Accessibility of color superconducting quark matter phases in heavy-ion collisions

We discuss a hybrid equation of state (EoS) that fulfills constraints for mass-radius relationships and cooling of compact stars. The quark matter EoS is obtained from a Polyakov-loop Nambu--Jona-Lasinio (PNJL) model with color superconductivity, and the hadronic one from a relativistic mean-field (RMF) model with density-dependent couplings (DD-RMF). For the construction of the phase transition regions we employ here for simplicity a Maxwell construction. We present the phase diagram for symmetric matter which exhibits two remarkable features: (1) a "nose"-like structure of the hadronic-to-quark matter phase border with an increase of the critical density at temperatures below T ~ 150 MeV and (2) a high critical temperature for the border of the two-flavor color superconducting (2SC) phase, T_c > 160 MeV. We show the trajectories of heavy-ion collisions in the plane of excitation energy vs. baryon density calculated using the UrQMD code and conjecture that for incident energies of 4 ... 8 A GeV as provided, e.g., by the Nuclotron-M at JINR Dubna or by lowest energies at the future heavy-ion collision experiments CBM@FAIR and NICA@JINR, the color superconducting quark matter phase becomes accessible.Comment: 5 pages, 1 figure, Poster presented at the XXVI. Max Born Symposium "Three Days of Strong Interactions", Wroclaw (Poland), July 9-11, 200

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

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

Heavy flavor kinetics at the hadronization transition

We investigate the in-medium modification of the charmonium breakup processes due to the Mott effect for light (pi, rho) and open-charm (D, D*) quark-antiquark bound states at the chiral/deconfinement phase transition. The Mott effect for the D-mesons effectively reduces the threshold for charmonium breakup cross sections, which is suggested as an explanation of the anomalous J/psi suppression phenomenon in the NA50 experiment. Further implications of finite-temperature mesonic correlations for the hadronization of heavy flavors in heavy-ion collisions are discussed.Comment: 4 pages, 2 figures, Contribution to SQM2001 Conference, submitted to J. Phys.

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