Thermodynamic instabilities in dynamical quark models with complex conjugate mass poles

We show that the CJT thermodynamic potential of dynamical quark models with a quark propagator represented by complex conjugate mass poles inevitably exhibits thermodynamic instabilities. We find that the minimal coupling of the quark sector to a Polyakov loop potential can strongly suppress but not completely remove such instabilities. This general effect is explicitly demonstrated in the framework of a covariant, chirally symmetric, effective quark model.Comment: Minor typos corrected, submitted versio

Lattice QCD at finite temperature: Evidence for calorons from the eigenvectors of the Dirac operator

We analyze the eigenvalues and eigenvectors of the staggered Dirac operator in quenched lattice QCD in the vicinity of the deconfinement phase transition using the L\"uscher-Weisz gauge action. The spectral and localization properties of the low-lying eigenmodes show characteristic differences between the Z_3 sectors above the critical temperature T_c. These findings can be interpreted in terms of calorons.Comment: Lattice2001(hightemp), 3 pages, 2 figure

γp\gamma p and γγ\gamma \gamma scattering from pˉp\bar{p}p, pppp forward amplitudes in a QCD eikonal model with a dynamical gluon mass

We examine the $\gamma p$ photoproduction and the hadronic $\gamma \gamma$ total cross sections by means of a QCD eikonal model with a dynamical infrared mass scale. In this model, where the dynamical gluon mass is the natural regulator for the tree level gluon-gluon scattering, the $\gamma p$ and $\gamma \gamma$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. We show that the validity of the cross section factorization relation $\sigma_{pp}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma \gamma}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $\gamma \gamma$ cross section data, and we discuss in detail the case of $\sigma (\gamma \gamma \to hadrons)$ data with $W_{\gamma \gamma} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) that the photon interacts as a hadron.Comment: 16 pages, 3 figures; misprints corrected; to appear in Phys. Rev.

Visualization of Endothelial Actin Cytoskeleton in the Mouse Retina

Angiogenesis requires coordinated changes in cell shape of endothelial cells (ECs), orchestrated by the actin cytoskeleton. The mechanisms that regulate this rearrangement in vivo are poorly understood - largely because of the difficulty to visualize filamentous actin (F-actin) structures with sufficient resolution. Here, we use transgenic mice expressing Lifeact-EGFP to visualize F-actin in ECs. We show that in the retina, Lifeact-EGFP expression is largely restricted to ECs allowing detailed visualization of F-actin in ECs in situ. Lifeact-EGFP labels actin associated with cell-cell junctions, apical and basal membranes and highlights actin-based structures such as filopodia and stress fiber-like cytoplasmic bundles. We also show that in the skin and the skeletal muscle, Lifeact-EGFP is highly expressed in vascular mural cells (vMCs), enabling vMC imaging. In summary, our results indicate that the Lifeact-EGFP transgenic mouse in combination with the postnatal retinal angiogenic model constitutes an excellent system for vascular cell biology research. Our approach is ideally suited to address structural and mechanistic details of angiogenic processes, such as endothelial tip cell migration and fusion, EC polarization or lumen formation

Heavy Quark diffusion from lattice QCD spectral functions

We analyze the low frequency part of charmonium spectral functions on large lattices close to the continuum limit in the temperature region $1.5\lesssim T/T_c\lesssim 3$ as well as for $T \simeq 0.75T_c$. We present evidence for the existence of a transport peak above $T_c$ and its absence below $T_c$. The heavy quark diffusion constant is then estimated using the Kubo formula. As part of the calculation we also determine the temperature dependence of the signature for the charmonium bound state in the spectral function and discuss the fate of charmonium states in the hot medium.Comment: 4 pages, Proceedings for Quark Matter 2011 Conference, May 23-28, 2011, Annecy, Franc