# TAPIR Seminar

Friday, December 11, 2020
2:00pm to 3:00pm
Online Event
Angular momentum in Einstein-Maxwell theory
Alexander Grant, Postdoctoral Research Associate, Department of Physics, University of Virginia,

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https://caltech.zoom.us/j/92271559087?pwd=TFQ2YVk2N0FpSzhlR3JvZlFENTUyQT09

In electromagnetism in flat spacetime, the flux of angular momentum through null infinity, as computed through the stress-energy tensor, depends on both radiative and Coulombic degrees of freedom.  In the first half of this talk, I will show that this unexpected property holds more generally for electromagnetism in non-dynamical, asymptotically flat spacetimes.  Moreover, I will discuss alternative definitions of angular momentum that, in particular, depend only on radiative degrees of freedom.  In the second half of this talk, I will discuss asymptotic charges (such as mass and angular momentum) in Einstein-Maxwell theory, where the metric is now dynamical.  One could define these charges by using the same expressions as in vacuum general relativity; however, this prescription results in fluxes for angular momentum that depend on Coulombic degrees of freedom, as they did in the non-dynamical case.  An alternative definition is to use the prescription of Wald and Zoupas to define these charges, an approach that can be used for any theory with a Lagrangian formulation.  Using this definition, the flux of angular momentum depends only on radiative degrees of freedom.