NLO QCD calculations with HELAC-NLO

Achieving a precise description of multi-parton final states is crucial for many analyses at LHC. In this contribution we review the main features of the HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections for tt + 2 jet production at LHC are illustrated and discussed.Comment: 7 pages, 4 figures. Presented at 10th DESY Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory, Worlitz, Germany, April 25-30, 201

Counting to one: reducibility of one- and two-loop amplitudes at the integrand level

Calculation of amplitudes in perturbative quantum field theory involve large loop integrals. The complexity of those integrals, in combination with the large number of Feynman diagrams, make the calculations very difficult. Reduction methods proved to be very helpful, lowering the number of integrals that need to be actually calculated. Especially, the reduction at the integrand level technique, improves the speed and set-up of these calculations. In this article we demonstrate, by counting the numbers of tensor structures and independent coefficients, how to write such relations at the integrand level for one- and two-loop amplitudes. We clarify their connection to the so-called spurious terms at one loop and discuss their structure in the two-loop case. This method is also applicable to higher loops, and the results obtained apply to both planar and non-planar diagrams

Investigation of the Retention Mechanism of Cephalosporins by Zwitterionic Hydrophilic Interaction Liquid Chromatography

The importance of cephalosporin antibiotics in medicine requires the development of high performance separation methods for their analysis. In this paper cefazolin, cefuroxime, cefoxitin, cefaclor and ceftriaxone were used as model compounds to investigate the retention mechanism under zwitterionic HILIC conditions. The analysis was performed using a ZIC®-HILIC analytical column (150.0 × 2.1 mm i.d., particle size 3.5 μm, 200 Å) with isocratic elution. The mobile phase was a mixture of acetonitrile and ammonium acetate or formate buffer. To get a better insight into the retention mechanism on ZIC®-HILIC columns the main factors influencing the retention and selectivity of the analytes have been thoroughly investigated. It is shown that the type of the salt and its concentration along with the volume fraction of water in the mobile phase and pH of the aqueous buffer greatly affect the retention of the tested cephalosporins due to their structures and physicochemical properties. The method was applied successfully to the analysis of injection dosage forms containing cefazolin, cefuroxime and cefoxitin. © 2016, Springer-Verlag Berlin Heidelberg