|
|
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
|
|
|
Aspects of renormalization of spontaneously broken gauge theories
Hudec, Matěj ; Malinský, Michal (advisor) ; Beneš, Petr (referee)
In this thesis, we use the Coleman-Weinberg effective potential for computing the radiative corrections to scalar masses in six simple models of the quantum field theory. We probe, for example, the theory of two scalar fields, simple generalizations of the Abelian Higgs model or some classic extensions of the Standard Model. A common feature of all the theories considered is the existence of (at least) two mass scales different in order of magnitude. Being motivated by the hierarchy problem, we study mainly the sensitivity of light scalar masses on the radiative corrections induced by the heavy fields in relevant Feynman loops. We demonstrate that while the masses of scalars with zero VEV obtain corrections proportional to the masses of the heavy fields, in theories with the spontaneous symmetry breakdown is the Higgs mass always governed by the corresponding ordering parameter, i.e., by its vacuum expectation value. For the Standard Model, understood as an effective field theory, this implies that the Higgs boson mass is as stable with respect to the effects of possible new physics on very high energies as the masses of the leptons, quarks, W and Z bosons. Powered by TCPDF (www.tcpdf.org)
|
|
|
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....
|
guest ::
