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In this thesis a method for decomposing QCD colour structures into multiplet bases is described. The method is applicable for any number of gluons and quarks. To achieve the decomposition requires the knowledge of group theoretical weights, so-called Wigner 3j and 6j coefficients. The number of required coefficients have been calculated for up to 12 external gluons, and been shown to scale well in
Top quark pairs production and decay are considered in the framework of the smeared-mass unstable particles model. The results are in good agreement with the previous ones in the literature. Suggested approach significantly simplifies calculations compared to the standard perturbative one.
We calculate cross-section of the near-threshold three-boson production at the ILC with an account of their instability and a principal part of NLO corrections. The calculations are fulfilled within the framework of the model of unstable particles with smeared mass. We show that the contribution of finite width (instability) is large in the resonance Higgs-mass range and should be taken into accou
Over the years, many jet clustering algorithms have been proposed for the analysis of hadronic final states in e+e- annihilations. These have somewhat different emphasis and are therefore more or less suited for various applications. We here review some of the most used and compare them from a theoretical and experimental point of view.
I present higher loop order results for several calculations in Chiral perturbation Theory. 1) Two-loop results at finite volume for hadronic vacuum polarization. 2) A three-loop calculation of the pion mass and decay constant in two-flavour ChPT. For the pion mass all needed auxiliary parameters can be determined from lattice calculations of ππ-scattering. 3) Chiral corrections to neutron-anti-ne
This talk is about the hadronic light-by-light contribution to the muon anomalous magnetic moment, mainly our old work but including some newer results as well. It concentrates on the model calculations. Most attention is paid to pseudo-scalar exchange and the pion loop contribution. Scalar, a1-exchange and other contributions are shortly discussed as well. For the π0-exchange a possible large can
A semiclassical model is presented for the way the energy of a fast quark is transformed into observable hadrons. It reproduces the features of 1 + 1 dimensional QED (the Schwinger model) concerning a flat rapidity distribution in the central region. In particular the model predicts that the probability to find a meson containing a leading quark is independent of the Feynman scaling variable. Also
The ideas presented in an earlier note on the relationship between the quark fragmentation distributions as measured in leptoproduction and the one particle distributions in the mesonic fragmentation regions of hadronic interactions are carried further to photoproduction and to the baryon fragmentation distributions. The results are as before interpreted in terms of a simple additive quark model w
The renormalization of chiral perturbation theory is carried out to next-to-next-to-leading order in the meson sector. We calculate the divergent part of the generating functional of Green functions of quark currents to O(p6) for chiral SU(n), involving one- and two-loop diagrams. The renormalization group equations for the renormalized low-energy constants of O(p6) are derived. We compare our res
In this work, we consider expressions for the masses and decay constants of the pseudoscalar mesons in SU(3) chiral perturbation theory. These involve sunset diagrams and their derivatives evaluated at p2=mP2 (P=π, K, η). Recalling that there are three mass scales in this theory, mπ, mK and mη, there are instances when the finite part of the sunset diagrams do not admit an expression in terms of e
We present our studies of four-jet double parton scattering production in proton-nucleus collisions within the framework of the pythia8 event generator. We demonstrate that double absorptive processes in pA generated by the Angantyr model in pythia8 give an enhancement of the total double parton scattering cross section similar to the predictions by Strikman and Treleani in 2001. Additionally, we
Some of the shortcomings of the Standard Model of particle physics are the 'unnatural' value of the mass of the Higgs boson and the fact that the model cannot account for the process of baryogenesis - a mechanism which generates the observed asymmetry between matter and anti-matter in the Universe. The former is related to the fundamental scalar nature of the Higgs boson, connected to quad
In this thesis, a holographic model for quantum chromodynamics (QCD) is used to estimate the electromagnetic contribution to the kaon mass difference. The principal ideas of the model are inspired by the AdS/CFT correspondence, which is believed to be exact. The calculation is first performed theoretically, highlighting the expansion of the result into a diagrammatic structure referred to as Witte
