R E C O L A—REcursive Computation of One-Loop Amplitudes

109

Abstract:We calculate the complete-NLO predictions for ttW ± and tttt production in proton-proton collisions at 13 and 100 TeV. All the non-vanishing contributions of O(α i s α j ) with i + j = 3, 4 for ttW ± and i + j = 4, 5 for tttt are evaluated without any approximation. For ttW ± we find that, due to the presence of tW → tW scattering, at 13(100) TeV the O(α s α 3 ) contribution is about 12(70)% of the LO, i.e., it is larger than the so-called NLO EW corrections (the O(α 2 s α 2 ) terms) and has opposite sign. In the case of tttt production, large contributions from electroweak tt → tt scattering are already present at LO in the O(α 3 s α) and O(α 2 s α 2 ) terms. For the same reason we find that both NLO terms of O(α 4 s α), i.e., the NLO EW corrections, and O(α 3 s α 2 ) are large (±15% of the LO) and their relative contributions strongly depend on the values of the renormalisation and factorisation scales. However, large accidental cancellations are present (away from the threshold region) between these two contributions. Moreover, the NLO corrections strongly depend on the kinematics and are particularly large at the threshold, where even the relative contribution from O(α 2 s α 3 ) terms amounts to tens of percents.

Section: Jhep02(2018)031mentioning

confidence: 99%

Large NLO corrections in t t ¯ W ± $$ t\overline{t}{W}^{\pm } $$ and

Frederix

Pagani

Zaro

2018

109

“…In detail, the calculation proceeds diagrammatically, starting with the generation of Feynman diagrams with FeynArts [55,56] and further algebraic processing with in-house Mathematica routines. The other calculation has been carried out with the program Recola [48,49] facilitating the automated generation of NLO EW amplitudes, in combination with an in-house Monte Carlo generator. Additional checks have been performed employing the Mathematica package Pole [57], which internally makes use of FeynArts [55,56] and FormCalc [58,59].…”

Section: Jhep06(2016)065mentioning

confidence: 99%

“…One of our matrix-element calculations follows exactly the strategy of refs. [42,43], the other one is based on Recola [48,49]. To obtain numerically stable results for the loop integrals everywhere in phase space, we use the library Collier [50,51].…”

Section: Jhep06(2016)065mentioning

confidence: 99%

Next-to-leading-order electroweak corrections to pp → W+W− → 4 leptons at the LHC

Biedermann

Billoni

Denner

et al. 2016

We present results of the first calculation of next-to-leading-order electroweak corrections to W-boson pair production at the LHC that fully takes into account leptonic W-boson decays and off-shell effects. Employing realistic event selections, we discuss the corrections in situations that are typical for the study of W-boson pairs as a signal process or of Higgs-boson decays H → WW * , to which W-boson pair production represents an irreducible background. In particular, we compare the full off-shell results, obtained treating the W-boson resonances in the complex-mass scheme, to previous results in the so-called double-pole approximation, which is based on an expansion of the loop amplitudes about the W resonance poles. At small and intermediate scales, i.e. in particular in angular and rapidity distributions, the two approaches show the expected agreement at the level of fractions of a percent, but larger differences appear in the TeV range. For transverse-momentum distributions, the differences can even exceed the 10% level in the TeV range where "background diagrams" with one instead of two resonant W bosons gain in importance because of recoil effects.

“…This has been made possible by tremendous advances in the automation of the computation of one-loop amplitudes during the last decade. Publicly available one-loop providers (OLPs) such as Helac-1Loop [44], OpenLoops [45], GoSam [46], Recola [47,48] or MadLoop [49] can compute arbitrary virtual matrix elements in the SM, though in practice limited by JHEP12(2016)075 computing power. Complete NLO QCD support has so far been achieved within the frameworks of Helac-NLO [50], Madgraph5 aMC@NLO [51], Sherpa [52] and Herwig7 [53].…”

Section: Jhep12(2016)075mentioning

confidence: 99%

NLO QCD predictions for off-shell t t ¯ $$ t\overline{t} $$ and t t ¯ H $$ t\overline{t}H $$ production and decay at a linear collider

Nejad¹,

Kilian²,

Lindert

et al. 2016

We present predictions for tt and ttH production and decay at future lepton colliders including non-resonant and interference contributions up to next-to-leading order (NLO) in perturbative QCD. The obtained precision predictions are necessary for a future precise determination of the top-quark Yukawa coupling, and allow for top-quark phenomenology in the continuum at an unprecedented level of accuracy. Simulations are performed with the automated NLO Monte-Carlo framework Whizard interfaced to the OpenLoops matrix element generator.