Pseudoscalar correlators and the problem of the chiral limit in the compact lattice QED with Wilson fermions

The phase diagram for the compact lattice QED with Wilson fermions is shown. We discuss different methods for the calculation of the 'pion' mass $m_{\pi}$ near the chiral transition point $\kappa_c(\beta )$.Comment: 3 pages, TALK GIVEN AT THE LATTICE '94 INTERNATIONAL SYMPOSIUM LATTICE FIELD THEORY, BIELEFELD, GERMANY, SEPTEMBER 27 -- OCTOBER 1, 1994 Three figures are included as ps-files. Look for %%%%% FIG1.PS %%%% , et

Compact Lattice QED with Staggered Fermions and Chiral Symmetry Breaking

Different formulations of the $4d$ compact lattice QED with staggered fermions (standard Wilson and modified by suppression of lattice artifacts) are investigated by Monte Carlo simulations within the quenched approximation. We show that after suppressing lattice artifacts the system undergoes a phase transition from the Coulomb phase into a presumably weakly chirally broken phase only at (unphysical) negative $\beta$--values.Comment: 7 pages, 5 figures attached in compressed postscript files, preprint DESY-IfH and HU Berlin-IEP-94/11, submitted to Phys. Lett.

Efficiency of different matrix inversion methods applied to Wilson fermions

We compare different conjugate gradient -- like matrix inversion methods (CG, BiCGstab1 and BiCGstab2) employing for this purpose the compact lattice quantum electrodynamics (QED) with Wilson fermions. The main goals of this investigation are the CPU time efficiency of the methods as well as the influence of machine precision on the reliability of (physical) results especially close to the 'critical' line ~\kappa_c(\bt).Comment: 27 pages LaTeX (epsf), all figures include

Passing through the `chiral limit' in quenched QCD with Wilson fermions

We investigate the limit of vanishing quark mass in quenched lattice QCD with unimproved Wilson fermions at $\beta=6.0$. Exploiting the correlations of propagators at different time slices we extract pion masses extremely close to the `chiral limit', despite the presence of `exceptional configurations'. With this at hand, the existence of quenched chiral logarithms can be demonstrated, provided, finite size effects are small. With reference to the phase diagram proposed by Aoki also the range $\kappa > \kappa_c$ is investigated. The width of a potential parity-flavor violating phase can, if at all, hardly be resolved.Comment: LATTICE98(spectrum

Performance studies of the two-step multiboson algorithm in compact lattice QED

The performance of the two-step multiboson (TSMB) algorithm is investigated in comparison with the hybrid Monte Carlo (HMC) method for compact lattice QED with standard Wilson fermions both in the Coulomb and confinement phases. The restriction to QED allows for extensive measurements of autocorrelation times. Preliminary results show that the TSMB algorithm is at least competitive with standard HMC.Comment: Talk at Lattice2001(algorithms), Berlin, 3 pages, LaTe

Precision calculation of the pi^- deuteron scattering length and its impact on threshold pi-N scattering

We present a calculation of the pi^- d scattering length with an accuracy of a few percent using chiral perturbation theory. For the first time isospin-violating corrections are included consistently. Using data on pionic deuterium and pionic hydrogen atoms, we extract the isoscalar and isovector pion-nucleon scattering lengths and obtain a^+=(7.6 +/- 3.1) x 10^{-3} mpi^{-1} and a^-=(86.1 +/- 0.9) x 10^{-3} mpi^{-1}. Via the Goldberger-Miyazawa-Oehme sum rule, this leads to a charged-pion-nucleon coupling constant g_c^2/4 pi = 13.69 +/- 0.20.Comment: 6 pages, 2 figures. Discussion of several points expanded, references added in this version, which will appear in Physics Letters

Isospin breaking in the pion-nucleon scattering lengths

We analyze isospin breaking through quark mass differences and virtual photons in the pion-nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory (C) 2009 Elsevier B.V. All rights reserved

Coherent elastic neutrino-nucleus scattering: EFT analysis and nuclear responses

The cross section for coherent elastic neutrino-nucleus scattering (CEνNS) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a Z boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current CEνNS experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-vector part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of CEνNS on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In particular, we stress that in this case, even for vector and axial-vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for vector, axial-vector, but also (pseudo)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory (EFT). Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-vector responses