14,383 research outputs found
Quark matter in neutron stars
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
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
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
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
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?
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
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
A new, gapless two-flavor color superconducting phase that appears under
conditions of local charge neutrality and -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
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
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