2,951 research outputs found
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.
Improving the staggered quark action to reduce flavour symmetry violations
We investigate a class of actions for lattice QCD with staggered quarks aimed
at reducing the flavour symmetry violations associated with using staggered
fermions. These actions replace the gauge field link fields in the quark action
with covariantly smeared fields. As such they are an extension of actions
considered by the MILC collaboration. We show that such actions systematically
reduce flavour symmetry violations in the weak coupling limit. Using the mass
splitting between Goldstone and non-Goldstone pions as a measure of flavour
symmetry violations we find that these actions have considerably less flavour
symmetry violations than the standard staggered action, and represent an
improvement on what can be achieved with the MILC action, on quenched
configurations with .Comment: 3 pages, Latex using espcrc2.sty. 1 coloured postscript figure
included with epsffile. Talk presented by D.K.Sinclair at LATTICE'97,
Edinburgh, Scotlan
Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds
<p>A series of Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, <em>T<sub>C</sub></em>, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO<sub>6</sub> octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of <em>T<sub>C</sub></em>. The effects of A-site ionic radii on the temperatures of phase transitions in Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> were discussed. </p
Quark mass effects on the stability of hybrid stars
We perform a study of the possible existence of hybrid stars with color
superconducting quark cores using a specific hadronic model in a combination
with an NJL-type quark model. It is shown that the constituent mass of the
non-strange quarks in vacuum is a very important parameter that controls the
beginning of the hadron-quark phase transition. At relatively small values of
the mass, the first quark phase that appears is the two-flavor color
superconducting (2SC) phase which, at larger densities, is replaced by the
color-flavor locked (CFL) phase. At large values of the mass, on the other
hand, the phase transition goes from the hadronic phase directly into the CFL
phase avoiding the 2SC phase. It appears, however, that the only stable hybrid
stars obtained are those with the 2SC quark cores.Comment: 12 pages, 7 eps figures; v2: figures and table modified after
correction of a minor numerical mistake, discussion clarified, references
added, conclusions unchanged; version to appear in PL
Anyons in discrete gauge theories with Chern-Simons terms
We study the effect of a Chern-Simons term in a theory with discrete gauge
group H, which in (2+1)-dimensional space time describes (non-abelian) anyons.
As in a previous paper, we emphasize the underlying algebraic structure, namely
the Hopf algebra D(H). We argue on physical grounds that the addition of a
Chern-Simons term in the action leads to a non-trivial 3-cocycle on D(H).
Accordingly, the physically inequivalent models are labelled by the elements of
the cohomology group H^3(H,U(1)). It depends periodically on the coefficient of
the Chern-Simons term which model is realized. This establishes a relation with
the discrete topological field theories of Dijkgraaf and Witten. Some
representative examples are worked out explicitly.Comment: 18 page
Self-consistent parametrization of the two-flavor isotropic color-superconducting ground state
Lack of Lorentz invariance of QCD at finite quark chemical potential in
general implies the need of Lorentz non-invariant condensates for the
self-consistent description of the color-superconducting ground state.
Moreover, the spontaneous breakdown of color SU(3) in this state naturally
leads to the existence of SU(3) non-invariant non-superconducting expectation
values. We illustrate these observations by analyzing the properties of an
effective 2-flavor Nambu-Jona-Lasinio type Lagrangian and discuss the
possibility of color-superconducting states with effectively gapless fermionic
excitations. It turns out that the effect of condensates so far neglected can
yield new interesting phenomena.Comment: 16 pages, 3 figure
Neutron stars and the transition to color-superconducting quark matter
We explore the relevance of color superconductivity inside a possible quark
matter core for the bulk properties of neutron stars. For the quark phase we
use an Nambu--Jona-Lasinio (NJL) type model, extended to include diquark
condensates. For the hadronic phase, a microscopic many-body model is adopted,
with and without strangeness content. In our calculations, a sharp boundary is
assumed between the hadronic and the quark phases. For NJL model parameters
fitted to vacuum properties we find that no star with a pure quark core does
exist. Nevertheless the presence of color superconducting phases can lower the
neutron star maximum mass substantially. In some cases, the transition to quark
matter occurs only if color superconductivity is present. Once the quark phase
is introduced, the value of the maximum mass stays in any case below the value
of two solar masses.Comment: 11 pages, 3 figures, v2: minor corrections in the text, layout of the
figures improved, references added, v3: transition densities from hadronic to
quark matter added, version accepted for publication in PL
Quark matter in compact stars?
Ozel, in a recent reanalysis of EXO 0748-676 observational data
(astro-ph/0605106), concluded that quark matter probably does not exist in the
center of compact stars. We show that the data is actually consistent with the
presence of quark matter in compact stars.Comment: 4 pages, LaTeX; New title and overall rewrite to reflect version
published in Nature. Conclusions unchange
SO(10) Cosmic Strings and SU(3) Color Cheshire Charge
Certain cosmic strings that occur in GUT models such as can carry a
magnetic flux which acts nontrivially on objects carrying
quantum numbers. We show that such strings are non-Abelian Alice strings
carrying nonlocalizable colored ``Cheshire" charge. We examine claims made in
the literature that strings can have a long-range, topological
Aharonov-Bohm interaction that turns quarks into leptons, and observe that such
a process is impossible. We also discuss flux-flux scattering using a
multi-sheeted formalism.Comment: 37 Pages, 8 Figures (available upon request) phyzzx, iassns-hep-93-6,
itp-sb-93-6
Color Superconductivity in Asymmetric Matter
The influence of different chemical potential for different flavors on color
superconductivity is analyzed.
It is found that there is a first order transition as the asymmetry grows.
This transition proceeds through the formation of bubbles of low density,
flavor asymmetric normal phase inside a high density, superconducting phase
with a gap {\it larger} than the one found in the symmetric case. For small
fixed asymmetries the system is normal at low densities and superconducting
only above some critical density. For larger asymmetries the two massless
quarks system stays in the mixed state for arbitrarily high densities.Comment: 8 pages, 2 figure
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