# The Strong Force: From Quarks to Hadrons and Nuclei

## Abstract

The strong force, which binds quarks and gluons together in hadrons, is commonly attributed to the color charge, a property of quarks and gluons only, which is analogous to the electric charge responsible for the electromagnetic force. In analogy to the electromagnetic force which is thought to be mediated by the exchange of virtual photons, the strong force is thought to be mediated by the exchange of gluons. At femtometer distances the strong force is much stronger than the Coulombic repulsion and increases with distance, a behavior called *colorconfinement*. At shorter distances the strong force becomes weaker, a behavior known as *asymptotic freedom*. The residual strong force, which keeps protons and neutrons bound in nuclei, is typically a factor of 100 weaker than the strong force. It is thought to be analogous to the van der Waals forces in chemistry which originate from the Coulombic forces but are much weaker due to charge screening. A similar type of color charge screening is thought to make the residual strong interaction (energies of ∼ 5 *MeV* ) much weaker than the strong force itself (energies of ∼ 500 *MeV* ). A first disappointment for the newcomer is that there is no simple expression, such as Coulomb’s or Newton’s law, allowing for fast computation of the strong force between two particles. The current theory of the strong force is quantum chromodynamics (QCD) and one of its predictions is that for energies below ∼ 200 *MeV*, frequently termed QCD scale, the quark-gluon plasma condenses to form hadrons, i.e. baryons and mesons.

## References

- 1.Nambu Y (1984) Quarks: frontiers in elementary particle physics. World Scientific Publishing, SingaporeGoogle Scholar
- 2.Francisco J. Yndura’in (2006) The theory of quark and gluon interactions, 4th Edn. Springer, HeidelbergGoogle Scholar
- 3.Gross DJ, Wilczek F (1973) Ultraviolet behavior of non-abelian gauge theories. Phys Rev Lett 30:1343–1346CrossRefGoogle Scholar
- 4.Politzer HJ (1973) Reliable perturbative results for strong interactions? Phys Rev Lett 30:1346–1349CrossRefGoogle Scholar
- 5.Cabibbo N, Parisi G (1975) Exponential hadronic spectrum and quark liberation. Phys Lett B 59:67–69CrossRefGoogle Scholar
- 6.Braun-Munzinger P, Stachel J (2007) The quest for the quark-gluon plasma. Nature 448:302–309CrossRefGoogle Scholar
- 7.Aoki A, Fodor Z, Katz SD, Szabo KK (2006) The QCD transition temperature: results with physical masses in the continuum limit. Phys Lett B 643:46–54CrossRefGoogle Scholar
- 8.Fodor Z, Katz S (2004) Critical point of QCD at finite T and μ, lattice results for physical quark masses. J High Energy Phys 4:050CrossRefGoogle Scholar
- 9.Kronfeld AS (2008) The weight of the world is quantum chromodynamics. Science 322:1198–1199CrossRefGoogle Scholar
- 10.Recami E, Zanchin VT (1994) The strong coupling constant: its theoretical derivation from a geometric approach to hadron structure. Found Phys Lett 7:85–93CrossRefGoogle Scholar
- 11.Antoniadis I, Arkani-Hamed N, Dimopoulos S, Dvali G (1998) New dimensions at a millimeter to a fermi and superstrings at a TeV. Phys Lett B 436:257–263CrossRefGoogle Scholar
- 12.Pease R (2001) News feature “Brane New World.” Nature 411:986–988CrossRefGoogle Scholar
- 13.Schwarz JH (2007) String theory: progress and problems. Int Prog Theor Phys Suppl 170:214–226. arXiv:hep-th/0702219Google Scholar