feynlag.pheno.propagator.vector_propagator

feynlag.pheno.propagator.vector_propagator(q, q2, mass, a, b, width=0)

−i(g_ab − q_a q_b/m²)/(q² − m² + i m Γ); massless (Feynman gauge) reduces to −i g_ab/q².

Parameters:

• q – callable q(index) -> TensExpr, as in vector_propagator_numerator(); unused (and may be None) for a massless mediator.

• q2 – as in propagator_denominator().

• mass – as in propagator_denominator().

• width – as in propagator_denominator().

• a – the two upper TensorIndex objects; returned with them lowered, matching vector_propagator_numerator().

• b – the two upper TensorIndex objects; returned with them lowered, matching vector_propagator_numerator().