FCLoopGetFeynAmpDenominators[expr, {k1,k2,...}, head]
extracts all single propagator denominators present in the expression
that depend on the loop momenta k1, k2, ....
The function returns a list of two elements. The first one contains
the original expression with selected denominators wrapped with
head. The second one is the list of relevant
denominators
Setting the option "Massless" to Truewill
select only massless denominators.
The option Momentum specifies the dependency on external
momenta. When set to a list of momenta, relevant propagators will be
selected irrespective of being massless or massive.
Overview, FeynAmpDenominatorCombine.
amp = Get@FileNameJoin[{$FeynCalcDirectory, "Documentation",
"Examples", "Amplitudes", "Q-Q-massless-2L.m"}];FCReloadFunctionFromFile[FCLoopGetFeynAmpDenominators]All denominators depending on k1, k2
FCLoopGetFeynAmpDenominators[amp, {k1, k2}, denHead] // Last\left\{\text{denHead}\left(\frac{1}{(\text{k1}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{(\text{k1}^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{(\text{k2}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{(\text{k2}^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+\text{k2})^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+\text{k2})^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((-\text{k1}+\text{k2}+p)^2+i \eta )}\right)\right\}
All denominators depending on k1, k2 and the external momentum p
FCLoopGetFeynAmpDenominators[amp, {k1, k2}, denHead, Momentum -> {p}] // Last\left\{\text{denHead}\left(\frac{1}{((\text{k1}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((-\text{k1}+\text{k2}+p)^2+i \eta )}\right)\right\}
All denominators depending on k1, k2 and the external momentum p as well as massless denominators
FCLoopGetFeynAmpDenominators[amp, {k1, k2}, denHead, Momentum -> {p}, "Massless" -> True] // Last\left\{\text{denHead}\left(\frac{1}{(\text{k1}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{(\text{k2}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+\text{k2})^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}-\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k2}-p)^2-\text{mq}^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((\text{k1}+p)^2+i \eta )}\right),\text{denHead}\left(\frac{1}{((-\text{k1}+\text{k2}+p)^2+i \eta )}\right)\right\}