The vacuum state of classical electromagnetism is usually defined by a solution
to the two sets of Maxwell equations (source free) with a constitutive
constraint that D is proportional to E and H is proportional to B. However, an
addition of a constitutive constraint that links D to E and also to B through a
chiral tensor density gamma, and which also links H to B and also to E via the
hermitian or antihermitean conjugate of this same chiral tensor density, leads
to the same set of wave solutions, propagating with the same phase velocity, but
now the impedance of free space is slightly modified. This conformal factor
does not effect any homogeneous equation sets, but could lead to a lack of a
center of symmetry in the Vacuum! and therefor to a lack of center of symmetry
for the universe.
