Improving predictions for associated ttˉHt\bar{t} H production at the LHC : soft gluon resummation through NNLL accuracy

In the following we present our recent results on the resummation of soft gluon corrections to the $pp\rightarrow t\bar{t}H$ cross section at the LHC. The resummation was carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the Mellin space technique. Obtained results were matched to the NLO cross section. We show that the resummation leads to reduction of scale-variation uncertainty of the total $pp\rightarrow t\bar{t}H$ cross section.Comment: 6 pages, 1 figure, 1 table, proceedings prepared for the European Physical Society Conference on High Energy Physics (EPS-HEP 2017), 5-12 July 2017, Venice, Ital

Associated ttˉHt \bar{t} H production at the LHC: theoretical predictions at NLO+NNLL accuracy

We perform threshold resummation of soft gluon corrections to the total cross section and the invariant mass distribution for the process $pp \to t\bar{t}H$. The resummation is carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the direct QCD Mellin space technique in the three-particle invariant mass kinematics. After presenting analytical expressions we discuss the impact of resummation on the numerical predictions for the associated Higgs boson production with top quarks at the LHC. We find that NLO+NNLL resummation leads to predictions for which the central values are remarkably stable with respect to scale variation and for which theoretical uncertainties are reduced in comparison to NLO predictions.Comment: 21 pages, 9 figures; NNLL results accounting now for color decomposition of the one-loop hard function, discussion of the literature added, typos correcte

Soft gluon resummation for associated ttˉHt \bar{t} H production at the LHC

We perform resummation of soft gluon corrections to the total cross section for the process $pp \to t\bar{t}H$. The resummation is carried out at next-to-leading-logarithmic (NLL) accuracy using the Mellin space technique, extending its application to the class of $2 \to 3$ processes. We present an analytical result for the soft anomalous dimension for a hadronic production of two coloured massive particles in association with a colour singlet. We discuss the impact of resummation on the numerical prediction for the associated Higgs boson production with top quarks at the LHC.Comment: 11 pages, 4 figure

Soft gluon resummation for the associated production of a top quark pair with a W boson at the LHC

We present our results on soft gluon resummation in the invariant mass threshold applied to the associated production of a top quark pair with a W boson at the LHC in the Mellin space formalism.Comment: 6 pages, 4 figures, 1 table, proceedings prepared for the European Physical Society Conference on High Energy Physics (EPS-HEP 2017), 5-12 July 2017, Venice, Ital

Associated top-pair production with a heavy boson production through NLO+NNLL accuracy at the LHC

In this talk we present results of our recent calculations of cross sections and distributions for the associate production of top-antitop quark pairs with a heavy boson (Higgs, W, Z) at the LHC, obtained using threshold resummation in direct QCD, i.e. in the Mellin-space approach.Comment: 4 pages, 6 figures, contribution to the 2019 QCD session of the 54th Rencontres de Morion

A study of the interrelationships of some Natal species of Senecio (Asteraceae/Compositae)

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.This dissertation presents the results of studies of the generic concept of Senecio and the subsequent testing of the hypothes is: that many of the species of Senecio in Natal are congeneric with Senecio L. sensu stricto. The sample of taxa studied consisted of 87 Natal senecios, 5 Cape heterochromous senecios and 10 non-southern African senecios, including the type of the genus, S. vulgaris L. Also included in the study were 5 species from taxonomically closely related genera in the tribe Senecioneae and two senecios of uncertain taxonomic position. The phenotype of these taxa was investigated with respect to a large number of morphological and micromorphological characters (126) and the data obtained were analysed neurally and numerically. Aspects of the pollen micromorphology, of all the taxa studied, were also investigated using the scanning electron microscope. A review of the chemical complement of all the taxa studied. particularly with respect to terpenes and pyrrolizidine alkaloids, was also undertaken. Six characters were selected as being taxonomically significant with respect to elucidating the generic concept of Senecio. A further 31 characters and the aforementioned 6, were selected as .being taxonomically significant with respect to elucidating the interrelationships of the Natal senecios and all the senecios studied. The generic concept of Senecio has been re-circumscribed and the generic status of each of the senecios studied has been tested according to this concept of Senecio sensu Vincent. In the light of my concept of Senecio, the following species are excluded from Senecio sensu Vincent: S. barbertonicus Klatt, S. cissampelinus (DC.) Schultz Bipontinus, S. fulgens (J.D. Hooker) Nicholson, S. helminthioides (Schultz Bipontinus) Hilliard, S. hockii De Wild. & Muschl., S. medley-woodii Hutchinson, S. radicans (L.L) Schultz Bipontinus, S. syringifolius O.Hoffm., S. tamoides DC., S. transvaalensis Bolus and S. viminalis Bremekamp. Senecio brevilorus Hilliard, S. seminiveus Wood & Evans and S. tanacetopsis Hilliard are considered to be peripheral to Senecio s. str. sensu Vincent, and are included in Senecio s. lat. sensu Vincent. The hypothesis regarding the generic status of the Natal senecios has been accepted, subsequent to the circumscription of Senecio s. str. sensu Vincent. Estimates of the phenetic affinity of all the members of Senecio sensu stricto sensu Vincent, included in this study, have been made. The majority of the Natal senecios, while clearly being members of Senecio s. str. sensu Vincent, are distinct from virtually all the Cape and non-southern African senecios studied. Many of the non-yellow (purple) Natal senecios form clearly allied groups which are distinct from the groups (clusters) composed of yellow senecios. The taxonomic position of several taxa is questioned, in the light of the cluster analyses. The evidence from the palynological studies neither contradicts nor supports the proposed infrageneric interrelationships, with respect to the Natal members of Senecios. str. sensu Vincent. The evidence also neither contradicts nor supports the proposed interrelationships between the Natal, the Cape and the non-southern African members of Senecios. str. sensu Vincent. The terpene and pyrrolizidine chemistry of many of many of the senecios studied is characterised by the presence of furanoeremophilanes. Eremophilanes also occur and are particularly associated with a number of non-yellow (purple) senecios. Pyrrolizidine alkaloids are not ubiquitous amongst the senecios studied, while some senecios appear to only synthesise pyrrolizidine alKaloids. The review of the errpene and pyrrolizidine chemistry of the senecios investigated, illustrates how our knowledge at or near the level of analytic characters is far from complete. However, we have definitely progressed from the synthetic level of character use. Nevertheless, the relationships between the members of Senecios. str. sensu Vincent, could not be evaluated in the light of the individual chemical complement of terpenes and pyrrolizidine alkaloids, because of a lack of information. An hypothesis of the chemical evolution within the Senecioneae is tested with in Senecios. str. sensu Vincent . Before any taxonomic changes are made to t he current composition of Senecio L., the concept of Senecio L. s. str. sensu Vincent, needs to be tested against a far wider sample of the genus

Top Precision for Associated Top-Pair Production Processes at the LHC

The studies of the associated production processes of a top-quark pair with a colour-singlet boson, e.g. Higgs, W or Z, are among the highest priorities of the LHC programme. Correspondingly, improvements in precision of theoretical predictions for these processes are of central importance. In this talk, we review our latest results on resummation of soft gluon corrections. The resummation is carried out using the direct QCD Mellin space technique in three-particle invariant mass kinematics. We discuss the impact of the soft gluon corrections on predictions for total cross sections and differential distributions.Comment: 12 pages, 9 figures, proceedings of the XXVI Cracow Epiphany Conference on LHC Physics: Standard Model and Beyond, to be published in Acta Physica Polonica

Associated top quark pair production with a heavy boson: differential cross sections at NLO+NNLL accuracy

We present theoretical predictions for selected differential cross sections for the process $pp \to t \bar{t} B$ at the LHC, where $B$ can be a Higgs ($H$), a $Z$ or a $W$ boson. The predictions are calculated in the direct QCD framework up to the next-to-next-leading logarithmic (NNLL) accuracy and matched to the complete NLO results including QCD and electroweak effects. Additionally, results for the total cross sections are provided. The calculations deliver a significant improvement of the theoretical predictions, especially for the $t \bar{t} H$ and the $t \bar{t} Z$ production. In these cases, predictions for both the total and differential cross sections are remarkably stable with respect to the central scale choice and carry a substantially reduced scale uncertainty in comparison with the complete NLO predictions.Comment: 28 pages, 23 figures; Published versio

Efficient singlet oxygen photogeneration by zinc porphyrin-dimers upon one- and two-photon excitation

Funding: UK EPSRC (EP/L017008/1), IDWS acknowledges a Royal Society Wolfson Research Merit Award. This work is a part of the ITN-EJD-2017 project POLYTHEA which has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement 764837.The development of photodynamic therapy at depth requires photosensitizers which have both sufficient quantum yield for singlet oxygen generation and strong two photon absorption. Here we show that this can be achieved by conjugated linkage of zinc porphyrins to make dimers. We determined the quantum yield of generation of 1O2, φΔ , by measuring emission at 1270 nm using a near infra-red streak camera and found it to increase from 15% for a single porphyrin unit to 27 47% for the dimers with a conjugated linker. Then, we measured the spectra of two-photon absorption cross section, σ2, by a focus-tunable Z scan method, which allows for nondestructive investigation of light-sensitive materials. We observed a strong enhancement of the two photon absorption coefficient in the dimers, especially those with an alkyne linker. These results lead to an excellent figure of merit for two photon production of singlet oxygen (expressed by the product σ2xφΔ) in the porphyrin dimers, of around 3700 GM, which is very promising for applications involving treatment of deep tumors by photodynamic therapy.PostprintPeer reviewe