Off-shell and non-factorizable effects in single-top hadroproduction
Pietro Falgari (Utrecht University)

Calculations involving massive unstable particles are very often performed in the so-called narrow-width approximation, in which the cross section is factorized into production and decay of an on-shell massive particle. In this approach off-shell effects and non-factorizable corrections, arising from interference of the production and decay subprocesses, are neglected. While these effects are known to be negligible for total cross sections, they could a priori be sizeable for an arbitrary observable involving several kinematical cuts, and thus relevant for hadron-collider phenomenology. In this talk I present NLO results for single-top production in hadron collisions which include the aforementioned off-shell and non-factorizable effects, thus extending earlier results beyond the narrow-width approximation. The calculation relies on effective-theory techniques and involves a simultaneous expansion of the amplitudes in powers of the couplings and of the virtuality p_t^2-mt^2 ~ Gamma_t/mt of the intermediate resonant top-quark. After a general introduction and illustration of the method I will discuss details of the calculation and present numerical results for the total cross section and a selection of kinematical distributions for single-top production at Tevatron and LHC.