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 ⋆

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 ⋆

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 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 10 07 4 v 1 4 O ct 2 00 2 Effective vertex for π 0 γγ §

The π 0 γγ vertex is used as an explicit example of the subtleties connected with the application of equation of motion within Chiral Perturbation Theory at the order O(p 6).

ar X iv : h ep - p h / 06 02 02 0 v 1 2 F eb 2 00 6 Automated Resummation and Hadron Collider Event Shapes ∗

whereHmn are numerical coefficients and we have introduced the shorthand L ≡ ln 1/v. The double logarithms are associated with non-cancellation between soft and collinear divergences in real and virtual graph, since limiting v suppresses real radiation but not the corresponding virtual terms. When v is small (ln v ∼ α s ) all terms αs L 2m become of the same magnitude (∼ 1) and reliable calcula...