Alpha_s: from DIS to LEP

The strong coupling alpha_s is a fundamental parameter of the Standard Model. In comparison to parameters like alpha_em and M_Z it is relatively poorly known. However the precision of alpha_s measurements has improved dramatically in recent years. More than twenty different types of process, from lattice QCD studies to the highest energy colliders, can be used to measure alpha_s accurately. The most precise determinations now quote uncertainties in alpha_s(M_Z) of less than 5%. There is also a remarkable consistency between the various measurements. The present review provides an update on alpha_s measurements from the past year.Comment: 12 pages LaTeX and 4 encapsulated postscript figures, using epsfig and (modified) l-school macros. Based on a talk presented at the conference on New Non-Perturbative Methods and Quantisation on the Light Cone, Les Houches, March 199

On the Resummation of Subleading Logarithms in the Transverse Momentum Distribution of Vector Bosons Produced at Hadron Colliders

The perturbation series for electroweak vector boson production at small transverse momentum is dominated by large double logarithms at each order in perturbation theory. An accurate theoretical prediction therefore requires a resummation of these logarithms. This can be performed either directly in transverse momentum space or in impact parameter (Fourier transform) space. While both approaches resum the same leading double logarithms, the subleading logarithms are, in general, treated differently. We comment on two recent approaches to this problem, emphasising the particular subleading logarithms resummed in each case and the numerical differences in the cross sections which result.Comment: 13 (Latex) pages, including 5 embedded figures, uses epsfig.st

Electroweak gauge boson polarisation at the LHC

We study the polarisation of gauge bosons produced at the LHC. Polarisation effects for W bosons manifest themselves in the angular distributions of the lepton and in the distributions of lepton transverse momentum and missing transverse energy. The distributions also depend on the selection cuts, with kinematic effects competing with polarisation effects. The polarisation is discussed for a range of different processes producing W bosons: W+jets, W from top (single and pair) production, W pair production and W production in association with a Z or Higgs boson. The relative contributions of the different polarisation states varies from process to process, reflecting the dynamics of the underlying hard-scattering process. We also present results for the polarisation of the Z boson produced in association with QCD jets at the LHC, and comment on the differences between W and Z production.Comment: 27 pages, 25 figure

BFKL Physics in Jet Production at e+e- colliders

Virtual photon scattering in $e^+e^-$ collisions can result in events with the electron-positron pair at large rapidity separation with hadronic activity in between. The BFKL equation resums large logarithms that dominate the cross section for this process. We report here on a Monte Carlo method for solving the BFKL equation that allows kinematic constraints to be taken into account and show results for $e^+e^-$ collisions.Comment: 3 pages, Latex, talk presented at the 2000 Meeting of the Division of Particles and Fields of the APS, Columbus, OH, August 9--12, 200