meron (physics)

{{Short description|Half-instanton solution of Yang–Mills theory}}

A meron or half-instanton is a Euclidean space-time solution of the Yang–Mills field equations. It is a singular non-self-dual solution of topological charge 1/2. The instanton is believed to be composed of two merons.{{cite journal |last1=Allan |first1=Curtis |title=A Mechanism for Quark Confinement |journal=Physics Letters |date=1977 |volume=66B |issue=4 |pages=375–381 |doi = 10.1016/0370-2693(77)90019-3|arxiv=hep-ph/9809351 }}

A meron can be viewed as a tunneling event between two Gribov vacua.{{cite journal | last = Actor | first = Alfred | title = Classical solutions of SU(2) Yang-Mills theories | year = 1979 | journal = Reviews of Modern Physics | volume = 51 | issue = 3 | pages = 461–525 | doi = 10.1103/RevModPhys.51.461 |bibcode = 1979RvMP...51..461A }} In that picture, the meron is an event which starts from vacuum, then a Wu–Yang monopole emerges, which then disappears again to leave the vacuum in another Gribov copy.