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We compute for the first time the so-called complete NLO corrections to top-quark pair production with one and two isolated photons in the di-lepton top-quark decay channel. The Narrow Width Approximation is used for the modeling of unstable top quarks and W bosons. Higher-order QCD and EW effects as well as photon bremsstrahlung are consistently included at all stages: in production and top-quark decays. We present results at the integrated and differential fiducial cross-section level for both processes for the LHC Run II center-of-mass energy of s=13 TeV. In addition, we investigate the scale choice in photonic observables. Finally, the individual size of each subleading contribution is discussed in detail and the origin of the main subleading corrections is scrutinised. For the latter case, alternative calculations are performed in which the subleading NLO corrections are included only in the production of tt and tt.
Stremmer et al. (Wed,) studied this question.