Vacuum Polarization Tensor
The vacuum polarization is quantified by the vacuum polarization tensor Πμν(p) which describes the dielectric effect as a function of the four-momentum p carried by the photon. Thus the vacuum polarization depends on the momentum transfer, or in other words, the dielectric constant is scale dependent. In particular, for electromagnetism we can write the fine structure constant as an effective momentum-transfer-dependent quantity; to first order in the corrections, we have
where Πμν(p) = (p2 gμν - pμpν) Π(p2) and the subscript 2 denotes the leading order-e2 correction. The tensor structure of Πμν(p) is fixed by the Ward identity.
Read more about this topic: Vacuum Polarization
Famous quotes containing the word vacuum:
“When a daughter tries suicide
and the chimney falls down like a drunk
and the dog chews her tail off
and the kitchen blows up its shiny kettle
and the vacuum cleaner swallows its bag
and the toilet washes itself in tears ...”
—Anne Sexton (1928–1974)