Large NLO corrections in t(t)over-barW± and t(t)over-bart(t)over-bar hadroproduction from supposedly subleading EW contributions

We calculate the complete-NLO predictions for t (t) over barW(+/-) and t (t) over bart (t) over bar production in proton-proton collisions at 13 and 100TeV. All the non-vanishing contributions of O (alpha(i)(s)alpha(j)) with i + j = 3, 4 for t (t) over barW (+/-) and i + j = 4, 5 for t (t) over bart (t) over bar are evaluated without any approximation. For t (t) over barW(+/-) we find that, due to the presence of tW -> tW scattering, at 13(100) TeV the O (alpha(s)alpha(3)) contribution is about 12(70)% of the LO, i.e., it is larger than the so-called NLO EW corrections (the O (alpha(2)(s)alpha(2)) terms) and has opposite sign. In the case of t (t) over bart (t) over bar production, large contributions from electroweak tt -> tt scattering are already present at LO in the O (alpha(3)(s)alpha) and O (alpha(2)(s)alpha(2)) terms. For the same reason we fi nd that both NLO terms of O(alpha(4)(s)alpha), i.e., the NLO EW corrections, and O(alpha(3)(s)alpha(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(alpha(3)(s)alpha(2)) terms amounts to tens of percents.