14,279 research outputs found

    Quark matter in neutron stars

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    According to quantum chromodynamics, matter at ultra-high density and low temperature is a quark liquid, with a condensate of Cooper pairs of quarks near the Fermi surface ("color superconductivity"). This paper reviews the physics of color superconductivity, and discusses some of the proposed signatures by which we might detect quark matter in neutron stars.Comment: 8 pages, 3 figures; To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee. v2: typo corrected, line numbers remove

    Neutral color-spin locking phase in neutron stars

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    We present results for the spin-1 color-spin locking phase (CSL) using a NJL-type model in two flavor quark matter for compact stars applications. The CSL condensate is flavor symmetric and therefore charge and color neutrality can easily be satisfied. We find small energy gaps ~1 MeV, which make the CSL matter composition and the EoS not very different from the normal quark matter phase. We keep finite quark masses in our calculations and obtain no gapless modes that could have strong consequences in the late cooling of neutron stars. Finally, we show that the region of the phase diagram relevant for neutron star cores, when asymmetric flavor pairing is suppressed, could be covered by the CSL phase.Comment: 3 pages, 4 figures, contribution talk to the IVth International Conference on Quarks and Nuclear Physics(QNP06), Madrid, Spain, 5-10 Jun 200

    Color-Flavor Locking and Chiral Symmetry Breaking in High Density QCD

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    We propose a symmetry breaking scheme for QCD with three massless quarks at high baryon density wherein the color and flavor SU(3)_color times SU(3)_L times SU(3)_R symmetries are broken down to the diagonal subgroup SU(3)_{color+L+R} by the formation of a condensate of quark Cooper pairs. We discuss general properties that follow from this hypothesis, including the existence of gaps for quark and gluon excitations, the existence of Nambu-Goldstone bosons which are excitations of the diquark condensate, and the existence of a modified electromagnetic gauge interaction which is unbroken and which assigns integral charge to the elementary excitations. We present mean-field results for a Hamiltonian in which the interaction between quarks is modelled by that induced by single-gluon exchange. We find gaps of order 10-100 MeV for plausible values of the coupling. We discuss the effects of nonzero temperature, nonzero quark masses and instanton-induced interactions on our results.Comment: 17 pages, LaTeX. Factors of 2 corrected, figs and tables updated accordingl

    Mixed phases of color superconducting quark matter

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    We examine electrically and color neutral quark matter in beta-equilibrium focusing on the possibility of mixed phases between different color superconducting phases. To that end we apply the Gibbs criterion to ensure phase equilibrium and discuss the external conditions under which these mixed phases can occur. Neglecting surface and Coulomb effects we find a rich structure of different mixed phases with up to four components, including 2SC and CFL matter as well as more ``exotic'' components, like a phase with us- and ds-pairing but without ud-pairing. Preliminary estimates indicate, however, that the mixed phases become unstable if surface and Coulomb effects are included.Comment: 22 pages, 9 figures, v2: minor changes in the text, version to appear in Nucl. Phys.

    Quantum Field Theory of Nonabelian Strings and Vortices

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    We develop an operator formalism for investigating the properties of nonabelian cosmic strings (and vortices) in quantum field theory. Operators are constructed that introduce classical string sources and that create dynamical string loops. The operator construction in lattice gauge theory is explicitly described, and correlation functions are computed in the strong--coupling and weak--coupling limits. These correlation functions are used to study the long--range interactions of nonabelian strings, taking account of charge--screening effects due to virtual particles. Among the phenomena investigated are the Aharonov--Bohm interactions of strings with charged particles, holonomy interactions between string loops, string entanglement, the transfer of ``Cheshire charge'' to a string loop, and domain wall decay via spontaneous string nucleation. We also analyze the Aharonov--Bohm interactions of magnetic monopoles with electric flux tubes in a confining gauge theory. We propose that the Aharonov--Bohm effect can be invoked to distinguish among various phases of a nonabelian gauge theory coupled to matter.Comment: (82 pp

    Critical Literacy and Second Language Learning in the Mainstream Classroom: An Elusive Nexus?

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    Critical Literacy (CL) is now a core component of Queensland secondary school English programs. These programs are delivered to a significant number of students from Non-English speaking backgrounds (NESB) whose linguistic and cultural resources are diverse and not necessarily representative of mainstream high school cultural capital (Bourdieu 1990). In response to the current emphasis on CL, it is vital for English as a Second Language (ESL) educators to identify the points of contention as well as the possibilities for promoting critical engagement with texts with adolescent ESL learners and to seek to create pedagogy that reflects the critical needs and capacities of these learners. This paper outlines the version of CL in secondary schools as theorised by a number of Australian researchers; discusses the relevance and importance of CL to NESB learners and finally raises a number of issues that need resolving if such learners are to be provided with a well-rounded literacy education amid contemporary Australian social relations and textual practice

    Ginzburg-Landau approach to the three flavor LOFF phase of QCD

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    We explore, using a Ginzburg-Landau expansion of the free energy, the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors, using the NJL four-fermion coupling to mimic gluon interactions. We find that, below the point where the QCD homogeneous superconductive phases should give way to the normal phase, Cooper condensation of the pairs u-s and d-u is possible, but in the form of the inhomogeneous LOFF pairing.Comment: 8 pages, 4 figures. Eq. (20) corrected. As a consequence figures have been modified to show only the solution with parallel total momenta of the us, ud pairs, as the other configurations are suppressed. Main conclusions of the paper are unchange

    Gapless two-flavor color superconductor

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    A new, gapless two-flavor color superconducting phase that appears under conditions of local charge neutrality and ÎČ\beta-equilibrium is revealed. In this phase, the symmetry of the ground state is the same as in the conventional two-flavor color superconductor. In the low-energy spectrum of this phase, however, there are only two gapped fermionic quasiparticles, and the other four quasiparticles are gapless. The origin and the basic properties of the gapless two-flavor color superconductor are discussed. This phase is a natural candidate for quark matter in cores of compact stars.Comment: 6 pages, 4 figures. 1 reference and 1 figure are added; the discussion of the effective potential properties is extende

    Color superconductivity: Continuity of quark and hadron matter, the role of the strange quark mass, and perturbative results

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    We summarize some recent results on the structure of QCD at very high baryon density.Comment: 4 pages, to appear in the proceedings of Quark Matter 9