1,721,006 research outputs found
QCD Meets Gravity 2023
No full textTwist-2 operators play an important role in QCD: they arise from the operator product expansion in deep-inelastic scattering and underlie the definition of collinear parton distribution functions (PDFs). We discuss the calculation of heavy quark contributions to matrix elements of these twist-2 operators at three-loop order in QCD. These matrix elements serve as matching coefficients to connect PDFs with different number of active quark flavours and enter the description of heavy quark contributions to deep-inelastic scattering. Different aspects of the problem are most suitably treated in three different mathematical spaces. They are connected by Mellin transformations and generating functions. We highlight interesting connections between these spaces, in particular how to compute the inverse Mellin transformation using generating functions and analytic continuation. These connections generalise also beyond the context of twist-2 operators in QCD
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Three-loop QCD corrections from massive quarks to deep-inelastic structure functions and operator matrix elements
Get PDFThis thesis discusses higher-order contributions from heavy quarks to inclusive
deep-inelastic lepton-nucleon scattering. In this context, massive operator
matrix elements play an important role: they enter into the heavy flavour Wilson
coefficients through a factorisation relation in the asymptotic limit of large
virtualities. Furthermore, they also enter into the definition of the variable
flavour number scheme for parton distributions.
Here, we present the analytic calculation of of several such massive operator
matrix elements at the 3-loop level in perturbative quantum chromodynamics. In
particular, we review the necessary mathematical and computational methods for
these calculations and give results for the non-singlet and pure-singlet
operator matrix elements including their applications in the structure
functions, sum rules and and the variable flavour number scheme. Through this
calculation we also obtain the pure-singlet and non-singlet anomalous dimensions
at 3-loop order. Moreover, we discuss the calculation of certain representative
Feynman diagrams with ladder and V-topologies, which serve as a testing ground
for the calculational tools. Finally, also all Feynman diagrams of the gluonic
operator matrix element are calculated, which is required in a 3-loop
description of the variable flavour number scheme
- …
