All-order results for soft and collinear gluons

I briefly review some general features and some recent developments concerning the resummation of long-distance singularities in QCD and in more general non-abelian gauge theories. I emphasize the field-theoretical tools of the trade, and focus mostly on the exponentiation of infrared and collinear divergences in amplitudes, which underlies the resummation of large logarithms in the corresponding cross sections. I then describe some recent results concerning the conformal limit, notably the case of N = 4 superymmetric Yang-Mills theoryComment: 15 pages, invited talk presented at the 10th Workshop in High Energy Physics Phenomenology (WHEPP X), Chennai, India, January 200

Updated Higgs cross section at approximate N3LO

We update our estimate of the cross section for Higgs production in gluon fusion at next- to-next-to-next-to-leading order (N3LO) in \u3b1s in view of the recent full computation of the result in the soft limit for infinite top mass, which determines a previously unknown constant. We briefly discuss the phenomenological implications. Results are available through the updated version of the ggHiggs code

The Ascomycete Verticillium longisporum Is a Hybrid and a Plant Pathogen with an Expanded Host Range

Hybridization plays a central role in plant evolution, but its overall importance in fungi is unknown. New plant pathogens are thought to arise by hybridization between formerly separated fungal species. Evolution of hybrid plant pathogens from non-pathogenic ancestors in the fungal-like protist Phytophthora has been demonstrated, but in fungi, the most important group of plant pathogens, there are few well-characterized examples of hybrids. We focused our attention on the hybrid and plant pathogen Verticillium longisporum, the causal agent of the Verticillium wilt disease in crucifer crops. In order to address questions related to the evolutionary origin of V. longisporum, we used phylogenetic analyses of seven nuclear loci and a dataset of 203 isolates of V. longisporum, V. dahliae and related species. We confirmed that V. longisporum was diploid, and originated three different times, involving four different lineages and three different parental species. All hybrids shared a common parent, species A1, that hybridized respectively with species D1, V. dahliae lineage D2 and V. dahliae lineage D3, to give rise to three different lineages of V. longisporum. Species A1 and species D1 constituted as yet unknown taxa. Verticillium longisporum likely originated recently, as each V. longisporum lineage was genetically homogenous, and comprised species A1 alleles that were identical across lineages

Soft gluons and hard scales in QCD: Heavy quarks at finite and all orders

The strong interaction of elementary particles is described by Quantum Chromodynamics (QCD). Utilizing this theory to describe and predict experimental data requires a number of concepts and techniques. Three of these, namely factorization, resummation and numerical phase space integration, are first reviewed and then applied here. Factorization into perturbative and non-perturbative contributions is an essential tool in understanding scattering processes involving hadrons. After reviewing factorization in a general context the concept is particularized and applied to derive resummation. Observables in strong interactions are usually expressed as series in the strong coupling constant. Resummation allows one to derive all-order, albeit still perturbative information on such observables. It is explained in which way such resummation calculation are closely related, and indeed dependent on factorization. Deep-inelastic charm production is presented as a process into which valuable insights can be gained through resummation, taking into account also the polarizations of the initial state particles. Whereas up to now resummation has been limited to those terms in the perturbation series kinematically dominant in some specific regions of phase space (e.g. near production thresholds), an extension of the method will be presented here to include also constant terms. In this context the discussion focusses on the Drell-Yan process. Finally, numerical phase space integrations are investigated for a process involving the production of strongly interacting heavy final state particles. Here two methods, namely the phase space slicing and the dipole subtraction methods, are explained and compared as to their numerical performances

HERA and the LHC - A workshop on the implications of HERA for LHC physics: Proceedings Part A

The HERA electron--proton collider has collected 100 pb$^{-1}$ of data since its start-up in 1992, and recently moved into a high-luminosity operation mode, with upgraded detectors, aiming to increase the total integrated luminosity per experiment to more than 500 pb$^{-1}$. HERA has been a machine of excellence for the study of QCD and the structure of the proton. The Large Hadron Collider (LHC), which will collide protons with a centre-of-mass energy of 14 TeV, will be completed at CERN in 2007. The main mission of the LHC is to discover and study the mechanisms of electroweak symmetry breaking, possibly via the discovery of the Higgs particle, and search for new physics in the TeV energy scale, such as supersymmetry or extra dimensions. Besides these goals, the LHC will also make a substantial number of precision measurements and will offer a new regime to study the strong force via perturbative QCD processes and diffraction. For the full LHC physics programme a good understanding of QCD phenomena and the structure function of the proton is essential. Therefore, in March 2004, a one-year-long workshop started to study the implications of HERA on LHC physics. This included proposing new measurements to be made at HERA, extracting the maximum information from the available data, and developing/improving the theoretical and experimental tools. This report summarizes the results achieved during this workshop.Comment: Part A: plenary presentations, WG1: parton density functions, WG2: Multi-Jet final states and energy flows. 326 pages Part B: WG3: Heavy Quarks (Charm and Beauty), WG4: Diffraction, WG5: Monte Carlo Tools, 330 page