ar X iv : h ep - p h / 02 10 13 0 v 1 8 O ct 2 00 2 YITP - SB - 02 - 56 Multi - loop Amplitudes and Resummation ⋆

ar X iv : h ep - p h / 02 10 13 0 v 2 1 0 O ct 2 00 2 YITP - SB - 02 - 56 Multi - loop Amplitudes and Resummation ⋆

We explore the relation between resummation and explicit multi-loop calculations for QCD hard-scattering amplitudes. We describe how the factorization properties of amplitudes lead to the exponentiation of double and single poles at each order of perturbation theory. For these amplitudes, previously-observed relations between single and double poles in different 2 → 2 processes can now be inter...

ar X iv : h ep - p h / 02 10 13 0 v 3 6 A pr 2 00 5 YITP - SB - 02 - 56 Multi - loop Amplitudes and Resummation ⋆

We explore the relation between resummation and explicit multi-loop calculations for QCD hard-scattering amplitudes. We describe how the factorization properties of amplitudes lead to the exponentiation of double and single poles at each order of perturbation theory. For these amplitudes, previously-observed relations between single and double poles in different 2 → 2 processes can now be inter...

ar X iv : h ep - p h / 02 11 28 0 v 1 1 8 N ov 2 00 2 Two - Loop Electroweak Corrections to ∆

The two-loop electroweak bosonic correction to the muon lifetime is computed using methods of asymptotic expansion. Combined with previous calculations this completes the full two-loop correction to ∆r in the Standard Model.

ar X iv : h ep - p h / 02 05 01 6 v 2 3 0 O ct 2 00 2 Scalar a 0 ( 980 ) meson in φ → π 0 ηγ decay

ar X iv : h ep - p h / 02 11 15 6 v 1 1 1 N ov 2 00 2 QCD two - loop amplitudes for e + e − → 3 jets : the fermionic contribution

We review a new technique for the calculation of two-loop amplitudes and discuss as an example the fermionic contributions to e + e − → q ¯ qg.