I am just beginning to learn about the ideas of the early universe, so this is probably a beginner question.
I understand that protons and neutrons (which are baryons, which are hadrons) are made out of quarks, and quarks are held together by gluons (at a high level). So those are all the ingredients listed in the title "quark-gluon plasma".
But how do electrons and photons come into the picture? Could you describe how this works?
In the wikipedia article Chronology of the Universe, the quark-gluon plasma cools to form hadrons. That makes sense, because hadrons are made out of quarks and gluons.
Then it quickly glosses over a bunch of stuff, basically saying "hadrons and anti-hadrons annihilate to form leptons and anti-leptons, which annihilate... and now the universe is largely dominated by photons interacting frequently with free protons and electrons".
What exactly is happening there? Where did these anti-hadrons come from, and leptons and anti-leptons, and electrons? That's the first time electrons were mentioned.
How did it go from quark-gluon plasma to the formation of atomic nuclei, photons, and electrons? From that point I can imagine the rest and there are lots of resources on how that works, but before that there is very little explanation of the reasoning from what I've seen so far (just wikipedia and arxiv.org mainly).