Vafa–Witten theorem

{{Short description|Theorem concerning spontaneous symmetry breaking}}

{{expert needed|1=Physics|date=August 2017|reason=where is the statement of the theorem?}}

In theoretical physics, the Vafa–Witten theorem, named after Cumrun Vafa and Edward Witten, is a theorem that shows that vector-like global symmetries (those that transform as expected under reflections) such as isospin and baryon number in vector-like gauge theories like quantum chromodynamics cannot be spontaneously broken as long as the theta angle is zero. This theorem can be proved by showing the exponential fall off of the propagator of fermions.

References

| author1-link = Cumrun Vafa | last1 = Vafa | first1 = Cumrun

| author2-link = Edward Witten | last2 = Witten | first2 = Edward

| title = Restrictions on symmetry breaking in vector-like gauge theories

| doi = 10.1016/0550-3213(84)90230-X}}

| doi = 10.1103/PhysRevLett.53.535

| author1-link = Cumrun Vafa | last1 = Vafa | first1 = Cumrun

| author2-link = Edward Witten | last2 = Witten | first2 = Edward

| title = Parity Conservation in Quantum Chromodynamics

| journal = Phys. Rev. Lett.

| volume = 53

| issue = 6

| pages = 535–536

| date = August 1984 | bibcode=1984PhRvL..53..535V}}