QCD as a Quantum Link Model

QCD is constructed as a lattice gauge theory in which the elements of the link matrices are represented by non-commuting operators acting in a Hilbert space. The resulting quantum link model for QCD is formulated with a fifth Euclidean dimension, whose extent resembles the inverse gauge coupling of the resulting four-dimensional theory after dimensional reduction. The inclusion of quarks is natural in Shamir's variant of Kaplan's fermion method, which does not require fine-tuning to approach the chiral limit. A rishon representation in terms of fermionic constituents of the gluons is derived and the quantum link Hamiltonian for QCD with a U(N) gauge symmetry is expressed in terms of glueball, meson and constituent quark operators. The new formulation of QCD is promising both from an analytic and from a computational point of view.Comment: 27 pages, including three figures. ordinary LaTeX; Submitted to Nucl. Phys.

Small-sized magnesium cylinders influence subchondral bone quality in osteoarthritic rabbits an – in vivo pilot study

No optimal therapy exists to stop or cure chondral degeneration in osteoarthritis (OA). While the pathogenesis is unclear, there is consensus on the etiological involvement of both articular cartilage and subchondral bone. Compared to original bone, the substance of sclerotic bone is mechanically less solid. The osteoproliferative effect of Mg has been shown repeatedly during development of Mg-based osteosynthesis implants. The aim of the present study was to examine the influence of implanted high-purity Mg cylinders on subchondral bone quality in a rabbit OA model. 10 New Zealand White rabbits received into the knee either 20 empty drill holes or 20 drill holes, which were additionally filled with one Mg cylinder each. Follow-up was at 8 weeks. Micro-computed tomography (µCT) was performed. After euthanasia, cartilage condition was determined, bone samples were collected and processed for histological evaluation and elemental imaging by micro-Xray fluorescence spectrometry (µXRF). Articular cartilage collected post-mortem showed different stages of lesions, from mild alterations up to exposed subchondral bone, which tended to be slightly lower in animals with implanted Mg cylinders. µCT showed significantly increased bone volume in the Mg group. Also, histological evaluation revealed distinct differences. While right, operated limbs did not show any significant difference, left, non-operated controls showed significantly less changes in articular cartilage in the Mg group. A distinct influence of implanted cylinders of pure Mg on subchondral bone of osteoarthritic rabbits was shown. Subsequent evaluations, including other time points and alternative alloys, will show if this could alter OA progression

Quantum vs. Geometric Disorder in a Two-Dimensional Heisenberg Antiferromagnet

We present a numerical study of the spin-1/2 bilayer Heisenberg antiferromagnet with random interlayer dimer dilution. From the temperature dependence of the uniform susceptibility and a scaling analysis of the spin correlation length we deduce the ground state phase diagram as a function of nonmagnetic impurity concentration p and bilayer coupling g. At the site percolation threshold, there exists a multicritical point at small but nonzero bilayer coupling g_m = 0.15(3). The magnetic properties of the single-layer material La_2Cu_{1-p}(Zn,Mg)_pO_4 near the percolation threshold appear to be controlled by the proximity to this new quantum critical point.Comment: minor changes, updated figure

Quantum magnetism in the stripe phase: bond- versus site order

It is argued that the spin dynamics in the charge-ordered stripe phase might be revealing with regards to the nature of the anomalous spin dynamics in cuprate superconductors. Specifically, if the stripes are bond ordered much of the spin fluctuation will originate in the spin sector itself, while site ordered stripes require the charge sector as the driving force for the strong quantum spin fluctuations.Comment: 4 pages, 3 figures, LaTe

Exact, Complete, and Universal Continuous-Time Worldline Monte Carlo Approach to the Statistics of Discrete Quantum Systems

We show how the worldline quantum Monte Carlo procedure, which usually relies on an artificial time discretization, can be formulated directly in continuous time, rendering the scheme exact. For an arbitrary system with discrete Hilbert space, none of the configuration update procedures contain small parameters. We find that the most effective update strategy involves the motion of worldline discontinuities (both in space and time), i.e., the evaluation of the Green's function. Being based on local updates only, our method nevertheless allows one to work with the grand canonical ensemble and non-zero winding numbers, and to calculate any dynamic correlation function as easily as expectation values of, e.g., total energy. The principles found for the update in continuous time generalize to any continuous variables in the space of discrete virtual transitions, and in principle also make it possible to simulate continuous systems exactly.Comment: revtex, 14 pages, 6 figures, published version (modified and extended

Confinement in the Deconfined Phase: A numerical study with a cluster algorithm

We have previously found analytically a very unusual and unexpected form of confinement in SU(3) Yang-Mills theory. This confinement occurs in the deconfined phase of the theory. The free energy of a single static test quark diverges, even though it is contained in deconfined bulk phase and there is no QCD string present. This phenomenon occurs in cylindrical volumes with a certain choice of spatial boundary conditions. We examine numerically an effective model for the Yang-Mills theory and, using a cluster algorithm, we observe this unusual confinement. We also find a new way to determine the interface tension of domain walls separating distinct bulk phases.Comment: LaTex, 14 pages, 4 figure

Critical exponents of the quantum phase transition in a planar antiferromagnet

We have performed a large scale quantum Monte Carlo study of the quantum phase transition in a planar spin-1/2 Heisenberg antiferromagnet with CaV4O9 structure. We obtain a dynamical exponent z=1.018+/-0.02. The critical exponents beta, nu and eta agree within our errors with the classical 3D O(3) exponents, expected from a mapping to the nonlinear sigma model. This confirms the conjecture of Chubukov, Sachdev and Ye [Phys. Rev. B 49, 11919 (1994)] that the Berry phase terms in the planar Heisenberg antiferromagnet are dangerously irrelevant.Comment: 5 pages including 4 figures; revised version: some minor changes and added reference

Looking at the gluon moment of the nucleon with dynamical twisted mass fermions

7 pages, 3 figures, talk given at the 31st International Symposium on Lattice Field Theory (Lattice 2013), July 29-August 3 2013, Mainz, GermanyTo understand the structure of hadrons it is important to know the PDF of their constituents, the quarks and gluons. In our work we aim to compute the first moment of the gluon PDF $\langle x \rangle_g$ for the nucleon. We follow two possible approaches in order to extract the gluon moment: the Feynman-Hellmann theorem and a direct method with smearing of the gluon operator. We present preliminary results computed on $24^3 \times 48$ lattices for the case where the Feynman-Hellman theorem is used and $32^3 \times 64$ lattices for the direct method, employing $N_f=2+1+1$ maximally twisted mass fermions

A culture-independent method for studying transfer of IncI1 plasmids from wild-type Escherichia coli in complex microbial communities

IncI1 plasmids play a central role in the transfer of antimicrobial resistance genes among Enterobacteriaceae in animals and humans. Knowledge on the dynamics of IncI1 plasmid transfer is limited, mainly due to lack of culture-independent methods that can quantify donor strain survival and plasmid transfer in complex microbial communities. The aim of this study was to develop a culture-independent method to study the dynamics of IncI1 plasmids transfer by fluorescence-activated cell sorting. We genetically modified three wild-type Escherichia coli of animal (n = 2) and human (n = 1) origin carrying blaCMY-2 or blaCTX-M-1 on two epidemic IncI1 plasmids (pST12 and pST7). Non-coding regions on the chromosome and on the IncI1 plasmid of each strain were tagged with mCherry (red) and GFPmut3 (green) fluorescent proteins, respectively, using lambda recombineering. A gene cassette expressing mCherry and lacIq was inserted into the chromosome, whereas the plasmid was marked with a GFPmut3 cassette with LacIq repressible promoter. Therefore, gfpmut3 was repressed in donor strains but expressed in recipient strains acquiring the plasmids. We demonstrated that genetic engineering of the strains did not affect the growth rate and plasmid transfer-ability in filter and broth matings. A proof-of-concept experiment using the CoMiniGut, an in vitro model of the colon, proved the validity of our method for studying the survival of wild-type E. coli and horizontal transfer of IncI1 plasmids under different pH and oxygen conditions. The dual-labeling method by fluorescent proteins is useful to determine persistence of exogenous E. coli and transfer dynamics of IncI1 plasmids in microbial communities