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

Phase structure and chiral limit of compact lattice QED with Wilson fermions

We study the phase structure and chiral limit of $4d$ compact lattice QED with Wilson fermions (both dynamical and quenched). We use the standard Wilson action (WA) and also the modified action (MA) with some lattice artifacts suppressed. We show that lattice artifacts influence the distributions of eigenvalues $~\lambda_i~$ of the fermionic matrix especially for small values of $~\lambda_i~$. Our main conclusion is that the chiral limit of compact QED can be efficiently located using different techniques. Sorry, figures are not included and can be sent by ordinary mail or Fax.Comment: TALK GIVEN AT THE LATTICE '93 INTERNATIONAL SYMPOSIUM LATTICE FIELD THEORY, DALLAS, USA, OCTOBER 12--16, 1993 3 page

Zero-momentum modes and chiral limit in compact lattice QED

The influence of zero-momentum gauge modes on physical observables is investigated for compact lattice QED with dynamical and quenched Wilson fermions. Within the Coulomb phase, zero-momentum modes are shown to hide the critical behaviour of gauge invariant fermion observables near the chiral limit. Methods for eliminating zero-momentum modes are discussed.Comment: Talk at Lattice 2000, Bangalore, 4 pages, 3 figures, LaTe

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.

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

Dirac sheets and gauge fixing in U(1)U(1) lattice gauge theory

Photon correlators in $~U(1)~$ pure gauge theory for different lattice actions are considered under the Lorentz gauge condition. They are shown to depend strongly on the gauge fixing ambiguity and on the corresponding existence of Dirac sheets. For the Coulomb phase a gauge fixing algorithm is proposed which avoids Dirac sheets and allows to find the global extremum of the non-local gauge condition. Sorry, figures are not included and can be sent by ordinary mail.Comment: 11 pages preprint HU Berlin--IEP--93/2, June 199

Hadron masses in qQCD with Wilson fermions near the chiral limit

In quenched lattice QCD with standard Wilson fermions the quark propagator is computed very close to the chiral limit in the zero-temperature case. Starting from our experience with lattice QED we employ a modified statistical method in order to estimate reliably hadron masses.Comment: 8 (single column-) pages, contribution to LATTICE 9

On the stability of Dirac sheet configurations

Using cooling for SU(2) lattice configurations, purely Abelian constant magnetic field configurations were left over after the annihilation of constituents that formed metastable Q=0 configurations. These so-called Dirac sheet configurations were found to be stable if emerging from the confined phase, close to the deconfinement phase transition, provided their Polyakov loop was sufficiently non-trivial. Here we show how this is related to the notion of marginal stability of the appropriate constant magnetic field configurations. We find a perfect agreement between the analytic prediction for the dependence of stability on the value of the Polyakov loop (the holonomy) in a finite volume and the numerical results studied on a finite lattice in the context of the Dirac sheet configurations

Frequency dependence of magnetothermal properties for magnetic fluid and magnetically functionalized implants

Heating of the magnetic nanoparticles in AC magnetic field is the effect promising for application in medicine. The mechanisms of heating in AC-magnetic field implies nontrivial dependence of the power dissipated by magnetic nanoparticles on frequency. With the use of a reconfigurable experimental setup, this frequency-dependent magnetic heating was measured on two characteristic examples: the magnetite nanoparticles conventionally used in medicine and polymer coating with micrometer sized magnetite particles. The saturation of the heating power with frequency is shown that is more pronounced for the second case of microparticles