Browsing by Author "Schilcher, Karl"

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    Hadronic matter: from vacuum to extreme temperature in the presence of magnetic fields
    (2016) Hernandez, Luis Alberto; Dominguez, Cesareo A; Weigert, Heribert; Schilcher, Karl
    This work consists of two themes. First, we work with Finite Energy QCD Sum Rules (FESR) approach in the vacuum. We tackle the problem of quark-hadron duality violation (DV), using the vector and axial-vector hadronic spectral function from tau-decay. A pinched integration kernel is introduce in the FESR in order to quench potential duality violations on the real axis in the complex squared energy plane and effectively extend the analysis well beyond the kinematical Ƭ-decay end-point. As the sum rules are well satisfied, we conclude that possible DV must be buried under the experimental uncertainties. Also, using the latest updated ALEPH data on hadron decays, we use FESR to determine the vacuum condensates of dimension d = 2 and d = 4, to check the validity of the Weinberg sum rules, and to determine the chiral condensates of dimension d = 6 and d = 8, and values of the chiral perturbation theory L10 and C87.
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    A quantum field theory for the interaction of pions and rhos
    (2017) Moodley, Preshin; Dominguez, Cesareo A; Schilcher, Karl; Tupper, Gary; Spiesberger, Hubert
    We extend the Kroll-Lee-Zumino model in its particle content to include the charged rho vector mesons and the neutral pion meson. This entailed using the larger SU(2) gauge group. The masses for the vector mesons were generated via spontaneous symmetry breaking using the Higgs mechanism. The Lagrangian was then quantized and gauge fixed using the generalized class of Rɛ gauges. Tree scattering lengths were calculated for pion-pion scattering and the values for the a₀⁰ and a₀² scattering lengths are found to be comparable with experiment. The one particle irreducible diagrams that contribute to the one loop corrections to the tree scattering lengths are renormalized.
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    Rho-Meson propagator at two-loop order in the Kroll-Lee-Zumino quantum field theory
    (2017) Lushozi, Mawande; Dominguez, Cesareo A; Schilcher, Karl
    The Kroll-Lee-Zumino theory, an Abelian renormalizable quantum field theory of charged pions and a neutral ρ meson, provides a framework to compute corrections to the tree-level Vector-Meson-Dominance model. Despite a large ρππ coupling (gρππ ≈ 5), the loop suppresion factor of 1=(4π)² helps give reasonably small NLO (one-loop) corrections. When it comes to describing hadronic physics, one might say, these one-loop results achieve moderate to excellent success. Where the one-loop results show less than impressive agreement with experiment, it seems plausible that the NNLO (two-loop) corrections would remedy the situation. In this thesis the two-loop contribution to the ρ⁰ meson is calculated. It turns out to be larger than the one-loop result and so one must conclude that perturbation theory breaks down at this level.