40 research outputs found
Thermodynamics of a three-flavor nonlocal Polyakov--Nambu--Jona-Lasinio model
The present work generalizes a nonlocal version of the Polyakov loop-extended
Nambu and Jona-Lasinio (PNJL) model to the case of three active quark flavors,
with inclusion of the axial U(1) anomaly. Gluon dynamics is incorporated
through a gluonic background field, expressed in terms of the Polyakov loop.
The thermodynamics of the nonlocal PNJL model accounts for both chiral and
deconfinement transitions. Our results obtained in mean-field approximation are
compared to lattice QCD results for quark flavors. Additional
pionic and kaonic contributions to the pressure are calculated in random phase
approximation. Finally, this nonlocal 3-flavor PNJL model is applied to the
finite density region of the QCD phase diagram. It is confirmed that the
existence and location of a critical point in this phase diagram depends
sensitively on the strength of the axial U(1) breaking interaction.Comment: 31 pages, 15 figures, minor changes compared to v
Nonlocal quark model beyond mean field and QCD phase transition
A nonlocal chiral quark model is consistently extended beyond mean field
using a strict 1/Nc expansion scheme. The parameters of the nonlocal model are
refitted to the physical values of the pion mass and the weak pion decay
constant. The size of the 1/Nc correction to the quark condensate is carefully
studied in the nonlocal and the usual local Nambu-Jona-Lasinio models. It is
found that even the sign of the corrections can be different. This can be
attributed to the mesonic cut-off of the local model. It is also found that the
1/Nc corrections lead to a lowering of the temperature of the chiral phase
transition in comparison with the mean-field result. On the other hand, near
the phase transition the 1/Nc expansion breaks down and a non-perturbative
scheme for the inclusion of mesonic correlations is needed in order to describe
the phase transition point.Comment: 4 pages, 4 figures, talk at the 3rd Joint International Hadron
Structure'09 Conference, Tatranska Strba (Slovak Republic), Aug. 30-Sept. 3,
200
Towards finite density QCD with Taylor expansions
Convergence properties of Taylor expansions of observables, which are also
used in lattice QCD calculations at non-zero chemical potential, are analyzed
in an effective N_f = 2+1 flavor Polyakov-quark-meson model. A recently
developed algorithmic technique allows the calculation of higher-order Taylor
expansion coefficients in functional approaches. This novel technique is for
the first time applied to an effective N_f = 2+1 flavor Polyakov-quark-meson
model and the findings are compared with the full model solution at finite
densities. The results are used to discuss prospects for locating the QCD phase
boundary and a possible critical endpoint in the phase diagram.Comment: 11 pages, 6 figures; minor clarifying changes, version to be
published in Phys. Lett.
Spontaneous parity and charge-conjugation violations at real isospin and imaginary baryon chemical potentials
The phase structure of two-flavor QCD is investigated at real isospin and
imaginary quark chemical potentials by using the Polyakov-loop extended
Nambu--Jona-Lasinio model. In the region, parity symmetry is spontaneously
broken by the pion superfluidity phase transition, whereas charge-conjugation
symmetry is spontaneously violated by the Roberge-Weiss transition. The chiral
(deconfinement) crossover at zero isospin and quark chemical potentials is a
remnant of the parity (charge-conjugation) violation. The interplay between the
parity and charge-conjugation violations are analyzed, and it is investigated
how the interplay is related to the correlation between the chiral and
deconfinement crossovers at zero isospin and quark chemical potentials.Comment: 12 pages, 18 figures. Typos were revised. Symbols /P and /C were
added in Figures 8a and 8b. Colors of the figures were changed. Some
sentences were added and revise
Thermodynamics of the PNJL model
QCD thermodynamics is investigated by means of the Polyakov-loop-extended
Nambu Jona-Lasinio (PNJL) model, in which quarks couple simultaneously to the
chiral condensate and to a background temporal gauge field representing
Polyakov loop dynamics. The behaviour of the Polyakov loop as a function of
temperature is obtained by minimizing the thermodynamic potential of the
system. A Taylor series expansion of the pressure is performed. Pressure
difference and quark number density are then evaluated up to sixth order in
quark chemical potential, and compared to the corresponding lattice data. The
validity of the Taylor expansion is discussed within our model, through a
comparison between the full results and the truncated ones.Comment: 6 pages, 5 figures, Talk given at the Workshop for Young Scientists
on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (Hot Quarks
2006), Villasimius, Italy, 15-20 May 200
The phase structure of the Polyakov--quark-meson model beyond mean field
The Polyakov-extended quark-meson model (PQM) is investigated beyond
mean-field. This represents an important step towards a fully dynamical QCD
computation. Both the quantum fluctuations to the matter sector and the
back-reaction of the matter fluctuations to the QCD Yang-Mills sector are
included. Results on the chiral and confinement-deconfinement crossover/phase
transition lines and the location of a possible critical endpoint are
presented. Moreover, thermodynamic quantities such as the pressure and the
quark density are discussed.Comment: 12 pages, 11 figure
Oleate but not stearate induces the regulatory phenotype of myeloid suppressor cells
Tumor infiltrating myeloid cells play contradictory roles in the tumor
development. Dendritic cells and classical activated macrophages support anti-
tumor immune activity via antigen presentation and induction of pro-
inflammatory immune responses. Myeloid suppressor cells (MSCs), for instance
myeloid derived suppressor cells (MDSCs) or tumor associated macrophages play
a critical role in tumor growth. Here, treatment with sodium oleate, an
unsaturated fatty acid, induced a regulatory phenotype in the myeloid
suppressor cell line MSC-2 and resulted in an increased suppression of
activated T cells, paralleled by increased intracellular lipid droplets
formation. Furthermore, sodium oleate potentiated nitric oxide (NO) production
in MSC-2, thereby increasing their suppressive capacity. In primary polarized
bone marrow cells, sodium oleate (C18:1) and linoleate (C18:2), but not
stearate (C18:0) were identified as potent FFA to induce a regulatory
phenotype. This effect was abrogated in MSC-2 as well as primary cells by
specific inhibition of droplets formation while the inhibition of de novo FFA
synthesis proved ineffective, suggesting a critical role for exogenous FFA in
the functional induction of MSCs. Taken together our data introduce a new
unsaturated fatty acid-dependent pathway shaping the functional phenotype of
MSCs, facilitating the tumor escape from the immune system