Aspects of the structure and phenology of two fynbos communities

Data on the floristics, biomass, pattern, growth forms and regeneration modes of two tall, mid-dense, proteoid shrublands are analysed. The phenology of a number of species in different growth forms is examined in terms of current hypotheses about growth form related timing of shoot growth, and general patterns of periodicity in nutrient-poor mediterranean environments. Taxa typical of the fynbos flora are dominant in both communities, but the drier Cedarberg community has fewer species in these taxa and more annuals than the moister Kogelberg environment. These floristic changes are reflected also in the growth form spectra and the stratification of the communities. The biomass of the cedarberg community is higher at 1820 g/m2 against 1100 g/m2 for the Kogelberg community. This difference is discussed in terms of the greater effectiveness of the rainfall at the Cedarberg (664 mm/yr), than at the Kogelberg (1016 mm/yr), and the availability of soil nutrients. There are more sprouting plants, excluding annuals, in the flora of the Cedarberg site. This is in line with the prediction that, within limits, the drier the climate, the more reliable the investment in vegetative regrowth after fire. The similarity in community physiognomy is confirmed by the quantitative analyses which show that there are differences and also strong similarities between the communities. The overstorey Proteaceae grow from spring to mid-summer, as do the Restionaceae, but the other growth forms follow a variety of patterns, including opportunistic summer growth. The sequence of phenological events is partly related to morphological sequences in plant development and partly to resource partitioning. The current hypotheses concerning community structure and phenology in mediterranean environments cannot be refuted, but they do not account for the variations observed within and between growth forms and need to be critically examined

Two-Loop QCD Corrections to the Heavy-to-Light Quark Decay

We present an analytic expression for the two-loop QCD corrections to the decay process b -> u W^*, where b and u are a massive and massless quark, respectively, while W^* is an off-shell charged weak boson. Since the W-boson can subsequently decay in a lepton anti-neutrino pair, the results of this paper are a first step towards a fully analytic computation of differential distributions for the semileptonic decay of a b-quark. The latter partonic process plays a crucial role in the study of inclusive semileptonic charmless decays of B-mesons. The three independent form factors characterizing the b W u vertex are provided in form of a Laurent series in (d-4), where d is the space-time dimension. The coefficients in the series are expressed in terms of Harmonic Polylogarithms of maximal weight 4, and are functions of the invariant mass of the leptonic decay products of the W-boson.Comment: 27 pages, 3 figures, References added, version published on JHE

Next-to-Leading Order Jet Physics with BlackHat

We present several results obtained using the BlackHat next-to-leading order QCD program library, in conjunction with SHERPA. In particular, we present distributions for vector boson plus 1,2,3-jet production at the Tevatron and at the asymptotic running energy of the Large Hadron Collider, including new Z+3-jet distributions. The Z+2-jet predictions for the second-jet P_T distribution are compared to CDF data. We present the jet-emission probability at NLO in W+2-jet events at the LHC, where the tagging jets are taken to be the ones furthest apart in pseudorapidity. We analyze further the large left-handed W polarization, identified in our previous study, for W bosons produced at high P_T at the LHC.Comment: Presented at RADCOR 2009 - 9th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), October 25 - 30 2009, Ascona, Switzerland}, 12 pages, 9 figures, LaTeX, v2 updated small correction to polarization effect plo

Multi-jet cross sections at NLO with BlackHat and Sherpa

In this talk, we report on a recent next-to-leading order QCD calculation of the production of a W boson in association with three jets at hadron colliders. The computation is performed by combining two programs, BlackHat for the computation of the virtual one-loop matrix elements and Sherpa for the real emission part.Comment: 4 pages, contribution to the proceedings of the XLIIIth Rencontres de Moriond (QCD

The BlackHat Library for One-Loop Amplitudes

We present recent next-to-leading order (NLO) results in perturbative QCD obtained using the BlackHat software library. We discuss the use of n-tuples to separate the lengthy matrix-element computations from the analysis process. The use of n-tuples allows many analyses to be carried out on the same phase-space samples, and also allows experimenters to conduct their own analyses using the original NLO computation.Comment: Talk given at ACAT 2013, Beijing, China, May 16--21, 2013; 6 pages, 2 figures; added reference

Universality in W+Multijet Production

We study $W$-boson production accompanied by multiple jets at 7 TeV at the LHC. We study the jet-production ratio, of total cross sections for $W$+$n$- to $W$+($n-1$)-jet production, and the ratio of distributions in the total transverse hadronic jet energy $H_{\rm T}^{\rm jets}$. We use the ratios to extrapolate the total cross section, and the differential distribution in $H_{\rm T}^{\rm jets}$, to $W$+6-jet production. We use the BlackHat software library in conjunction with SHERPA to perform the computations.Comment: Merge of Moriond 2014 and Loops & Legs 2014 proceedings, 6 pages, 2 figure