15,202 research outputs found
The QCD Critical End Point in the Context of the Polyakov--Nambu--Jona-Lasinio Model
We investigate the phase diagram of the so-called
Polyakov--Nambu--Jona-Lasinio model at finite temperature and nonzero chemical
potential with three quark flavors. Chiral and deconfinement phase transitions
are discussed, and the relevant order-like parameters are analyzed. A special
attention is payed to the critical end point (CEP): the influence of the
strangeness on the location of the CEP is studied; also the strength of the
flavor-mixing interaction alters the CEP location, once when it becomes weaker
the CEP moves to low temperatures and can even disappear.Comment: Prepared for Strangeness in Quark Matter 2011, Sept. 18--24, Cracow,
Polan
Exploring the role of model parameters and regularization procedures in the thermodynamics of the PNJL model
The equation of state and the critical behavior around the critical end point
are studied in the context of the Polyakov--Nambu--Jona--Lasinio model. We
prove that a convenient choice of the model parameters is crucial to get the
correct description of isentropic trajectories. The physical relevance of the
effects of the regularization procedure is insured by the agreement with
general thermodynamic requirements. The results are compared with simple
thermodynamic expectations and lattice data.Comment: Talk given at XIII International Conference on Hadron Spectroscopy
(Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200
How parameters and regularization affect the PNJL model phase diagram and thermodynamic quantities
We explore the phase diagram and the critical behavior of QCD thermodynamic
quantities in the context of the so-called Polyakov--Nambu--Jona-Lasinio model.
We show that this improved field theoretical model is a successful candidate
for studying the equation of state and the critical behavior around the
critical end point. We argue that a convenient choice of the model parameters
is crucial to get the correct description of isentropic trajectories. The
effects of the regularization procedure in several thermodynamic quantities is
also analyzed. The results are compared with simple thermodynamic expectations
and lattice data.Comment: 27 pages, 7 figures, 4 tables; PRD versio
Restoration of U(1) symmetry and meson spectrum in hot or dense matter
We explore the effects of breaking and restoration of chiral and axial
symmetries using an extended three-flavor Nambu-Jona-Lasinio model that
incorporates explicitly the axial anomaly through the 't Hooft interaction. We
implement a temperature (density) dependence of the anomaly coefficient
motivated by lattice results for the topological susceptibility. The spectrum
of scalar and pseudoscalar mesons is analyzed bearing in mind the
identification of chiral partners and the study of its convergence. We also
concentrate on the behavior of the mixing angles that give us relevant
information on the issue under discussion. The results suggest that the axial
part of the symmetry is restored before the possible restoration of the full
U(3)U(3) chiral symmetry might occur.Comment: 9 pages, 5 figures. Talk given at Joint Meeting
Heidelberg-Liege-Paris-Rostock (HLPR 2004), Spa, Belgium, 16-18 Dec 200
Effects of the restoration of U(1) symmetry on pseudoscalar meson observables
We investigate the restoration of chiral SUSU and axial
U(1) symmetries, at finite temperature and density, in the framework of the
three flavor Nambu-Jona-Lasinio model with anomaly. We implement a temperature
(density) dependence of the anomaly coefficient motivated by lattice results
for the topological susceptibility and we discuss the restoration of symmetries
by analyzing the behavior of the mesonic chiral partners and of the mixing
angles. The results indicate that the axial part of the symmetry is restored
before the possible restoration of the full U(3)U(3) chiral symmetry
can occur.Comment: 4 pages, 1 figure. Contribution to Proc. Int. Europhysics Conf. on
High Energy Physics (HEP2005), 21-27.7.2005, Lisboa, Portuga
Interplay between chiral and axial symmetries in a SU(2) Nambu--Jona-Lasinio Model with the Polyakov loop
We consider a two flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model where the
Lagrangian includes an interaction term that explicitly breaks the U
anomaly. At finite temperature, the restoration of chiral and axial symmetries,
signaled by the behavior of several observables, is investigated. We compare
the effects of two regularizations at finite temperature, one of them, that
allows high momentum quarks states, leading to the full recovery of chiral
symmetry. From the analysis of the behavior of the topological susceptibility
and of the mesonic masses of the axial partners, it is found in the SU(2) model
that, unlike the SU(3) results, the recovery of the axial symmetry is not a
consequence of the full recovery of the chiral symmetry. Thus, one needs to use
an additional idea, by means of a temperature dependence of the anomaly
coefficient, that simulates instanton suppression effects.Comment: 21 pages, 5 figures; PRD versio
Vertebrate somite development and neural patterning
The segmentation of the axial skeleton and peripheral nervous system involves a complex integration of multiple patterning molecules. For the latter, axon-repelling molecules in the posterior half-sclerotome are particularly important. This study built on a previously performed mouse microarray screen for novel candidate genes in the posterior half-sclerotome. Multiple candidates were selected for whole-mount in situ hybridization in chick. Two were expressed in the posterior half-sclerotome: thrombin receptor (F2R) and fibronectin leucine rich transmembrane protein-2 (Flrt2). Flrt2 was selected for siRNA-mediated knockdown and a new in ovo transfection technique for somites successfully developed. Scrambled siRNA-transfection did not affect morphogenesis, somite patterning or axon guidance. However, Flrt2 siRNA-transfection resulted in defects in notochord, dermomyotome and neural tube morphogenesis, and in the de-fasciculation and mis-targeting of spinal axons into the posterior half-sclerotome and dermomyotome. Hence, Flrt2 may be a chemorepellent for spinal axons.
An unidentified peanut agglutinin (PNA)-binding glycoprotein in the posterior half-sclerotome was previously shown to repel spinal axons. In this project, the expression of a family of mucin-type O-glycosylation enzymes (which could glycosylate the PNA-binding protein) was investigated by whole-mount in situ hybridization in chick, but none was differentially expressed in the posterior half-sclerotome. One candidate for the PNA-binding glycoprotein, Presenilin1, was investigated because of previously published loss of spinal nerve segmentation in Presenilin1 mutants. However, analysis of Presenilin1-hypomorphic mutant mouse embryos showed this was not the PNA-binding molecule. Live-immunostaining for a second candidate, prolyl 4-hydroxylase, beta polypeptide (P4HB), showed its expression coincided with PNA-binding at the surface of posterior half-sclerotome cells. P4HB siRNA-transfection into somites reduced PNA binding and disrupted spinal axon segmentation and expression of a posterior sclerotome marker, Uncx4.1. Overall, these results suggest that P4HB is a strong candidate to be the key PNA-binding glycoprotein in the posterior half-sclerotome that repels spinal axons
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