Tamás Kovács

Inverse magnetic catalysis and the Polyakov loop

A bstractWe study the physical mechanism of how an external magnetic field influences the QCD quark condensate. Two competing mechanisms are identified, both relying on the interaction between the magnetic field and the low quark modes. While the coupling to valence quarks enhances the condensate, the interaction with sea quarks suppresses it in the transition region. The latter “sea effect” acts by ordering the Polyakov loop and, thereby, reduces the number of small Dirac eigenmodes and the condensate. It is most effective around the transition temperature, where the Polyakov loop effective potential is flat and a small correction to it by the magnetic field can have a significant effect. Around the critical temperature, the sea suppression overwhelms the valence enhancement, resulting in a net suppression of the condensate, named inverse magnetic catalysis. We support this physical picture by lattice simulations including continuum extrapolated results on the Polyakov loop as a function of temperature and magnetic field. We argue that taking into account the increase in the Polyakov loop and its interaction with the low-lying modes is essential to obtain the full physical picture, and should be incorporated in effective models for the description of QCD in magnetic fields in the transition region.

Improving the chiral properties of lattice fermions

The chiral properties of lattice fermions can be improved by altering either their fermion-gauge coupling or the pure gauge part of the action (or both). Using both perturbation theory and nonperturbative simulation, we compare a simple alteration of the gauge action (which encompasses the Wilson, Symanzik, Iwasaki, and DBW2 actions), and HYP-blocked links in the fermion action. Perturbative tests include calculations of the potential, flavor-changing quark scattering amplitudes, and matching factors for currents. Non-perturbative tests include the potential, measurements of flavor symmetry breaking for staggered fermions, the behavior of topological objects, and properties of overlap actions. Our results display the bad properties of these actions as well as their good ones.

EGFR and ErbB2 are functionally coupled to CD44 and regulate shedding, internalization and motogenic effect of CD44

Activation of the ErbB family of receptor tyrosine kinases is involved in a range of human cancers. Transmembrane signaling mediated by ErbB proteins is stimulated by peptide growth factors and is blocked by monoclonal antibodies such as trastuzumab and pertuzumab. ErbB receptors exert their function in conjunction with non-ErbB proteins, e.g. CD44. Here we show that epidermal growth factor (EGF) and heregulin induce CD44 shedding in JIMT-1, an ErbB2-overexpressing cell line resistant to trastuzumab, accompanied by internalization and intramembrane proteolysis of CD44 and enhanced cellular motility. These effects of EGF and heregulin are blocked by pertuzumab. Trastuzumab inhibits the heregulin- and hyaluronan oligosaccharide-induced shedding and internalization of CD44 and their motogenic effect. Trastuzumab also blocks CD44 shedding from JIMT-1 xenograft tumors in vivo. At the same time the internalization rate of trastuzumab is increased by hyaluronan oligosaccharide treatment in vitro. Our experiments point to an unexpected, but potentially important mechanism of action of ErbB receptor-targeted monoclonal antibodies used in the treatment of cancer.

Investigating and optimizing the chiral properties of lattice fermion actions

We study exceptional modes of both the Wilson and the clover action in order to understand why quenched clover spectroscopy suffers so severely from exceptional configurations. We show that a large clover coefficient can make the exceptional modes extremely localized and thus very sensitive to short distance fluctuations. We contrast this with the case of the Wilson action where exceptional modes correspond to large instantons. These modes are broadly extended and suffer much less from discretization errors.Abstract We study exceptional modes of both the Wilson and the clover action in order to understand why quenched clover spectroscopy suffers so severely from exceptional configurations. We show that, in contrast to the case of the Wilson action, a large clover coefficient can make the exceptional modes extremely localized and thus very sensitive to short distance fluctuations. We describe a way to optimize the chiral behavior of Wilson-type lattice fermion actions by studying their low energy real eigenmodes. We find a candidate action, the clover action with fat links with a tuned clover term. We present a calculation of spectroscopy and matrix elements at Wilson gauge coupling β = 5.7. When compared to simulations with the standard (non-perturbatively improved) clover action at small lattice spacing, the action shows good scaling behavior, with an apparent great reduction in the number of exceptional configurations.

The role of actin and myosin during spermatogenesis

Spermatogenesis is a transitionary process in which the diploid spermatogonia transform into haploid mature spermatozoa. Actin and myosin have been implicated in various aspects during spermatogenesis. Actin is present in the form of monomer, oligomer and polymer within cells, the latter is called microfilament. There are five actin-containing structures during spermatogenesis, i.e., ectoplasmic specialization, acroplaxome, manchette in mammals, actin cones in Drosophila and acroframosome in Caridean shrimp. They are involved in the shaping and differentiating of spermatids. Along with spermatogenesis, the actin cytoskeletons show active remodeling in this process. Some actin binding or actin regulated proteins have been demonstrated to regulate dynamic changes of the actin-containing structures. Myosin, actin-dependent molecular motor, plays an important role during spermatogenesis, such as involving in acrosome biogenesis, vesicle transport, gene transcription and nuclear shaping. The actin cytoskeleton and actin binding/regulated proteins cooperate to facilitate spermatogenesis. In this review, we summarize the existing knowledge about the cytoskeletal structures consisting of actin, actin binding/regulated proteins and myosin during spermatogenesis.

Absence of correlations in the QCD dirac spectrum at high temperature.

I propose a simple model of the distribution of the small eigenvalues of the QCD Dirac operator well above the finite temperature phase transition where chiral symmetry is restored and the spectral density at zero vanishes. Assuming the absence of correlations between different regions of the low-lying spectrum I derive analytic formulas for the distribution of the first two eigenvalues. I find good agreement with data obtained using the overlap Dirac operator in quenched SU(2) lattice simulations. This suggests that if chiral symmetry is restored spectral correlations are not important and all the statistical properties of the spectrum are encoded in the spectral density.

PENTAQUARK HADRONS FROM LATTICE QCD

The present work is a summary of the status of lattice pentaquark calculations. After a pedagogic introduction to the basics of lattice hadron spectroscopy we give a critical comparison of results presently available in the literature. Special emphasis is put on presenting some of the possible pitfalls of these calculations. In particular we discuss at length the choice of the hadronic operators and the separation of genuine five-quark states from meson-baryon scattering states.

Poisson-random matrix transition in the QCD Dirac spectrum

At zero temperature the lowest part of the spectrum of the QCD Dirac operator is known to consist of delocalized modes that are described by random matrix statistics. In the present paper we show that the nature of these eigenmodes changes drastically when the system is driven through the finite temperature cross-over. The lowest Dirac modes that are delocalized at low temperature become localized on the scale of the inverse temperature. At the same time the spectral statistics changes from random matrix to Poisson statistics. We demonstrate this with lattice QCD simulations using 2+1 flavors of light dynamical quarks with physical masses. Drawing an analogy with Anderson transitions we also examine the mobility edge separating localized and delocalized modes in the spectrum. We show that it scales in the continuum limit and increases sharply with the temperature.

DNA flow cytometry of human spermatozoa: Consistent stoichiometric staining of sperm DNA using a novel decondensation protocol

Rapid flow cytometric measurement of the frequency of aneuploid human sperms is in increasing demand but development of an exploitable method is hindered by difficulties of stoichiometric staining of sperm DNA. An aggressive decondensation protocol is needed after which cell integrity still remains intact. We used flow cytometry to examine the effect of lithium diiodosalicylate (LIS, chaotropic agent) on fluorescence intensity of propidium iodide‐treated human spermatozoa from 10 normozoospermic men. When flow cytometric identification of diploid spermatozoa was achieved, validation was performed after sorting by three‐color FISH. In contrast with the extremely variable histograms of nondecondensed sperms, consistent identification of haploid and diploid spermatozoa was possible if samples were decondensed with LIS prior to flow cytometry. A 76‐fold enrichment of diploid sperms was observed in the sorted fractions by FISH. A significant correlation was found between the proportion of sorted cells and of diploid sperms by FISH. Application of LIS during the preparation of sperm for flow cytometry appears to ensure the stoichiometric staining of sperm DNA, making quantification of aneuploid sperm percentage possible. To our knowledge this is the first report in terms of separating spermatozoa with confirmedly abnormal chromosomal content. High correlation between the proportion of cells identified as having double DNA content by flow cytometry and diploid sperm by FISH allows rapid calculation of diploidy rate.

Universality and the QCD Anderson transition

We study the Anderson-type transition previously found in the spectrum of the QCD quark Dirac operator in the high-temperature, quark-gluon plasma phase. Using finite size scaling for the unfolded level spacing distribution, we show that in the thermodynamic limit there is a genuine mobility edge, where the spectral statistics changes from Poisson to Wigner-Dyson statistics in a nonanalytic way. We determine the correlation length critical exponent ν and find that it is compatible with that of the unitary Anderson model.