The energy-momentum tensor of the field is asymmet-
ric. This has important consequences. This asymmetry
is shown to be necessary for the coupling of the total spin
density (magnetization) and the orbital angular momen-
tum of matter. The asymmetry cancels exactly the effect
of the torque density in the dynamical equation of the
field spin density with the general result that the spin of
the field is decoupled from the polarization of matter.
https://arxiv.org/pdf/1703.02109.pdf
The internal torque density represented by the asymme-
try of T μν couples spin and orbital angular momenta. If
the system has no spin, but there is a distributed torque
then T μν − T νμ = −τ μν . Another interesting case is
when the system is isolated; the total angular momen-
tum is conserved, but there may be an exchange between
spin and orbital angular momentum as a result of micro-
scopic interactions.
n this example there is also a spin proportional to the magneti-
zation which will also be transferred to the angular momentum
of the magnet (Einstein-de Haas effect). The coupling is due to
the asymmetry of the stress tensor of the magnet.
The energy-momentum tensor of the field is asymmet-
ric. This has important consequences. This asymmetry
is shown to be necessary for the coupling of the total spin
density (magnetization) and the orbital angular momen-
tum of matter. The asymmetry cancels exactly the effect
of the torque density in the dynamical equation of the
field spin density with the general result that the spin of
the field is decoupled from the polarization of matter.
OH wow - now he's mentioning Basil J. Hiley! I asked in the chat for Jack to comment on Basil J. Hiley. haha. they have corresponded recently - about ten years ago.
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