Angular momentum at null infinity in EinsteinMaxwell theory
Abstract
On Minkowski spacetime, the angular momentum flux through null infinity of Maxwell fields, computed using the stressenergy tensor, depends not only on the radiative degrees of freedom, but also on the Coulombic parts. However, the angular momentum also can be computed using other conserved currents associated with a Killing field, such as the Noether current and the canonical current. The flux computed using these latter two currents are purely radiative. A priori, it is not clear which of these is to be considered the "true" flux of angular momentum for Maxwell fields. This situation carries over to Maxwell fields on nondynamical, asymptotically flat spacetimes for fluxes associated with the Lorentz symmetries in the asymptotic BMS algebra. We investigate this question of angular momentum flux in full EinsteinMaxwell theory. Using the prescription of Wald and Zoupas, we compute the charges associated with any BMS symmetry on crosssections of null infinity. The change of these charges along null infinity then provides a flux. For Lorentz symmetries, the Maxwell fields contribute an additional term in the charge on a crosssection. With this additional term, the flux associated with Lorentz symmetries, e.g. the angular momentum flux, is purely determined by the radiative degrees of freedom of the gravitational and Maxwell fields. In fact, the contribution to this flux by the Maxwell fields is given by the radiative Noether current and not by the stressenergy flux.
 Publication:

arXiv eprints
 Pub Date:
 November 2019
 arXiv:
 arXiv:1911.04514
 Bibcode:
 2019arXiv191104514B
 Keywords:

 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory;
 Mathematical Physics
 EPrint:
 43 pages