Developments in perturbative QCD.pdfVIP

a r X i v : h e p - p h / 0 5 1 0 0 9 0 v 2 1 7 O c t 2 0 0 5 DEVELOPMENTS IN PERTURBATIVE QCD GAVIN P. SALAM LPTHE, Universities of Paris VI and VII and CNRS UMR 7589, Paris, France. A brief review of key recent developments and ongoing projects in perturbative QCD theory, with emphasis on conceptual advances that have the potential for impact on LHC studies. Topics covered include: twistors and new recursive calculational techniques; automation of one-loop predictions; developments concerning NNLO calculations; the status of Monte Carlo event generators and progress in matching to fixed order; analytical resummation including the push to NNLL, automation and gap between jets processes; and progress in the understanding of saturation at small x. 1 Introduction A significant part of today’s research in QCD aims to provide tools to help bet- ter constrain the standard model and find what may lie beyond it. For example one wishes to determine, as accurately as possi- ble, the fundamentals of the QCD and elec- troweak theories, such as αs, quark masses, and the elements of the CKM matrix. One also needs precise information about ‘pseudo- fundamentals,’ quantities such as parton dis- tribution functions (PDFs) that could be predicted if we knew how to solve non- perturbative QCD, but which currently must be deduced from experimental data. Finally, one puts this information together to predict the QCD aspects of both backgrounds and signals at high energy colliders, particularly at the Tevatron and LHC, to help maximise the chance of discovering and understanding any new physics. Other facets of QCD research seek to ex- tend the boundaries of our knowledge of QCD itself. The underlying Yang-Mills field theory is rich in its own right, and unexpected new perturbative structures have emerged in the past two years from considerations of string theory. In the high-energy limit of QCD it is believed that a new state appears, the widely studied colour glass condensate, wh