2,018 research outputs found

### On NCQFT and dimensionless insertions

In these notes, we aim at a precise definition of the tree level action for
the noncommutative scalar and gauge field theories on four-dimensional
canonically deformed Euclidean space. As tools to achieve this goal we employ
power counting and normalization conditions.Comment: 10 page

### 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

### Nonlocality effects on spin-one pairing patterns in two-flavor color superconducting quark matter and compact stars applications

We study the influence of nonlocality in the interaction on two spin one
pairing patterns of two-flavor quark matter: the anisotropic blue color paring
besides the usual two color superconducting matter (2SCb), in which red and
green colors are paired, and the color spin locking phase (CSL). The effect of
nonlocality on the gaps is rather large and the pairings exhibit a strong
dependence on the form factor of the interaction, especially in the low density
region. The application of these small spin-one condensates for compact stars
is analyzed: the early onset of quark matter in the nonlocal models may help to
stabilize hybrid star configurations. While the anisotropic blue quark pairing
does not survive a big asymmetry in flavor space as imposed by the charge
neutrality condition, the CSL phase as a flavor independent pairing can be
realized as neutral matter in compact star cores. However, smooth form factors
and the missmatch between the flavor chemical potential in neutral matter make
the effective gaps of the order of magnitude $\simeq 10$ keV, and a more
systematic analysis is needed to decide whether such small gaps could be
consistent with the cooling phenomenology.Comment: 18 pages, 7 figures, corrected version with revised parameterizatio

### A New Approach to Non-Commutative U(N) Gauge Fields

Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction

### 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

### Mapping Deconfinement with a Compact Star Phase Diagram

We have found correlations between properties of the equation of state for
stellar matter with a phase transition at supernuclear densities and two
characteristic features of a "phase diagram" for rotating compact stars in the
angular velocity - baryon number plane: 1) the critical dividing line between
mono- and two-phase star configurations and 2) the maximum mass line. The
second line corresponds to the minimum mass function for black hole candidates
whereas the first one is observable by a population statistics, e.g. for
Z-sources in low-mass X-ray binaries. The observation of a population gap in
the mass distribution for the latter is suggested as an astrophysical
verification of the existence of a first order phase transition in QCD at high
densities such as the deconfinement.Comment: 4 pages, 2 figures, Contribution to Proceedings of Quark Matter 2002,
Nantes, July 18 - 24, 200

### Width of the QCD transition in a Polyakov-loop DSE model

We consider the pseudocritical temperatures for the chiral and deconfinement
transitions within a Polyakov-loop Dyson-Schwinger equation approach which
employs a nonlocal rank-2 separable model for the effective gluon propagator.
These pseudocritical temperatures differ by a factor of two when the quark and
gluon sectors are considered separately, but get synchronized and become
coincident when their coupling is switched on. The coupling of the
Polyakov-loop to the chiral quark dynamics narrows the temperature region of
the QCD transition in which chiral symmetry and deconfinement is established.
We investigate the effect of rescaling the parameter T_0 in the Polyakov-loop
potential on the QCD transition for both the logarithmic and polynomial forms
of the potential. While the critical temperatures vary in a similar way, the
width of the transition is stronger affected for the logarithmic potential. For
this potential the character of the transition changes from crossover to a
first order one when T_0 < 210 MeV, but it remains crossover in the whole range
of relevant T_0 values for the polynomial form.Comment: 10 pages, 6 figures, results for polynomial form of Polyakov-loop
potential included, references added, final version to appear in Phys. Rev.

### A formula for charmonium suppression

In this work a formula for charmonium suppression obtained by Matsui in 1989
is analytically generalized for the case of complex c-cbar potential described
by a 3-dimensional and isotropic time-dependent harmonic oscillator (THO). It
is suggested that under certain conditions the formula can be applied to
describe J/\psi suppression in heavy-ion collisions at CERN-SPS, RHIC, and LHC
with the advantage of analytical tractability.Comment: 4 pages, no figures, to appear in Phys. At. Nucl., vol. 7

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