Pohlmeyer charge
In theoretical physics Pohlmeyer charge, named for Klaus Pohlmeyer, is a conserved charge invariant under the Virasoro algebra or its generalization. It can be obtained by expanding the holonomies (generating functions) P T r exp i T μ ∮ d σ A σ ( μ ) ( σ ) {\displaystyle P\,Tr\,\exp iT_{\mu }\oint d\sigma A_{\sigma }^{(\mu )}(\sigma )} with respect to the constant matrices T. The gauge field A σ μ {\displaystyle A_{\sigma }^{\mu }} is defined as a combination of ∂ X μ {\displaystyle \partial X^{\mu }} and its conjugate.