Loop-tree duality and quantum field theory in four dimensions

Loop-tree duality allows to express virtual contributions in terms of phase-space integrals, thus leading to a direct comparison with real radiation terms. In this talk, we review the basis of the method and describe its application to regularize Feynman integrals. Performing an integrand-level combination of real and virtual terms, we obtain finite contributions that can be computed in four-dimensions. Moreover, this method provides a natural physical interpretation of infrared singularities, their origin and the way that they cancel in the complete computation.Comment: 10 pages, 1 figure. Contribution to the Proceedings of the 12th International Symposium on Radiative Corrections (Radcor 2015) and LoopFest XIV (Radiative Corrections for the LHC and Future Colliders

QED corrections to the Altarelli-Parisi splitting functions

We discuss the combined effect of QED and QCD corrections to the evolution of parton distributions. We extend the available knowledge of the Altarelli-Parisi splitting functions to one order higher in QED, and provide explicit expressions for the splitting kernels up to ${\cal O}(\alpha \, \alpha_{\mathrm{S}})$. The results presented in this article allow to perform a parton distribution function analysis reaching full NLO QCD-QED combined precision.Comment: 11 pages, 1 figure. References added, improved discussion. Final version published in EPJC. Typo corrected in Eq. (22

Higher-order QED effects in hadronic processes

In this presentation, we describe the computation of higher-order QED effects relevant in hadronic collisions. In particular, we discuss the calculation of mixed QCD-QED one-loop contributions to the Altarelli-Parisi splittings functions, as well as the pure two-loop QED corrections. We explain how to extend the DGLAP equations to deal with new parton distributions, emphasizing the consequences of the novel corrections in the determination (and evolution) of the photon distributions.Comment: 7 pages, 2 figures. Contribution to the Proceedings of the EPS-HEP 2017 Conferenc

Beyond the happy sheets! Evaluating learning in information skills teaching

This paper reviews three years of data measuring students' immediate reactions to a computer-assisted learning package in information skills and reports on work in progress to establish a more comprehensive programme of evaluation which will assess the longer term impact on learning of both the courseware itself and the way the courseware is delivered to students. The GAELS courseware was developed in the late 1990s as part of a collaborative project between the Universities of Glasgow and Strathclyde, with funding from the Scottish Higher Education Funding Council. The courseware was designed to teach higher level information skills and was initially developed for use with postgraduate engineering students; it has subsequently been adapted for use with students in other subject areas, including biological and physical sciences, and has been embedded for several years now in workshop sessions undertaken with postgraduate and undergraduate students across the Faculties of Science and Engineering at the University of Strathclyde. The courseware is introduced at the start of the academic session and made available on the Web so that students can use it as needed during their course and project work. During the first year, the courseware was used in isolation from other teaching methods (although a librarian was present to support students), whilst in the second and third years it was integrated into more traditional workshop-style teaching sessions (led by a librarian). Following work described in Joint (2003), library staff now wish to assess the longer term impact on learning of both the courseware itself and the way the courseware is delivered to students. However, the existing evaluation data does not adequately support this type of assessment. Teaching sessions are routinely evaluated by means of simple feedback forms, with four questions answered using a five-point Likert scale, collected at the conclusion of each session. According to Fitzpatrick (1998), such feedback forms measure students' reactions and represent but the first level of evaluation. Learning, which can be defined as the extent to which a student changes attitudes, improves knowledge and/or increases skill as a result of exposure to the training, is the second level and is not being measured with these forms. A more comprehensive programme of evaluation, including logging usage of the courseware outside teaching sessions and follow-up of students several months after their introduction to the courseware, is now being established to support a more meaningful assessment of impact of the courseware on student learning

Universal dual amplitudes and asymptotic expansions for gg→Hgg\to H and H→γγH\to \gamma\gamma in four dimensions

Though the one-loop amplitudes of the Higgs boson to massless gauge bosons are finite because there is no direct interaction at tree-level in the Standard Model, a well-defined regularization scheme is still required for their correct evaluation. We reanalyze these amplitudes in the framework of the four-dimensional unsubtraction and the loop-tree duality (FDU/LTD), and show how a local renormalization solves potential regularization ambiguities. The Higgs boson interactions are also used to illustrate new additional advantages of this formalism. We show that LTD naturally leads to very compact integrand expressions in four space-time dimensions of the one-loop amplitude with virtual electroweak gauge bosons. They exhibit the same functional form as the amplitudes with top quarks and charged scalars, thus opening further possibilities for simplifications in higher-order computations. Another outstanding application is the straightforward implementation of asymptotic expansions by using dual amplitudes. One of the main benefits of the LTD representation is that it is supported in a Euclidean space. This characteristic feature naturally leads to simpler asymptotic expansions.Comment: 11 pages, no figures. Minor modifications, discussion improved. Final version published in EPJ

Two-loop QED corrections to the Altarelli-Parisi splitting functions

We compute the two-loop QED corrections to the Altarelli-Parisi (AP) splitting functions by using a deconstructive algorithmic Abelianization of the well-known NLO QCD corrections. We present explicit results for the full set of splitting kernels in a basis that includes the leptonic distribution functions that, starting from this order in the QED coupling, couple to the partonic densities. Finally, we perform a phenomenological analysis of the impact of these corrections in the splitting functions.Comment: 17 pages, 5 figures. Typos corrected, 1 figure added. Final version published in JHEP. Comment added about Eq. (51