2,207 research outputs found
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 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
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
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
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
Mott-Anderson freeze-out and the strange matter "horn"
We discuss the -dependence of the ratio in heavy-ion
collisions (the "horn" effect) within a Mott-Anderson localization model for
chemical freeze-out. The different response of pion and kaon radii to the hot
and dense hadronic medium results in different freeze-out conditions. We
demonstrate within a simple model that this circumstance enhances the "horn"
effect relative to statistical models with universal chemical freeze-out.Comment: 8 pages, 4 figure
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.
On Non-Commutative U*(1) Gauge Models and Renormalizability
Based on our recent findings regarding (non-)renormalizability of
non-commutative U*(1) gauge theories [arxiv:0908.0467, arxiv:0908.1743] we
present the construction of a new type of model. By introducing a soft breaking
term in such a way that only the bilinear part of the action is modified, no
interaction between the gauge sector and auxiliary fields occurs. Demanding in
addition that the latter form BRST doublet structures, this leads to a
minimally altered non-commutative U*(1) gauge model featuring an IR damping
behavior. Moreover, the new breaking term is shown to provide the necessary
structure in order to absorb the inevitable quadratic IR divergences appearing
at one-loop level in theories of this kind. In the present paper we compute
Feynman rules, symmetries and results for the vacuum polarization together with
the one-loop renormalization of the gauge boson propagator and the three-point
functions.Comment: 20 pages, 4 figures; v2-v4: clarified several points, and minor
correction
Coexistence of color superconductivity and chiral symmetry breaking within the NJL model
The phase diagram for quark matter is investigated within a simple
Nambu-Jona-Lasinio model without vector correlations. It is found that the
phase structure in the temperature-density plane depends sensitively on the
parametrization of the model. We present two schemes of parametrization of the
model where within the first one a first order phase transition from a phase
with broken chiral symmetry to a color superconducting phase for temperatures
below the triple point at T_t= 55 MeV occurs whereas for the second one a
second order phase transition for temperatures below T_t = 7 MeV is found. In
the latter case, there is also a coexistence phase of broken chiral symmetry
with color superconductivity, which is a new finding within this class of
models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.Comment: LaTeX, 23 pages, 7 figures, new references and discussion added,
typos correcte
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