= Feynman integral
{c}
A <Feynman integral> is the momentum-space integral associated with a <Feynman diagram>: each independent <loop momentum> is integrated with measure $d^dk/(2\pi)^d$, and <propagators>, vertex numerators and momentum conservation determine the integrand. Its definition also requires a pole prescription and, when divergent, a <regularization in quantum field theory>. <Feynman parameters> combine propagator denominators and permit shifts of loop momenta. A massless two-propagator example is $\int d^dk/[(2\pi)^d k^2(p-k)^2]$, with its causal prescriptions understood. Subtracting local <counterterms> turns a regulated diagram into a finite contribution to a renormalized amplitude.
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