Pietro Falgari

Four-fermion production near the W pair-production threshold

Abstract We perform a dedicated study of the four-fermion production process e − e + → μ − ν ¯ μ u d ¯ X near the W pair-production threshold in view of the importance of this process for a precise measurement of the W boson mass. Accurate theoretical predictions for this process require a systematic treatment of finite-width effects. We use unstable-particle effective field theory (EFT) to perform an expansion in the coupling constants, Γ W / M W , and the non-relativistic velocity v of the W boson up to next-to-leading order in Γ W / M W ∼ α ew ∼ v 2 . We find that the dominant theoretical uncertainty in M W is currently due to an incomplete treatment of initial-state radiation. The remaining uncertainty of the NLO EFT calculation translates into δ M W ≈ 10 – 15 MeV , and to about 5 MeV with additional input from the NLO four-fermion calculation in the full theory.

BFKL at next-to-next-to-leading order

We determine an approximate expression for the O(� 3 ) contribution �2 to the kernel of the BFKL equation, which includes all collinear and anticollinear singular contributions. This is derived using recent results on the relation between the GLAP and BFKL kernels (including running-coupling effects to all orders) and on small-x factorization schemes. We present the result in various schemes, relevant both for applications to the BFKL equation and to small-x evolution of parton distributions.

Dominant NNLO corrections to four-fermion production near the W-pair production threshold

Abstract We calculate the parametrically dominant next-to-next-to-leading order corrections to four-fermion production e − e + → μ − ν ¯ μ u d ¯ + X at centre-of-mass energies near the W -pair production threshold employing the method of unstable-particle effective theory. In total the correction is small, leading to a shift of 3 MeV in the W -mass measurement. We also discuss the implementation of realistic cuts and provide a result for the interference of single-Coulomb and soft radiative corrections that can easily be extended to include an arbitrary number of Coulomb photons.

Higher-order soft and Coulomb corrections to squark and gluino production at the LHC

We present predictions for the total cross sections for pair production of squarks and gluinos at the LHC including a combined NNLL resummation of soft and Coulomb gluon effects. The NNLL corrections can be up to 25% relative to previous NLL results and reduce the theoretical uncertainties to the 10% level.

All-order colour structure and two-loop anomalous dimension of soft radiation in heavy particle pair production at the LHC

We consider the factorization and resummation of soft and Coulomb gluons for pair-production processes of heavy coloured particles at hadron colliders, and discuss: the construction of a colour basis that diagonalizes the leading soft function to all orders in perturbation theory; the determination of the two-loop soft anomalous dimension needed for NNLL resummations; and a general formula that provides all logarithmically enhanced O(α2 s ) correction requiring as processindependent input only the one-loop hard matching coefficients.

Resonant Particle Production at Hadron Colliders

We present a method to compute off-shell effects for processes involving resonant particles at hadron colliders with the possibility to include realistic cuts on the decay products. The method is based on an effective theory approach to unstable particle production and, as an example, is applied to t-channel single top production at the LHC.