Noether’s theorems and conserved currents in gauge theories in the presence of fixed fields

Oct 11, 2016
17 pages
Published in:
  • Phys.Rev.D 96 (2017) 2, 025018
  • Published: Jul 24, 2017
e-Print:

Citations per year

20182019202020212022201
Abstract: (APS)
We extend the standard construction of conserved currents for matter fields in general relativity to general gauge theories. In the original construction, the conserved current associated with a spacetime symmetry generated by a Killing field hμ is given by -gTμνhν, where Tμν is the energy-momentum tensor of the matter. We show that if in a Lagrangian field theory that has gauge symmetry in the general Noetherian sense some of the elementary fields are fixed and are invariant under a particular infinitesimal gauge transformation, then there is a current Bμ that is analogous to -gTμνhν and is conserved if the nonfixed fields satisfy their Euler-Lagrange equations. The conservation of Bμ can be seen as a consequence of an identity that is a generalization of ∇μTμν=0 and is a consequence of the gauge symmetry of the Lagrangian. This identity holds in any configuration of the fixed fields if the nonfixed fields satisfy their Euler-Lagrange equations. We also show that Bμ differs from the relevant canonical Noether current by the sum of an identically conserved current and a term that vanishes if the nonfixed fields are on shell. For an example, we discuss the case of general, possibly fermionic, matter fields propagating in fixed gravitational and Yang-Mills background. We find that in this case the generalization of ∇μTμν=0 is the Lorentz law ∇μTμν-FaνλJaλ=0, which holds as a consequence of the diffeomorphism, local Lorentz and Yang-Mills gauge symmetry of the matter Lagrangian. For a second simple example, we consider the case of general fields propagating in a background that consists of a gravitational and a real scalar field.
Note:
  • 28 pages, LaTeX, minor changes, journal reference added
  • symmetry: gauge
  • current: conservation law
  • matter: symmetry
  • symmetry: Noether
  • current: Noether
  • background: Yang-Mills
  • transformation: gauge
  • symmetry: space-time
  • diffeomorphism: invariance
  • tensor: energy-momentum