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Decays of η to three pions
Povišer, Martin ; Zdráhal, Martin (advisor) ; Kolesár, Marián (referee)
In this work, we summarize a method established in the published literature of dispersive construc- tion of amplitude for the ! decay process. We outline Chiral Perturbation Theory (ChPT) as an effective field theory for the description of low-energy hadron dynamics, and then introduce dispersive methods with the objective of constructing process amplitudes (up to the two-loop order) similar in form to ChPT predictions. The original contribution of the present work is a software library implementing the reconstruction procedure that forms the basis for the dispersive construction of mesonic process amplitudes. This library can be used to construct amplitudes in a computer algebra system (CAS) environment, making those forms of amplitude available to fitting of experimental data and theoretical studies, especially those focusing on the extraction of the up/down quark mass difference. 1
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Nová fyzika v procesech při nízkých energiích
Husek, Tomáš ; Kampf, Karol (advisor) ; Kolesár, Marián (referee)
Not so long ago, the value of the branching ratio of a neutral pion decay to an electron-positron pair (π0 → e− e+ ) has been updated and became more accurate thanks to the fact, that new measurements were performed at KTeV experiment at Fermilab. In this context it has been showed, that the Standard Model theoretical prediction is not precise enough. The resulting discrepancy was not explained yet. In presented work, there are summarized preceding results, al- ready computed correction were taken into account and newly the Bremsstrahlung contribution was thoroughly calculated. Besides, the contribution of π-loop cor- rections in terms of double-logarithms is estimated. In the end, because of the persisting disagreement of the accepted theory with the experiment, an additional contribution is suggested from beyond the Standard Model on the basis of models describing the dark matter. The latter mentioned is a hot candidate to explain many phenomena, for example the mysterious source of a great amount of γ-rays coming from the center of our galaxy and having the origin in the annihilation of electron-positron pairs. 1
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Order parameters of three-flavour chiral symmetry from ππ scattering
Říha, Jaroslav ; Kolesár, Marián (advisor) ; Kampf, Karol (referee)
This thesis familiarizes the reader with the process behind the construction of ππ scattering amplitudes. Several representations and transformations nec- essary to pass from one to another are introduced. Then known solutions of Roy equations are employed to extract values of subthreshold parameters αππ and βππ from recent experimental data. As a second goal three-flavour chiral perturbation theory(χPT), which is a low energy effective field theory of quan- tum chromodynamics, is used to obtain theoretical predictions for αππ and βππ by applying a technique called resummed approach. A large statistical ensemble of predictions is numerically generated. Subsequently, Bayesian statistics is uti- lized to get more information about spontaneous symmetry breaking parameters X(3), Y (3), Z(3), which are related to the leading order low energy coupling constants of three-flavour χPT. These results are then compared to several other recent determinations. Significant shifts in probability distributions compared to Descotes-Genon et al. [2004] are observed. The new results are more consistent with theoretical expectations. 1 Bibliography S. Descotes-Genon, N. H. Fuchs, L. Girlanda, and J. Stern. Resumming qcd vac- uum fluctuations in three-flavor chiral perturbation theory. The European Phys- ical Journal C,...
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Two-loop chiral corrections to the neutral pion decay to electron-positron pair
Farkaš, Kristián ; Novotný, Jiří (advisor) ; Kolesár, Marián (referee)
This thesis is devoted to the rare decay π0 → e+ e− . We firstly introduce all theoretical knowledge necessary for the description of the vertices used in this work. Subsequently, we introduce three two-loop chiral Feynman diagrams, which are of order O(α2 p4 ). These diagrams are firstly decomposed to Master integrals by Laporta algorithm. After that, we calculate each Master integral individually by the differential equation technique. We also focus on the renormalization of the process. Since we are working with the effective field theory, finite corrections χ from counterterm diagrams naturally appear. With use of the calculations listed in this thesis, the determination of the parameter χR could be further improved taking into account the whole two-loop correction. 1
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Studium řídkých procesů na experimentu NA62 v CERN
Kandra, Jakub ; Kampf, Karol (advisor) ; Kolesár, Marián (referee)
The primary objective is study of neutral pion decay into the Dalitz pair and photon. The thesis has two important parts, theoretical and experimental. The task of theoretical part is the analysis of studied decay mode with prediction of branching ratio of this decay. The next part should prove the theoretical prediction. The proof was done at real data at run 2007 of the experiment NA62 in European organization for nuclear research. The another task of this thesis is shown the modern methods of theoretical analysis and experimental measurement branching ratio. Powered by TCPDF (www.tcpdf.org)
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Nová fyzika v procesech při nízkých energiích
Husek, Tomáš ; Kampf, Karol (advisor) ; Kolesár, Marián (referee)
Not so long ago, the value of the branching ratio of a neutral pion decay to an electron-positron pair (π0 → e− e+ ) has been updated and became more accurate thanks to the fact, that new measurements were performed at KTeV experiment at Fermilab. In this context it has been showed, that the Standard Model theoretical prediction is not precise enough. The resulting discrepancy was not explained yet. In presented work, there are summarized preceding results, al- ready computed correction were taken into account and newly the Bremsstrahlung contribution was thoroughly calculated. Besides, the contribution of π-loop cor- rections in terms of double-logarithms is estimated. In the end, because of the persisting disagreement of the accepted theory with the experiment, an additional contribution is suggested from beyond the Standard Model on the basis of models describing the dark matter. The latter mentioned is a hot candidate to explain many phenomena, for example the mysterious source of a great amount of γ-rays coming from the center of our galaxy and having the origin in the annihilation of electron-positron pairs. 1
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Elektroslabé procesy v rámci efektivní polní teorie
Soukup, Petr ; Kampf, Karol (advisor) ; Kolesár, Marián (referee)
Title: Electroweak processes in the framework of effective field theory Author: Petr Soukup Department: Institute of Particle and Nuclear Physics Supervisor: RNDr. Karol Kampf, Ph.D. Supervisor's e-mail address: kampf@troja.mff.cuni.cz Abstract: In this thesis, we study electroweak processes within the framework of ef- fective field theory employing the approach of effective Lagrangians. We mainly focus on the decay process H → γγ. A complete set of SU(2) × U(1) invariant dimension- six operators is utilized. We present a brief introduction to GWS Standard model and dimension-six effective operators. One-loop Standard model contribution to the process of H → γγ is then evaluated, followed by calculation of tree-level and one-loop level dimension-six operators contribution to the same process. We then present a brief ge- neral summary of renormalization procedure in quantum field theory. Renormalization of performed calculations is implemented, and possible issues that may arise during renormalization of such non-renormalizable theory are also discussed. In the end, we discuss the obtained results, mainly the dependence of H → γγ decay rate on effective theory's free parameters and the scale of the new physics Λ. Focus is made on possible deviations from Standard model results. The results are plotted in charts....
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