On strongly coupled quenched QED4, again: chiral symmetry breaking, Goldstone mechanism and the nature of the continuum limit

We explore the possibility of a trivial continuum limit of strongly coupled quenched QED4 by contrasting our results with a Nambu--Jona Lasinio equation of state. The data does not compare favorably with such scenario. We study in detail the interplay of chiral symmetry breaking with the Goldstone mechanism, and clarify some puzzling features of past results.Comment: Contribution to Lat94, 3 pages, tar-compressed uuencoded ps fil

Improving the Lattice QED Action

Strongly coupled QED is a model whose physics is dominated by short-ranged effects. In order to assess which features of numerical simulations of the chiral phase transition are universal and which are not, we have formulated a quenched version of the model in which photon degrees of freedom are defined on a lattice of spacing a, but fermions only on a lattice of spacing 2a. The fermi-photon interaction is then obtained via a blocking procedure, whose parameters allow a degree of control over the relative importance of short wavelength modes. Results from a variety of models are presented; the critical exponents delta and beta governing the transition appear to be independent of the blocking, or even of whether a gauge-invariant action is used for the photons.Comment: 3 pages LaTeX submission to Lat' 94 proceedings, 3 PostScript figures incorporated using macro psfi

Probing the Continuum Limit in Non-Compact QED: New Results on Large Lattices

We present new Monte Carlo results in non-compact lattice QED with staggered fermions down to m_0 = 0.005. This extends our previous investigations on the nature of the continuum limit of QED.Comment: 7 pages, uuencoded compressed PostScript, also available at ftp://ftp.zib-berlin.de/pub/zib-publications/Reports/SC-94-31.ps.

QED: Chiral transition and the issue of triviality

I give a review and progress report on studies of lattice QED. I emphasize analytical results and methods that are applied in data analysis. Also, I derive some bounds for the critical exponents and establish their connection with scaling violations. Triviality, as realized in $\phi^4$ theory, is ruled out on theoretical grounds. I show that the present data, if analyzed correctly, all lead to the same conclusions. They are compatible with power law scaling with nongaussian exponents.Comment: 6 pages, 7 figures (not included), ILL-(TH)-93-2

Magnetic Monopoles in non-compact QED - is there a Phase Transition?

The existence of the monopole condensation transition reported by Kocic et al. in non-compact, quenched QED is tested. No phase transition is found. This shows that divergence of the `monopole susceptibility' introduced by Hands and Wensley is not a reliable indicator of second order phase transitions. In view of these results I discuss claims that the chiral phase transition seen in QED with fermions is a lattice artefact driven by monopole condensation.Comment: Talk given at lattice '92, 4 pages, uses espcrc2.sty, 2 postscript figures attached. (Replaced to add the figures.) Preprint FUB-HEP 22/9

The present status of non-compact lattice QED

We give a 1993 update of non-compact lattice QED, in particular the chiral condensate, finite size effects and meson mass ratios. We compare descriptions of the phase transition. Our previous conclusions remain valid.Comment: Poster presentation at LAT93, Dallas, U.S.A. Postscript file, 4 pages, figures included. Preprint numbers DESY-93-178, FUB-HEP/93-20 and HLRZ 93-7

Compositeness, Triviality and Bounds on Critical Exponents for Fermions and Magnets

We argue that theories with fundamental fermions which undergo chiral symmetry breaking have several universal features which are qualitatively different than those of theories with fundamental scalars. Several bounds on the critical indices $\delta$ and $\eta$ follow. We observe that in four dimensions the logarithmic scaling violations enter into the Equation of State of scalar theories, such as $\lambda\phi^4$, and fermionic models, such as Nambu-Jona-Lasinio, in qualitatively different ways. These observations lead to useful approaches for analyzing lattice simulations of a wide class of model field theories. Our results imply that $\lambda\phi^4$ {\it cannot} be a good guide to understanding the possible triviality of spinor $QED$.Comment: 12 pages, 3 figures (not included), ILL-(TH)-93-2

Susceptibility to oxidative stress, insulin resistance, and insulin secretory response in the development of diabetes from obesity

Background/Aim. Oxidative stress plays a critical role in the pathogenesis of various diseases. Recent reports indicate that obesity may induce systemic oxidative stress. The aim of the study was to potentiate oxidative stress as a factor which may aggravate peripheral insulin sensitivity and insulinsecretory response in obesity in this way to potentiate development of diabetes. The aim of the study was also to establish whether insulin-secretory response after glucagonstimulated insulin secretion is susceptible to prooxidant/ antioxidant homeostasis status, as well as to determine the extent of these changes. Methods. A mathematical model of glucose/insulin interactions and C-peptide was used to indicate the degree of insulin resistance and to assess their possible relationship with altered antioxidant/prooxidant homeostasis. The study included 24 obese healthy and 16 obese newly diagnozed non-insulin dependent diabetic patients (NIDDM) as well as 20 control healthy subjects, matched in age. Results. Total plasma antioxidative capacity, erythrocyte and plasma reduced glutathione level were significantly decreased in obese diabetic patients, but also in obese healthy subjects, compared to the values in controls. The plasma lipid peroxidation products and protein carbonyl groups were significantly higher in obese diabetics, more than in obese healthy subjects, compared to the control healthy subjects. The increase of erythrocyte lipid peroxidation at basal state was shown to be more pronounced in obese daibetics, but the apparent difference was obtained in both the obese healthy subjects and obese diabetics, compared to the control values, after exposing of erythrocytes to oxidative stress induced by H2O2. Positive correlation was found between the malondialdehyde (MDA) level and index of insulin sensitivity (FIRI). Conclusion. Increased oxidative stress together with the decreased antioxidative defence seems to contribute to decreased insulin sensitivity and impaired insulin secretory response in obese diabetics, and may be hypothesized to favour the development of diabetes during obesity

Three-point functions in noncompact lattice QED

We calculate fermion-antifermion-"meson" three-point functions in noncompact lattice QED with dynamical staggered fermions and use them to extract effective Yukawa couplings. The results are consistent with the hypothesis that QED is trivial.Comment: Latex article. 3 pages, ps file. Contribution to LAT93, Dallas, U.S.A. HLRZ preprint 93-7

Universal Properties of Chiral Simmetry Breaking

We discuss chiral symmetry breaking critical points from the perspective of PCAC, correlation length scaling and the chiral equation of state. A scaling theory for the ratio $R_\pi$ of the pion to sigma masses is presented. The Goldstone character of the pion and properties of the longitudinal and transverse chiral susceptibilities determine the ratio $R_\pi$ which can be used to locate critical points and measure critical indices such as $\delta$. We show how PCAC and correlation length scaling determine the pion mass' dependence on the chiral condensate and lead to a practical method to measure the anomalous dimension $\eta$. These tools are proving useful in studies of the chiral transition in lattice QED and the quark-gluon plasma transition in lattice QCD.Comment: 19 pages, 4 figures. CERN-TH.6630/92 ILL-(TH)-92-1