get_amplitude_rcl

get_amplitude_rcl(npr, order, colour, hel, pow=None, gs=None)

Extracts a specific contribution to the amplitude of the process with process number npr, according to the values of pow, order, colour and hel.

Parameters:
  • npr (int) – process number
  • order (str) –

    loop-order of the contribution

    • order = ‘LO’: tree squared amplitude
    • order = ‘NLO’: loop squared amplitude
    • order = ‘NLO-D4’: loop squared amplitude, bare loop contribution
    • order = ‘NLO-CT’: loop squared amplitude, counterterms contribution
    • order = ‘NLO-R2’: loop squared amplitude, rational terms contribution
  • colour (int[l]) – colour structure which is a vector of type integer and length l, where each position in the vector corresponds to one of the l external particles of process npr (ordered as in the process definition). For colourless particles, incoming quarks and outgoing anti-quarks, the corresponding entry in colour must be 0. For all other particles (gluons, outgoing quarks and incoming anti-quarks), the entries must be, without repetition, the positions of the gluons, incoming quarks and outgoing anti-quarks in the process definition.
  • hel (int[l]) –

    helicity (array) with entries:

    • left-handed fermions/antifermions: -1
    • right-handed fermions/antifermions: +1
    • logitudinal vector bosons: 0
    • transverse vector bosons: -1, +1
    • scalar particles: 0
  • pow/gs (int[]) – array with values representing the powers in fundamental couplings in the order as dictated by the model file, e.g. [2, 3] \(\equiv g_\mathrm{s}^2 e^3\), or, if supported by the model, the power in terms of \(g_\mathrm{s}\) only (power in \(e\) is determined automatically from the underlying process)
Returns:

(Ar, Ai)

Return type:

(float, float)