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 Sci Advisor P: 1,136 The electromagnetic Chern Simons spin density is only know since the nineteen seventies from advanced Quantum Field Theory on the chiral anomalies. It is the correct form of the electromagnetic spin- density of the vacuum. It can be expressed as a 4-vector as follows: $$\mbox{Chern Simons Spin Density:}\qquad \vec{\cal S}\ =\ \textsf{D} \times \vec{A}\ \ +\ \ \textsf{H}\ \Phi\ ,\qquad {\cal S}^o \ =\ \frac{1}{c}(\textsf{D}\cdot\vec{A})\ \quad$$ Which are just the familiar electromagnetic potentials and fields. It's still virtually unknown to the wider audience, hidden as it is in the more advanced QFT texts in a less accessible form. Especially interesting are the electromagnetic spin density fields of the electron and the photon. For instance: Linear polarized photons, originating from spin 1 transitions, don't carry net spin, however, they still contain the information of the original spin sign within the canceling, non zero, components of the EM spin density from electric and magnetic vacuum polarization. Linear photons therefor come in two types which might be physically distinguishable in entanglement experiments. $$\begin{array}{|l|c|c|c|c|} \hline &&&& \\ \mbox{polarization} &\ \ \mbox{orbit spin}\ \ &\ \mbox{EM spin}\ \vec{S}\ &\ \textsf{ D} \times \vec{A}\ & \ \ \ \textsf{ H}\ \Phi\ \ \\ &&&& \\ \hline &&&& \\ \mbox{Linear} & +\hbar & 0 & +\hbar & -\hbar \\ \mbox{Linear} & -\hbar & 0 & -\hbar & +\hbar \\ \mbox{Circular} & +\hbar & +\hbar & +\hbar & \ \ 0 \\ \mbox{Circular} & -\hbar & -\hbar & -\hbar & \ \ 0 \\ &&&& \\ \hline \end{array}$$ The current experimental status suggests that we have to either, give up locality and/or reality, or show that Malus law can be violated in polarizing beam splitters. The two types of linear polarized photons might open the door to the latter possibility. The derivations (which I had to do myself since somehow one can't find these anywhere) and many details can be found in my paper, here: The electro magnetic Chern Simons spin density Regards, Hans