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

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.

Strangeness in the cores of neutron stars

The measurement of the mass 1.97 +/- 0.04 M_sun for PSR J1614-2230 provides a new constraint on the equation of state and composition of matter at high densities. In this contribution we investigate the possibility that the dense cores of neutron stars could contain strange quarks either in a confined state (hyperonic matter) or in a deconfined one (strange quark matter) while fulfilling a set of constraints including the new maximum mass constraint. We account for the possible appearance of hyperons within an extended version of the density-dependent relativistic mean-field model, including the phi-meson interaction channel. Deconfined quark matter is described by the color superconducting three-flavor NJL model.Comment: 6 pages, 2 figures, contribution to "Strangeness in Quark Matter 2011", Cracow, September 18-24, 201

Pseudoscalar Meson Nonet at Zero and Finite Temperature

Theoretical understanding of experimental results from relativistic heavy-ion collisions requires a microscopic approach to the behavior of QCD n-point functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger equations, properly generalized within the Matsubara formalism. The convergence of sums over Matsubara modes is studied. The technical complexity of finite-temperature calculations mandates modeling. We present a model where the QCD interaction in the infrared, nonperturbative domain, is modeled by a separable form. Results for the mass spectrum of light quark flavors (u, d, s) and for the pseudoscalar bound-state amplitudes at finite temperature are presented.Comment: 14 pages, 11 figures, accepted for publication in Physics of Particles and Nuclei Letters, based on invited lectures at "Dense Matter In Heavy Ion Collisions and Astrophysics", 21.08-01.09 2006, Dubna, Russi

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

Finite-size effects at the hadron-quark transition and heavy hybrid stars

We study the role of finite-size effects at the hadron-quark phase transition in a new hybrid equation of state constructed from an ab-initio Br\"uckner-Hartree-Fock equation of state with the realistic Bonn-B potential for the hadronic phase and a covariant non-local Nambu--Jona-Lasinio model for the quark phase. We construct static hybrid star sequences and find that our model can support stable hybrid stars with an onset of quark matter below $2 M_\odot$ and a maximum mass above $2.17 M_\odot$ in agreement with recent observations. If the finite-size effects are taken into account the core is composed of pure quark matter. Provided that the quark vector channel interaction is small, and the finite size effects are taken into account, quark matter appears at densities 2-3 times the nuclear saturation density. In that case the proton fraction in the hadronic phase remains below the value required by the onset of the direct URCA process, so that the early onset of quark matter shall affect on the rapid cooling of the star.Comment: version to match the one published in PR