feynlag.pheno.propagator.vector_propagator_numerator

feynlag.pheno.propagator.vector_propagator_numerator(q, m, a, b)

The massive-vector numerator g_{ab} − q_a q_b/m² (both indices lower).

Parameters:

• q – a callable q(index) giving the propagator four-momentum as a tensor expression (e.g. lambda i: p2(i) + p3(i) — the sum of the two fermion momenta).

• m – the vector mass.

• a – the two (upper) Lorentz TensorIndex objects; the numerator is returned with them lowered (-a, -b) so it contracts with upper indices on the adjacent vertices.

• b – the two (upper) Lorentz TensorIndex objects; the numerator is returned with them lowered (-a, -b) so it contracts with upper indices on the adjacent vertices.