Interplay of universality classes in a three-dimensional Yukawa model

We investigate numerically on the lattice the interplay of universality classes of the three-dimensional Yukawa model with U(1) chiral symmetry, using the Binder method of finite size scaling. At zero Yukawa coupling the scaling related to the magnetic Wilson--Fisher fixed point is confirmed. At sufficiently strong Yukawa coupling the dominance of the chiral fixed point associated with the 3D Gross--Neveu model is observed for various values of the coupling parameters, including infinite scalar selfcoupling. In both cases the Binder method works consistently in a broad range of lattice sizes. However, when the Yukawa coupling is decreased the finite size behavior gets complicated and the Binder method gives inconsistent results for different lattice sizes. This signals a cross-over between the universality classes of the two fixed points.Comment: 24 pp. LaTeX 2e src, needs psfig.st

Strongly coupled lattice gauge theory with dynamical fermion mass generation in three dimensions

We investigate the critical behaviour of a three-dimensional lattice \chiU\phi_3 model in the chiral limit. The model consists of a staggered fermion field, a U(1) gauge field (with coupling parameter $\beta$) and a complex scalar field (with hopping parameter $\kappa$). Two different methods are used: 1) fits of the chiral condensate and the mass of the neutral unconfined composite fermion to an equation of state and 2) finite size scaling investigations of the Lee-Yang zeros of the partition function in the complex fermion mass plane. For strong gauge coupling ($\beta < 1$) the critical exponents for the chiral phase transition are determined. We find strong indications that the chiral phase transition is in one universality class in this $\beta$ interval: that of the three-dimensional Gross-Neveu model with two fermions. Thus the continuum limit of the \chiU\phi_3 model defines here a nonperturbatively renormalizable gauge theory with dynamical mass generation. At weak gauge coupling and small $\kappa$, we explore a region in which the mass in the neutral fermion channel is large but the chiral condensate on finite lattices very small. If it does not vanish in the infinite volume limit, then a continuum limit with massive unconfined fermion might be possible in this region, too.Comment: 27 pages, 16 figure

Study of the Asymptotic Freedom of 2D Yukawa Models on the Lattice

We investigate on the lattice the Yukawa models in 2 dimensions with Z(2) and U(1) symmetries. These models reduce to the usual and chiral Gross-Neveu models, respectively, when the kinetic and the selfcoupling terms of the scalar field are turned off. The numerical data and mean field arguments suggest that, at least for some range of the scalar field hopping parameter, fermion mass is dynamically generated for arbitrarily weak Yukawa coupling. The models are asymptotically free in this coupling, like the Gross-Neveu models, even when the scalar quartic selfcoupling is strong.Comment: LaTeX, 11 pages (including 4 postscript figures); OUTP-93-01P (HLRZ 93-15

Magnetic and chiral universality classes in a 3D Yukawa model

The 3D Yukawa model with U(1) chiral symmetry is investigated in a broad interval of parameters using the Binder method. Critical exponents of the Wilson-Fisher (magnetic) and Gross-Neveu (chiral) universality classes are measured. The model is dominated by the chiral universality class. However at weak coupling we observe a crossover between both classes, manifested by difficulties with the Binder method which otherwise works well.Comment: 4 pages, contribution to LATTICE 9

On the equivalence between 2D Yukawa and Gross-Neveu models

We study numerically on the lattice the 2D Yukawa model with the U(1) chiral symmetry and $N_F$ = 16 at infinite scalar field self-coupling. The scaling behaviour of the fermion mass, as the Yukawa coupling approaches zero, is analysed using the mean field method. It is found to agree with that of the Gross-Neveu model with the same symmetry and $N_F$. The results suggest that the 2D Yukawa models belong to the universality class of the Gross-Neveu models not only at weak scalar field self-coupling but also for a broad range of the bare parameters which is not accessible to the $1/N_F$ expansion. New universality classes might arise at the crossover to the spin model universality class, however.Comment: 18 pages, Juelich HLRZ 111/9

Prospective External Validation of the Clinical Effectiveness of an Emergency Department-Based Early Goal-Directed Therapy Protocol for Severe Sepsis and Septic Shock

Objective: To determine the clinical effectiveness of implementing early goal-directed therapy (EGDT) as a routine protocol in the emergency department (ED). Methods: Prospective interventional study conducted over 2 years at an urban ED. Inclusion criteria included suspected infection, criteria for systemic inflammation, and either systolic BP < 90 mm Hg after a fluid bolus or lactate concentration ≥ 4 mol/L. Exclusion criteria were age < 18 years, contraindication to a chest central venous catheter, and need for immediate surgery. We prospectively recorded preintervention clinical and mortality data on consecutive, eligible patients for 1 year when treatment was at the discretion of board-certified emergency physicians. We then implemented an EGDT protocol (the intervention) and recorded clinical data and mortality rates for 1 year. Prior to the first year, we defined a 33% relative reduction in mortality (relative mortality reduction that was found in the original EGDT trial) to indicate clinical effectiveness of the intervention. Results: We enrolled 79 patients in the preintervention year and 77 patients in the postintervention year. Compared with the preintervention year, patients in the postintervention year received significantly greater crystalloid volume (2.54 L vs 4.66 L, p < 0.001) and frequency of vasopressor infusion (34% vs 69%, p < 0.001) during the initial resuscitation. In-hospital mortality was 21 of 79 patients (27%) before intervention, compared with 14 of 77 patients (18%) after intervention (absolute difference, − 9%; 95% confidence interval, + 5 to − 21%). Conclusions: Implementation of EGDT in our ED was associated with a 9% absolute (33% relative) mortality reduction. Our data provide external validation of the clinical effectiveness of EGDT to treat sepsis and septic shock in the ED

Two-dimensional model of dynamical fermion mass generation in strongly coupled gauge theories

We generalize the $N_F=2$ Schwinger model on the lattice by adding a charged scalar field. In this so-called $\chi U\phi_2$ model the scalar field shields the fermion charge, and a neutral fermion, acquiring mass dynamically, is present in the spectrum. We study numerically the mass of this fermion at various large fixed values of the gauge coupling by varying the effective four-fermion coupling, and find an indication that its scaling behavior is the same as that of the fermion mass in the chiral Gross-Neveu model. This suggests that the $\chi U\phi_2$ model is in the same universality class as the Gross-Neveu model, and thus renormalizable and asymptotic free at arbitrary strong gauge coupling.Comment: 18 pages, LaTeX2e, requires packages rotating.sty and curves.sty from CTA

Critical region of the finite temperature chiral transition

We study a Yukawa theory with spontaneous chiral symmetry breaking and with a large number N of fermions near the finite temperature phase transition. Critical properties in such a system can be described by the mean field theory very close to the transition point. We show that the width of the region where non-trivial critical behavior sets in is suppressed by a certain power of 1/N. Our Monte Carlo simulations confirm these analytical results. We discuss implications for the chiral phase transition in QCD.Comment: 18 page

Mesonic Wavefunctions in the three-dimensional Gross-Neveu model

We present results from a numerical study of bound state wavefunctions in the (2+1)-dimensional Gross-Neveu model with staggered lattice fermions at both zero and nonzero temperature. Mesonic channels with varying quantum numbers are identified and analysed. In the strongly coupled chirally broken phase at T=0 the wavefunctions expose effects due to varying the interaction strength more effectively than straightforward spectroscopy. In the weakly coupled chirally restored phase information on fermion - antifermion scattering is recovered. In the hot chirally restored phase we find evidence for a screened interaction. The T=0 chirally symmetric phase is most readily distinguished from the symmetric phase at high T via the fermion dispersion relation.Comment: 18 page

Risk-Sensitive Resource Defense in a Territorial Reef Fish

As coral reefs are home to dense aggregations of a variety of species, aggressive territoriality is often a critical component of individual behavior. Identification and assessment of the risk posed by intruders is crucial to defending a territory, and fishes on coral reefs have been found to attend to body shape, body size, and coloration when responding to intruders. We examined the extent to which dusky damselfish (Stegastes adustus) discriminate among distinct categories of intruders by measuring the distance at which a fish attacks an intruder and the relative intensity and frequency of those attacks. We found that S. adustus discriminated among perceived threats, attacking conspecifics more intensely and more often than egg-predators and herbivores, and showing a trend of attacking those groups more often than invertebrate-feeders, which do not compete with damselfish for resources. Furthermore, territory holders attacked initial-phase wrasses from a farther distance than terminal-phase wrasses, suggesting that they can discriminate among classes of individuals within a species other than their own. Dusky damselfish thus exhibit the ability to make fine distinctions among intruders in a diverse ecosystem