Automated one-loop calculations with GoSam

Abstract

We present the program package GOSAM which is designed for the automated calculation of one-loop amplitudes for multi-particle processes in renormalisable quantum field theories. The amplitudes, which are generated in terms of Feynman diagrams, can be reduced using either D-dimensional integrand-level decomposition or tensor reduction. GOSAM can be used to calculate one-loop QCD and/or electroweak corrections to Standard Model processes and offers the flexibility to link model files for theories Beyond the Standard Model. A standard interface to programs calculating real radiation is also implemented. We demonstrate the flexibility of the program by presenting examples of processes with up to six external legs attached to the loop.

Scaling patterns for QCD jets

“…However, over the past few years this field has progressed enormously. As a consequence for Standard Model processes a similar level of automation as for leadingorder calculations is within reach [34][35][36][37][38][39][40][41][42][43]. An approach applicable for general New Physics extensions, though limited to 2 → 2 processes, has been presented in [44,45].…”

Electroweak corrections to lepton pair production in association with two hard jets at the LHC

“…In the past years, many groups have concentrated their efforts to make NLO calculations feasible, and a lot of codes have been designed [3][4][5][6][7][8][9][10][11] with a high level of automatisation and impressive performances, however with their range of applicability mostly restricted to the QCD sector of the SM. For EW corrections, the situation is more involved and a complete automatisation has not been achieved yet, while different groups are working in this direction [12,13].…”

“…Denoting the momenta of the incoming partons by k 1 , k 2 and the final-state momenta by k i = {k j 1 , k j 2 , k ℓ − , k ℓ + }, the LO cross section σ LO is obtained as 10) where dP(x i ) incorporates the convolution with the parton distributions functions, dΦ(k i ) represents the phase space measure, and Θ cut (k i ) defines the acceptance function.…”

Soft evolution of multi-jet final states

“…Equation (2.12) reduces to 13) where the sum runs over only (n − 2)! permutations, corresponding to the new basis elements.…”

“…Next-to-leading order (NLO) corrections have also reached a high level of automation [7][8][9][10][11][12][13][14][15][16][17], and fully differential multi-jet cross…”