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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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Studium rezonancí v anomálním sektoru kvantové chromodynamiky
Kadavý, Tomáš ; Kampf, Karol (advisor) ; Trnka, Jaroslav (referee)
The independent operator basis of the most important resonances in the so-called odd-intrinsic parity sector was formulated in [1]. Using these ope- rators we can construct Lagrangians of corresponding Feynman diagrams, that allow us to describe and understand several interaction processes. In the mentioned article were studied Green functions for V V P and V AS correlators including their phenomenological aspects. This thesis should establish the Feynman rules for not so much known Green functions corresponding to AAP , V V A and AAA correlators. Because not enough theoretical or experimental attention has been paid to these correlators, we will not be able to perform phenomenological study. But we can return to this point in the future during master degree studies. Reference [1] K. Kampf and J. Novotny, Phys. Rev. D 84 (2011) 014036 [ar- Xiv:1104.3137 [hep-ph]]. 1
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Some aspects of low-energy QCD at the precision frontier
Husek, Tomáš ; Kampf, Karol (advisor) ; Hořejší, Jiří (referee) ; Passemar, Emilie (referee)
Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1
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Green functions of currents in the odd-intrinsic parity sector of QCD
Kadavý, Tomáš ; Kampf, Karol (advisor) ; Trnka, Jaroslav (referee)
Green functions of currents allow us to study resonances in the low- energy limit of QCD. Using them, we can construct amplitudes or decay widths of processes. By a comparison of the theoretical predictions with experimental measurements we can determine the values of parameters of the theory and obtain a more comprehensive understanding about the be- haviour of QCD processes. In our investigated topic, an odd-parity sector of QCD, exist five nontriv- ial three-point Green functions, also referred to as correlators. Correlators V V P and V AS have already been studied in [1], whilst a calculation of AAP was provided in [2]. In this thesis we therefore deal with the Green functions V V A and AAA that have not yet been studied before. We present a complete calculation of the contributing Feynman diagrams in the anti- symmetric tensor formalism that satisfies high-energy behaviour within the OPE framework, as was shown also in [2]. The obtained results are submit- ted to phenomenological studies. Further, we also present an introduction to our calculations of the four- point Green functions V V PP and V V V V . The calculations were carried out both in the antisymmetric tensor and vector formalism but due to the complicated tensor structure of the results, the calculations can not be shown here in their...
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Construction of pseudoscalar meson amplitudes in chiral perturbation theory using a dispersive approach
Zdráhal, Martin ; Novotný, Jiří (advisor) ; Bijnens, Johan (referee) ; Ecker, Gerhard (referee)
Title: Construction of pseudoscalar meson amplitudes in chiral perturbation theory using a dispersive approach Author: Martin Zdráhal Department: Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University in Prague Supervisor: RNDr. Jiří Novotný, CSc. Abstract: We have developed a method enabling a construction of two-loop 2 → 2 scatter- ing amplitudes of pseudoscalar mesons based on the dispersion and the unitarity relations. This method is illustrated on the construction of the amplitudes of all such processes in chiral perturbation theory in isospin limit taking into account strong interactions only. Then it was used for the construction of ππ scattering amplitudes and of K → 3π and η → 3π decay amplitudes including isospin breaking effects induced by different masses of the particles belonging to the same isomultiplet. These parametrizations are prepared for various phenomenological analyses of the ππ scattering lengths and of the isospin breaking effects, both of which could pro- vide us important information for the understanding of quantum chromody- namics at low energies. Finally, we have performed the phenomenological study of η → 3π decay and obtained a value of the quark mass ratio 1/R = (md − mu)/(ms − ˆm). Our conservative estimate is R = 39.6+2.5 −5.1....
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Some aspects of low-energy QCD at the precision frontier
Husek, Tomáš ; Kampf, Karol (advisor)
Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1
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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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Some aspects of low-energy QCD at the precision frontier
Husek, Tomáš ; Kampf, Karol (advisor)
Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1
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Some aspects of low-energy QCD at the precision frontier
Husek, Tomáš ; Kampf, Karol (advisor) ; Hořejší, Jiří (referee) ; Passemar, Emilie (referee)
Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1
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