2,788 research outputs found
Positivity of High Density Effective Theory
We show that the effective field theory of low energy modes in dense QCD has
positive Euclidean path integral measure. The complexity of the measure of QCD
at finite chemical potential can be ascribed to modes which are irrelevant to
the dynamics at sufficiently high density. Rigorous inequalities follow at
asymptotic density. Lattice simulation of dense QCD should be possible using
the quark determinant calculated in the effective theory.Comment: 10 pages, Revised version, to appear in Rapid Communications of
Physical Review
A quark action for very coarse lattices
We investigate a tree-level O(a^3)-accurate action, D234c, on coarse
lattices. For the improvement terms we use tadpole-improved coefficients, with
the tadpole contribution measured by the mean link in Landau gauge.
We measure the hadron spectrum for quark masses near that of the strange
quark. We find that D234c shows much better rotational invariance than the
Sheikholeslami-Wohlert action, and that mean-link tadpole improvement leads to
smaller finite-lattice-spacing errors than plaquette tadpole improvement. We
obtain accurate ratios of lattice spacings using a convenient ``Galilean
quarkonium'' method.
We explore the effects of possible O(alpha_s) changes to the improvement
coefficients, and find that the two leading coefficients can be independently
tuned: hadron masses are most sensitive to the clover coefficient, while hadron
dispersion relations are most sensitive to the third derivative coefficient
C_3. Preliminary non-perturbative tuning of these coefficients yields values
that are consistent with the expected size of perturbative corrections.Comment: 22 pages, LaTe
Dense quark matter in compact stars
The densest predicted state of matter is colour-superconducting quark matter,
in which quarks near the Fermi surface form a condensate of Cooper pairs. This
form of matter may well exist in the core of compact stars, and the search for
signatures of its presence is an ongoing enterprise. Using a bag model of quark
matter, I discuss the effects of colour superconductivity on the mass-radius
relationship of compact stars, showing that colour superconducting quark matter
can occur in compact stars at values of the bag constant where ordinary quark
matter would not be allowed. The resultant ``hybrid'' stars with colour
superconducting quark matter interior and nuclear matter surface have masses in
the range 1.3-1.6 Msolar and radii 8-11 km. Once perturbative corrections are
included, quark matter can show a mass-radius relationship very similar to that
of nuclear matter, and the mass of a hybrid star can reach 1.8 \Msolar.Comment: 11 pages, for proceedings of SQM 2003 conference; references added,
abstract reworde
Illuminating Dense Quark Matter
We imagine shining light on a lump of cold dense quark matter, in the CFL
phase and therefore a transparent insulator. We calculate the angles of
reflection and refraction, and the intensity of the reflected and refracted
light. Although the only potentially observable context for this phenomenon
(reflection of light from and refraction of light through an illuminated quark
star) is unlikely to be realized, our calculation casts new light on the old
idea that confinement makes the QCD vacuum behave as if filled with a
condensate of color-magnetic monopoles.Comment: 4 pages, 1 figur
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
Strange Stars with a Density-Dependent Bag Parameter
We have studied strange quark stars in the framework of the MIT bag model,
allowing the bag parameter B to depend on the density of the medium. We have
also studied the effect of Cooper pairing among quarks, on the stellar
structure. Comparison of these two effects shows that the former is generally
more significant. We studied the resulting equation of state of the quark
matter, stellar mass-radius relation, mass-central-density relation,
radius-central-density relation, and the variation of the density as a function
of the distance from the centre of the star. We found that the
density-dependent B allows stars with larger masses and radii, due to
stiffening of the equation of state. Interestingly, certain stellar
configurations are found to be possible only if B depends on the density. We
have also studied the effect of variation of the superconducting gap parameter
on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in
Phys. Rev. (D
Breached Pairing Superfluidity at Finite Temperature and Density
A general analysis on Fermion pairing at finite temperature and density
between different species with mismatched Fermi surfaces is presented. Very
different from the temperature effect of BCS phase, the recently found breached
pairing phase resulted from density difference of the two species lies in a
region with calabash-like shape in the plane, and the most probable
temperature for the new phase's creation is finite but not zero.Comment: 5 papes, 5 figures. Comments are welcome to
[email protected]
Neutrino Propagation In Color Superconducting Quark Matter
We calculate the neutrino mean free path in color superconducting quark
matter, and employ it to study the cooling of matter via neutrino diffusion in
the superconducting phase as compared to a free quark phase. The cooling
process slows when quark matter undergoes a second order phase transition to a
superconducting phase at the critical temperature . Cooling subsequently
accelerates as the temperature decreases below . This will directly impact
the early evolution of a newly born neutron star should its core contain quark
matter. Consequently, there may be observable changes in the early neutrino
emission which would provide evidence for superconductivity in hot and dense
matter.Comment: 12 pages, 5 figure
Bulk viscosity in a cold CFL superfluid
We compute one of the bulk viscosity coefficients of cold CFL quark matter in
the temperature regime where the contribution of mesons, quarks and gluons to
transport phenomena is Boltzmann suppressed. In that regime dissipation occurs
due to collisions of superfluid phonons, the Goldstone modes associated to the
spontaneous breaking of baryon symmetry. We first review the hydrodynamics of
relativistic superfluids, and remind that there are at least three bulk
viscosity coefficients in these systems. We then compute the bulk viscosity
coefficient associated to the normal fluid component of the superfluid. In our
analysis we use Son's effective field theory for the superfluid phonon, amended
to include scale breaking effects proportional to the square of the strange
quark mass m_s. We compute the bulk viscosity at leading order in the scale
breaking parameter, and find that it is dominated by collinear splitting and
joining processes. The resulting transport coefficient is zeta=0.011 m_s^4/T,
growing at low temperature T until the phonon fluid description stops making
sense. Our results are relevant to study the rotational properties of a compact
star formed by CFL quark matter.Comment: 19 pages, 2 figures; one reference added, version to be published in
JCA
Effective Gap Equation for the Inhomogeneous LOFF Superconductive Phase
We present an approximate gap equation for different crystalline structures
of the LOFF phase of high density QCD at T=0. This equation is derived by using
an effective condensate term obtained by averaging the inhomogeneous condensate
over distances of the order of the crystal lattice size. The approximation is
expected to work better far off any second order phase transition. As a
function of the difference of the chemical potentials of the up and down
quarks, , we get that the octahedron is energetically favored from
to , where is the gap for
the homogeneous phase, while in the range the face
centered cube prevails. At a first order phase
transition to the normal phase occurs.Comment: 11 pages, 5 figure
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