On W+W− production near threshold

Four-fermion production near the W pair-production threshold

“…Two-photon exchange is only a few-permille correction, confirming the expectation that Coulomb exchanges do not have to be summed to all orders due to the large width of the W boson. The one and two Coulomb-exchange terms have already been discussed in [10,11].…”

“…This corresponds to the one-loop diagram shown in Figure 2, computed with the vertex (13) and the propagator (10). We can use power counting to estimate the magnitude of the leading-order amplitude prior to its calculation.…”

“…In the numerical results below we will resum the full NLO width (81) in the effective-theory propagator (10), that is we do not perform an expansion of the propagator in the perturbative corrections to the matching coefficient ∆. We now describe how the formula for the NLO cross section must be modified to accomplish this summation of the width corrections.…”

“…This approximation was supposed to break down for kinematic reasons in the threshold region. Thus, when this project was begun [9], there existed only LO calculations in the threshold region as well as studies of the effect of Coulomb photon exchanges [10,11], rendering the effective field theory approach [12][13][14] the method of choice for the NLO calculation. Meanwhile a full NLO calculation of four-fermion production has been performed in the complex mass scheme [15,16] without any kinematic approximations, and for the fully differential cross sections in the continuum or near threshold.…”

Screened-Coulomb ansatz for the nonfactorizable radiative corrections to off-shell $W^+W^-$ production

“…Recall, that in the threshold and in the non-relativistic region the main contribution to the radiative corrections comes from the Coulomb interaction (see [5,12]). All other effects are suppressed by O(β).…”