Showing papers by "Manfried Faber published in 2008"

Center vortices and the Dirac spectrum

Abstract: Institute of Physics, Slovak Academy of Sciences, SK–845 11 Bratislava, Slovakia(Dated: June 20, 2008)We study correlations between center vortices and the low-lying eigenmodes of the Dirac operator, in boththe overlap and asqtad formulations. In particular we address a puzzle raised some years ago by Gattnar et al.[Nucl. Phys. B 716, 105 (2005)], who noted that the low-lyingDirac eigenmodes required for chiral symmetrybreaking do not appear to be present in center-projected configurations. We show that the low-lying modes are infact present in the staggered (asqtad) formulation, but not in the overlap and “chirally improved” formulations,and suggest a reason for this difference. We also confirm and e xtend the results of Kovalenko et al. [Phys.Lett. B 648, 383 (2007)], showing that there is a correlation between center vortex locations, and the scalardensity of low-lying Dirac eigenmodes derived from unprojected configurations. This correlation is strongestat points which are associated, in the vortex picture, with non-vanishing topological charge density, such asvortex intersection and “writhing” points. We present supp orting evidence that the lowest Dirac eigenmodes,in both asqtad and overlap formulations, have their largest concentrations in point-like regions, rather than onsubmanifolds of higher dimensionality.I. INTRODUCTION

Weak decays of H-like 140 Pr 58+ and He-like 140 Pr 57+ ions

Abstract: The nuclear K-shell electron-capture (EC) and positron ({beta}{sup +}) decay constants, {lambda}{sub EC} and {lambda}{sub {beta}{sup +}} of H-like {sup 140}Pr{sup 58+} and He-like {sup 140}Pr{sup 57+} ions, measured recently in the experimental storage ring (ESR) at GSI, were calculated using standard weak interaction theory. The calculated ratios R={lambda}{sub EC}/{lambda}{sub {beta}{sup +}} of the decay constants agree with the experimental values within an accuracy better than 3%.

Tests of the lattice index theorem

Abstract: We investigate the lattice index theorem and the localization of the zero modes for thick classical center vortices. For nonorientable spherical vortices, the index of the overlap Dirac operator differs from the topological charge although the traces of the plaquettes deviate only by a maximum of 1.5% from trivial plaquettes. This may be related to the fact that even in Landau gauge some links of these configuration are close to the nontrivial center elements.

Kinematics and Quantum Field Theory of the Neutrino Oscillations Observed in the Time-modulated Orbital Electron Capture Decay in an Ion Storage Ring

Abstract: According to the recent experimental data of a GSI--experiment, the rate of the number of daughter ions $^{140}{\rm Ce}^{58+}$, produced by a nuclear K--shell electron capture (EC) of the H--like ion ${^{140}}{\rm Pr}^{58+}$, is modulated in time with a period $T_d=(7.06\pm 8) $seconds. We explain this phenomenon by neutrino--flavour mixing and show that this can be understood within standard quantum field theory and derive a value for the squared mass difference $\Delta m^2_{21}=m^2_2-m^2_1=(0.763\pm 8) \cdot 10^{-4} \mathrm{eV}^2$. This proves that such processes provide a precise method to investigate neutrino--flavour mixing.

First-forbidden continuum- and bound-state beta--decay rates of bare Hg-205**80+ and Tl-207**81+ Ions

Abstract: We calculate the decay rates lambda_(beta^-_c) and lambda_(beta^-_b) of the continuum- and bound-state beta^- decays for bare 205Hg80+ and 207Tl81+ ions For the ratio of the decay rates R_(b/c) = lambda_(beta^-_b)/lambda_(beta^-_c) we obtain the values R_(b/c) = 0161 and R_(b/c) = 0190 for bare 205Hg80+ and 207Tl81+ ions, respectively The theoretical value of the ratio R_(b/c) = 0190 for the decays of 207Tl81+ agrees within 1% of accuracy with the experimental data R^exp_(b/c) = 0188(18), obtained at GSI The theoretical ratio R_(b/c) = 0161 for 205Hg80+ is about 20% smaller than the experimental value R^exp_(b/c) = 020(2), measured recently at GSI

Shape Vibrations of Topological Fermions

Abstract: We analyze the model of topological fermions, where charged fermions are treated as topological solitons We discuss vibrations of soliton shapes It is shown that depending on the power of the potential term (discrete parameter m) of the model Lagrangian the spectrum of normal mode frequencies can be discrete (for m = 1) or continuous (for m ≥ 2)

On strangeness production in the reactions pp → p 0 K + and pn → n 0 K + near threshold

Abstract: The cross sections for the reactions pp → p� 0 K + and pn → n� 0 K + are calculated near threshold of the final states. The theoretical ratio of the cross sections R = �(pn → n� 0 K + )/�(pp → p� 0 K + ) ≃ 3 shows the enhancement of the pn interaction with respect to the pp interaction near threshold of the strangeness production N� 0 K + . Such an enhancement is caused by the contribution of the np interaction in the isospin–singlet state, which is stronger than the pn interaction in the isospin–triplet state. For the confirmation of this result we calculate the cross sections for the reactions pp → pp� 0 , � 0 p → � 0 K + and � − p → � 0 K 0 near threshold of the final states. The theoretical cross sections agree well with the experimental data.

Can the "Darmstadt oscillations" be treated as two closely spaced mass-eigenstates of the H-like mother ions ?

Abstract: We discuss the proposal that the “Darmstadt oscillations” of the orbital K–shell electron capture decay (EC) rate of the H–like heavy ions are caused by quantum beats of two coherently excited, closely spaced mass–eigenstates of decaying H–like heavy ions. We show that such a mechanism to explain the time modulation of the EC–decay rates of the H–like heavy ions leads to the time modulation of the � + –decay rate of these ions with the same period. Such a time–dependence of the � + –decay rate of the H–like heavy ions contradicts the experimental data of GSI.

Center vortex influence on the Dirac spectrum

Abstract: We study the influence of center vortices on the low-lying eigenmodes of the Dirac operator, in both the overlap and asqtad formulations For center-projected configurations, one finds that the low-lying near-zero modes are present in the staggered (asqtad) formulation, but not in the overlap and "chirally-improved" formulations We argue that this is due to the absence of a field-independent chiral symmetry in the latter formulations, when the Dirac operator is evaluated on the very rough configurations generated by center projection We also confirm and extend the results of Kovalenko et al [Phys Lett B 648, 383 (2007)], finding strong correlations between center vortex locations, and the scalar density of low-lying Dirac eigenmodes on unprojected lattices, in both asqtad and overlap formulations It is found that the low-lying eigenmodes have their largest concentrations in point-like regions, rather than on submanifolds of higher dimensionality