# To produce a quark from universe

1. Sep 20, 2014

### Quarlep

Lets think we have a paticle system which consisting two quarks and they are combined.Then here I learned somehing strange.If we separate this two quarks the universe creates two quarks from universe so first we have 1 quark pairs now we have two. In this process virtual quarks (the matter ones) combined the quarks.Here comes my question Whats happened the other two virtual quarks (the antimatter ones).

Thanks

2. Sep 20, 2014

### ChrisVer

Not exactly the universe. They pop out from the vacuum as real particles (on-shell particles) because the available energy is enough.
I don't exactly understand the rest of the question, you had 1 pair of quarks, let's say $q \bar{q}$
and you move them away (since latex doesn't help, allow me to write $\bar{q}$ as q*)
q---q*
q--------q*
q----[q* q]---q*
(qq*)+(qq*)

In [..] I put the popped up quarks... So what do you mean by matter or antimatter? In the first place you can't have a particle consisting of two quarks. The least are the mesons consisting of $q \bar{q}$ and then are the baryons consisted of $q q q$ In the case you try to move away a quark from a baryon, you'll most probably get a meson out.:
qqq
qq---q
qq------q
qq---[q q*]--q
(qqq) + (q*q)

This happens because of the properties of QCD... In electomagnetism, taking two charges away from each other, the energy density between them gets dispersed and so weakens...In QCD though the picture is different, and it looks like a string (no wonder string theory was first proposed to explain strong interactions). The energy density between q and q* gets concentrated around their distance (more correctly the potential becomes that of a string), and if it gets enough [qq*] can be created.

3. Sep 20, 2014

### Quarlep

I am sorry about my english I am live in Turkey.
I mean q and q* as that you have wrote it.
I understand that I didn't ask the question right point of view. Let me clear the question lets suppose we have qq than If we separate them then
q......q
q.....(q*q)......q
I want to separate qq but I made a mistake which in universe theres no qq.
This is true isnt it there no qq in universe

Thanks

4. Sep 20, 2014

### ChrisVer

When you want to find allowed quark configurations you have to be able to make color singlets.
The fundamental representation of the $SU(3)$ gauge symmetry (the symmetry of QCD) is the $\textbf{3}$.
Now out of it, in order to make a singlet you have to use: $\textbf{3} \otimes \textbf{3} \otimes \textbf{3}= \textbf{10} \oplus \textbf{8} \oplus \textbf{8} \oplus \textbf{1}$ which contains a singlet $\textbf{1}$ (color neutral).
Having two quarks (3 colors each) can't give a neutral combination: $\textbf{3} \otimes \textbf{3} = \textbf{6} \oplus \textbf{3}$.

In addition to the fundamental representation $\textbf{3}$ of SU(3), you can also have the antifundamental repr, $\bar{\textbf{3}}$ which together gives you the adjoint representation and a singlet.
$\textbf{3} \otimes \bar{\textbf{3}} = \textbf{8} \oplus \textbf{1}$
That's why a quark can be combined with an antiquark to give a color neutral combination.

To make this more illustrative, I will also add that the reason you say that the singlets $\textbf{1}$ are color neutral, is because they transform identically under an $SU_{color}(3)$ transformation (that's why they are neutral)