NumberOfPolarizations
is an option for DoPolarizationSums
. It specifies the number of polarizations to sum over in the expression. This is relevant only for expressions that contain terms free of polarization vectors. This may occur e.g. if the scalar products involving polarization vectors have already been assigned some particular values. In this case the corresponding terms will be multiplied by the corresponding number of polarizations.
The default value is Automatic
which means that the function will attempt to recognize the correct value automatically by extracting the dimension dim
of the polarization vectors and putting (dim-2)
for massless and (dim-1)
for massive vector bosons. Notice that if the input expression is free of polarization vectors, the setting Automatic
will fail, and the user must specify the correct dimension by hand.
[p, mu] ComplexConjugate[PolarizationVector[p, mu]] PolarizationVector
Here the setting Automatic is sufficient.
[];
FCClearScalarProducts
[p, p] = 0;
ScalarProduct
[p, mu] ComplexConjugate[PolarizationVector[p, mu]] + xyz
PolarizationVector
[%, p, n] DoPolarizationSums
Here it is not
[xyz, p, n] DoPolarizationSums
Setting the number of polarizations by hand fixes the issue
[xyz, p, n, NumberOfPolarizations -> 2]
DoPolarizationSums