In quantum field theory, the theta vacuum is the semi-classical vacuum state of non-abelian Yang–Mills theories specified by the vacuum angle θ that arises when the state is written as a superposition of an infinite set of topologically distinct vacuum states. The dynamical effects of the vacuum are captured in the Lagrangian formalism through the presence of a θ-term which in quantum chromodynamics leads to the fine tuning problem known as the strong CP problem. It was discovered in 1976 by Curtis Callan, Roger Dashen, and David Gross,[1] and independently by Roman Jackiw and Claudio Rebbi.[2]
- ^ Callan, C.G.; Dashen, R.F.; Gross, D.J. (1976). "The structure of the gauge theory vacuum". Physics Letters B. 63 (3): 334–340. Bibcode:1976PhLB...63..334C. doi:10.1016/0370-2693(76)90277-X.
- ^ Jackiw, R.; Rebbi, C. (1976). "Vacuum Periodicity in a Yang–Mills Quantum Theory". Physical Review Letters. 37 (3): 172–175. Bibcode:1976PhRvL..37..172J. doi:10.1103/PhysRevLett.37.172.