Explicit symmetry breaking

In theoretical physics, explicit symmetry breaking is the breaking of a symmetry of a theory by terms in its defining equations of motion (most typically, to the Lagrangian or the Hamiltonian) that do not respect the symmetry. Usually this term is used in situations where these symmetry-breaking terms are small, so that the symmetry is approximately respected by the theory. An example is the spectral line splitting in the Zeeman effect, due to a magnetic interaction perturbation in the Hamiltonian of the atoms involved.

Explicit symmetry breaking differs from spontaneous symmetry breaking. In the latter, the defining equations respect the symmetry but the ground state (vacuum) of the theory breaks it.^[1] In April, 2015, Cambridge University researchers discovered that electromagnetic waves are generated not only due to acceleration of electrons as proposed by James Clerk Maxwell, the great Cambridge based 19th century Physicist, but also as a result of explicit symmetry breaking of the electric field in space associated with electron acceleration. The authors made the observation that two wire transmission lines do not result in radio wave emission despite electron acceleration as the electric field lines have symmetry i.e. invariance along the spatial direction between the transmission lines. But when the wires are flared or opened up, there is a change in the shape of electric field lines, i.e. symmetry is explicitly broken resulting in radiation with an associated non-conserved current which is emitted out from the system. The authors used the observation to argue that acceleration of electron is a necessary but not a sufficient condition for electromagnetic radiation, there must be explicit breaking down of the electric field. ^[2][3][4]

See also

• Symmetry breaking

References