-body considerations, I've gone through a proof that says Abelian gauge theories are unconfined, and that non-Abelian gauge theories are also unconfined if the gauge coupling is small, and confined if the gauge coupling is large.

But what's confusing is that the book then sends the lattice spacing to zero, and says that the coupling constant then goes to zero (which I guess is asymptotic freedom), but no phase transition is undergone: the phase is still confined! So does this mean that even when the coupling gets very weak at high energies, quarks are still confined? If so, then that proof that non-Abelian gauge theories are unconfined so long as the coupling is weak is wrong?
 

1. What is quark-gluon plasma?

Quark-gluon plasma is a state of matter that existed right after the Big Bang and is recreated in high-energy collisions of heavy nuclei, such as in particle accelerators. It is a hot, dense soup of quarks and gluons, which are the fundamental building blocks of protons and neutrons.

2. How is quark-gluon plasma studied?

Quark-gluon plasma is studied through a combination of experimental observations and theoretical calculations. Experiments, such as at the Large Hadron Collider, collide heavy nuclei at high energies to create and study the plasma. Theoretical calculations use perturbation theory and lattice-gauge theory to understand the properties and behavior of the plasma.

3. What is perturbation theory?

Perturbation theory is a mathematical technique used to calculate the properties of a system that can be slightly altered from a known, simpler system. In the context of quark-gluon plasma, perturbation theory is used to calculate the interactions between quarks and gluons in the plasma, which allows us to understand its properties and behavior.

4. What is lattice-gauge theory?

Lattice-gauge theory is a computational technique used to study the interactions between quarks and gluons in the plasma. It involves dividing space and time into a grid, or lattice, and using numerical simulations to calculate the properties of the plasma. This approach allows us to study the plasma at high temperatures and densities, which are difficult to recreate in experiments.

5. How does quark-gluon plasma support our understanding of the early universe?

Studying quark-gluon plasma allows us to understand the fundamental laws of physics that governed the early universe, right after the Big Bang. By recreating the conditions of the early universe in high-energy collisions, we can test and refine our theories of how matter and energy interact. This can also provide insights into the origins of the universe and help us understand how it has evolved over time.

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