RUNNING COUPLING
COLOR STRINGS
PHASE DIAGRAM
QCD is the theory of the strong force. Quarks carry color charge (red, green, blue) and interact via gluons.
Asymptotic freedom: αs(Q²) → 0 as Q² → ∞ — quarks behave like free particles at short distances (Gross, Politzer, Wilczek 1973).
Confinement: the color-electric flux tube (string tension κ ≈ 1 GeV/fm) grows linearly with quark separation, preventing isolation.
At high T or density, matter transitions to a quark-gluon plasma (QGP) — the state of the early universe microseconds after the Big Bang.