I have a pretty large matrix element with stuff like:
SP[p1, e3]*SP[p2, e4]*SP[e1, e2] *...
M^2 has polarization sums, for which I want to apply the rule. First I uncontract my M^2:
Uncontract[Expand[M^2], e3, e1, e2, e4, p1, p2, p3, p4, Pair -> All,
Unique -> False]
Now I have a lot of dummy indices. I want to define the polarization rule, like:
FourVector[e1, mu] FourVector[e1, nu] ->
PolarizationSum[mu, nu, p1]]
But I have to specify indices (mu and nu in this case). Unfortunately, I don't know the names, because the dummy indices get automatically assigned. This auto-assigning is very useful, because I have a lot of dot products, so giving them an index manually is too much work.
Can I define a generic index, like e1(mu?)*e1(nu?), as is possible in Form?
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