Multiplet bases, recursion relations and full color parton showers
Author
Summary, in English
Paper I concerns the decomposition of QCD color structures into multiplet bases, using Wigner 3j and 6j coefficients. A strong constraint is put on the required Wigner coefficients for leading order and next-to-leading order QCD amplitudes. The required Wigner coefficients for up to six external gluons were calculated by the method described in the
paper.
In paper II the results of paper I is applied to maximally helicity violating amplitude recursion relations, to investigate the viability of multiplet bases in this context. The result is a shift in the computational bottleneck of recursion, from the squaring of amplitudes to the recursion step, but yielding an overall better scaling for the total number of terms encountered.
In paper IV a more general method of constructing multiplet bases is presented, which improves the decomposition of paper I for amplitudes with quarks. New basis vectors are constructed by the presented method and from them Wigner 6j cofficients are calculated.
Paper III concerns the implementation of an Nc=3 parton shower in the event generator Herwig. In the implementation, the trace basis has been used, but it could, in a straight-forward way, be extended to other color space bases. The implementation has been used to study the effects of subleading color corrections, for both LEP and LHC events. The effects on observables are comparable to earlier findings for LEP, up to ~10% differences, compared to a leading color shower. For LHC the differences are often of the order of a few percent, but in some cases differences of up to 20% were found.
Publishing year
2018-09
Language
English
Full text
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Document type
Dissertation
Publisher
Lund University, Faculty of Science, Department of Astronomy and Theoretical Physics
Topic
- Subatomic Physics
Keywords
- QCD
- Multiplet Bases
- SU(Nc)
- SU(N)
- Recursion Relations
- BCFW
- Nc=3 Parton Showers
- Parton Showers
Status
Published
Supervisor
ISBN/ISSN/Other
- ISBN: 978-91-7753-855-4
- ISBN: 978-91-7753-854-7
Defence date
26 October 2018
Defence time
10:15
Defence place
Lundmarksalen, Astronomihuset, Sölvegatan 27, Lund
Opponent
- Davison E. Soper (Professor)