Quantum Chromodynamics and Particle Interactions

Quantum chromodynamics is the theory describing how quarks and gluons bind together through the strong force to form the protons, neutrons, and other hadrons that make up the bulk of visible matter. Because the strong coupling constant grows large at low energies, standard perturbative methods break down, and researchers rely on tools like lattice QCD—a discrete spacetime formulation solved numerically—and renormalization group techniques to extract predictions from first principles. A central challenge is understanding the full spectrum of bound states: alongside familiar mesons and baryons, experiments have uncovered exotic hadrons such as tetraquarks and pentaquarks whose internal structure remains contested, and the precise shape of parton distribution functions—describing how momentum is shared among a hadron's constituents—continues to be refined with each new generation of collider data. Connecting the infrared behavior of QCD Green's functions to observable phenomena like chiral symmetry breaking and confinement remains one of the deepest open problems in the field.

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Keywords

QCDcharmoniummesonsbaryonsparton distributionsrenormalization group