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When scale symmetry is combined with chiral symmetry in a scale-chiral Lagrangian, it can be shown in Fermi-liquid fixed point theory that $g_A^{\rm eff}\approx 1$ in finite nuclei {\it as well as} in dense baryonic matter. This is suggested as a signal for emergence of hidden symmetries of QCD in baryonic matter from low to very high density. This calculation throws doubt on the "first principles" explanation of the quenching of $g_A$ in nuclei with two-body meson-exchange currents. It also has relevance to Gamow-Teller matrix elements in neutrinoless double $\beta$ decay., Comment: 9 pages, 2 figures; this version gives a firmer conclusion

By incorporating hidden scale symmetry and hidden local symmetry in nuclear effective field theory, combined with double soft-pion theorem, we predict that the Gamow-Teller operator coming from the space component of the axial current should remain unaffected by the QCD vacuum change caused by baryonic density whereas the first forbidden beta transition operator coming from the time component should be strongly enhanced. While the latter has been confirmed since some time, the former is given a support by a powerful recent {\it ab initio} quantum Monte Carlo calculation in light nuclei, also confirming the old "chiral filter hypothesis." Formulated in terms of Fermi-liquid fixed point structure of strong-coupled nuclear interactions, we offer an extremely simple resolution to the long-standing puzzle of "quenched $g_A$", $g_A^{\rm eff}\approx 1$~\cite{quenched}, in nuclear Gamow-Teller beta transitions, giant Gamow-Teller resonances and double beta decays., More discussions are added. Several typos are corrected

We present an analytic representation of $F_K/F_\pi$ as calculated in three-flavour two-loop chiral perturbation theory, which involves expressing three mass scale sunsets in terms of Kamp\'e de F\'eriet series. We demonstrate how approximations may be made to obtain relatively compact analytic representations. An illustrative set of fits using lattice data is also presented, which shows good agreement with existing fits., Comment: v.2, version accepted for publication in Physical Review D as Rapid Communication; 8 pages, 5 figures; figure 1 replaced, full results for sunsets included, updated lattice fitting section, references added, clarifications introduced

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 $p^2=m_P^2$ ($P=\pi, K, \eta$). Recalling that there are three mass scales in this theory, $m_\pi$, $m_K$ and $m_\eta$, there are instances when the finite part of the sunset diagrams do not admit an expression in terms of elementary functions, and have therefore been evaluated numerically in the past. In a recent publication, an expansion in the external momentum was performed to obtain approximate analytic expressions for $m_\pi$ and $F_\pi$, the pion mass and decay constant. We provide fully analytic exact expressions for $m_K$ and $m_\eta$, the kaon and eta masses, and $F_K$ and $F_\eta$, the kaon and eta decay constants. These expressions, calculated using Mellin-Barnes methods, are in the form of double series in terms of two mass ratios. A numerical analysis of the results to evaluate the relative size of contributions coming from loops, chiral logarithms as well as phenomenological low-energy constants is presented. We also present a set of approximate analytic expressions for $m_K$, $F_K$, $m_\eta$ and $F_\eta$ that facilitate comparisons with lattice results. Finally, we show how exact analytic expressions for $m_\pi$ and $F_\pi$ may be obtained, the latter having been used in conjunction with the results for $F_K$ to produce a recently published analytic representation of $F_K/F_\pi$., Comment: 50 pages, 4 figures; ancillary Mathematica file

Universität Hamburg, Diss., 2005; 125 pp., (2005). doi:10.3204/DESY-THESIS-2005-023, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Universität Hamburg, Diss., 2002; 121 pp., (2002). doi:10.3204/DESY-THESIS-2002-044, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Physical review / D 57(9), 5562 - 5580 (1998). doi:10.1103/PhysRevD.57.5562, We compute the hadron mass spectrum, the quark masses and the meson decay constants in quenched lattice QCD with non-perturbatively $O(a)$ improved Wilson fermions. The calculations are done for two values of the coupling constant, $\beta = 6.0$ and 6.2, and the results are compared with the predictions of ordinary Wilson fermions. We find that the improved action reduces lattice artifacts as expected., Published by Inst., Woodbury, NY