2,423 research outputs found
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
Color-Neutral Superconducting Quark Matter
We investigate the consequences of enforcing local color neutrality on the
color superconducting phases of quark matter by utilizing the
Nambu-Jona-Lasinio model supplemented by diquark and the t'Hooft six-fermion
interactions. In neutrino free matter at zero temperature, color neutrality
guarantees that the number densities of u, d, and s quarks in the
Color-Flavor-Locked (CFL) phase will be equal even with physical current quark
masses. Electric charge neutrality follows as a consequence and without the
presence of electrons. In contrast, electric charge neutrality in the less
symmetric 2-flavor superconducting (2SC) phase with ud pairing requires more
electrons than the normal quark phase. The free energy density cost of
enforcing color and electric charge neutrality in the CFL phase is lower than
that in the 2SC phase, which favors the formation of the CFL phase. With
increasing temperature and neutrino content, an unlocking transition occurs
from the CFL phase to the 2SC phase with the order of the transition depending
on the temperature, the quark and lepton number chemical potentials. The
astrophysical implications of this rich structure in the phase diagram,
including estimates of the effects from Goldstone bosons in the CFL phase, are
discussed.Comment: 20 pages, 4 figures; version to appear in Phys. Rev.
Quark description of nuclear matter
We discuss the role of an adjoint chiral condensate for color superconducting
quark matter. Its presence leads to color-flavor locking in two-flavor quark
matter. Color is broken completely as well as chiral symmetry in the two-flavor
theory with coexisting adjoint quark-antiquark and antitriplet quark-quark
condensates. The qualitative properties of this phase match the properties of
ordinary nuclear matter without strange baryons. This complements earlier
proposals by Schafer and Wilczek for a quark description of hadronic phases. We
show for a class of models with effective four-fermion interactions that
adjoint chiral and diquark condensates do not compete, in the sense that
simultaneous condensation occurs for sufficiently strong interactions in the
adjoint chiral channel.Comment: 15 pages, 3 figure
Illuminating interfaces between phases of a U(1) x U(1) gauge theory
We study reflection and transmission of light at the interface between
different phases of a U(1) x U(1) gauge theory. On each side of the interface,
one can choose a basis so that one generator is free (allowing propagation of
light), and the orthogonal one may be free, Higgsed, or confined. However, the
basis on one side will in general be rotated relative to the basis on the other
by some angle alpha. We calculate reflection and transmission coefficients for
both polarizations of light and all 8 types of boundary, for arbitrary alpha.
We find that an observer measuring the behavior of light beams at the boundary
would be able to distinguish 4 different types of boundary, and we show how the
remaining ambiguity arises from the principle of complementarity
(indistinguishability of confined and Higgs phases) which leaves observables
invariant under a global electric/magnetic duality transformation. We also
explain the seemingly paradoxical behavior of Higgs/Higgs and confined/confined
boundaries, and clarify some previous arguments that confinement must involve
magnetic monopole condensation.Comment: RevTeX, 12 page
Scalar meson in dynamical and partially quenched two-flavor QCD: lattice results and chiral loops
This is an exploratory study of the lightest non-singlet scalar
state on the lattice with two dynamical quarks. Domain Wall fermions are used
for both sea and valence quarks on a 16^3*32 lattice with an inverse lattice
spacing of 1.7 GeV. We extract the scalar meson mass 1.58(34) GeV from the
exponential time-dependence of the dynamical correlators with
and N_f=2. Since this statistical error-bar from dynamical correlators is
rather large, we analyze also the partially quenched lattice correlators with
not equal . They are positive for and
negative for . In order to understand this striking effect of
partial quenching, we derive the scalar correlator within the Partially
Quenched ChPT and find it describes lattice correlators well. The leading
unphysical contribution in Partially Quenched ChPT comes from the exchange of
the two pseudoscalar fields and is also positive for and
negative for at large t. After the subtraction of this
unphysical contribution from the partially quenched lattice correlators, the
correlators are positive and exponentially falling. The resulting scalar meson
mass 1.51(19) GeV from the partially quenched correlators is consistent with
the dynamical result and has appreciably smaller error-bar.Comment: 23 pages, 8 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
Mass Terms in Effective Theories of High Density Quark Matter
We study the structure of mass terms in the effective theory for
quasi-particles in QCD at high baryon density. To next-to-leading order in the
expansion we find two types of mass terms, chirality conserving
two-fermion operators and chirality violating four-fermion operators. In the
effective chiral theory for Goldstone modes in the color-flavor-locked (CFL)
phase the former terms correspond to effective chemical potentials, while the
latter lead to Lorentz invariant mass terms. We compute the masses of Goldstone
bosons in the CFL phase, confirming earlier results by Son and Stephanov as
well as Bedaque and Sch\"afer. We show that to leading order in the coupling
constant there is no anti-particle gap contribution to the mass of
Goldstone modes, and that our results are independent of the choice of gauge.Comment: 22 pages, 4 figure
Superdense Matter
We review recent work on the phase structure of QCD at very high baryon
density. We introduce the phenomenon of color superconductivity and discuss the
use of weak coupling methods. We study the phase structure as a function of the
number of flavors and their masses. We also introduce effective theories that
describe low energy excitations at high baryon density. Finally, we study the
possibility of kaon condensation at very large baryon density.Comment: 13 pages, talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; to appear
in the proceeding
Meson Exchange Effect on Color Superconductivity
We investigate the effects of pion and gluon exchanges on the formation of
two-flavor color superconductivity at moderate density, . The
chiral quark model proposed by Manohar and Georgi containing pions as well as
gluons is employed to show that the pion exchange reduces substantially the
value of the superconducting gap gotten with the gluon exchange only. It turns
out that the pion exchanges produce a repulsion between quark-quark pair in a
spin and isospin singlet state.
We suggest that the phase consisiting of pions, gluons and quarks is one of
the candidates of in-medium QCD phase at moderate density.Comment: 8 pages, 1 figure, minor correction
Bulk viscosity in the nonlinear and anharmonic regime of strange quark matter
The bulk viscosity of cold, dense three-flavor quark matter is studied as a
function of temperature and the amplitude of density oscillations. The study is
also extended to the case of two different types of anharmonic oscillations of
density. We point several qualitative effects due to the anharmonicity,
although quantitatively they appear to be relatively small. We also find that,
in most regions of the parameter space, with the exception of the case of a
very large amplitude of density oscillations (i.e. 10% and above), nonlinear
effects and anharmonicity have a small effect on the interplay of the
nonleptonic and semileptonic processes in the bulk viscosity.Comment: 14 pages, 6 figures; v2: Appendix B is omitted, a few new discussions
added and some new references adde
- …