Complex sentence: This is why Maxwell fields do not contribute to the spin density J, and they do not imply the presence of affine torsion T. Physicists tend to count any tensor index of a field whose symmetry group is an orthogonal group as contributing to spin.
Split into simpler sentences: This is why Maxwell fields do not contribute to the spin density "J", and they do not imply the presence of affine torsion "T". Physicists usually count any tensor index of a field whose symmetry group is an orthogonal group as contributing to spin.