13,006 research outputs found
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
QCD at Finite Density and Color Superconductivity
Brief review of current status of the field.Comment: Invited talk at Lattice 99, Pisa, July 1999. 5 pages, 7 fig
Phases of QCD at High Baryon Density
We review recent work on the phase structure of QCD at very high baryon
density. We introduce the phenomenon of color superconductivity and discuss how
the quark masses and chemical potentials determine the structure of the
superfluid quark phase. We comment on the possibility of kaon condensation at
very high baryon density and study the competition between superfluid, density
wave, and chiral crystal phases at intermediate density.Comment: 15 pages. To appear in the proceedings of the ECT Workshop on Neutron
Star Interiors, Trento, Italy, June 200
Instanton Effects in QCD at High Baryon Density
We study instanton effects in QCD at very high baryon density. In this regime
instantons are suppressed by a large power of , where
is the QCD scale parameter and is the baryon chemical
potential. Instantons are nevertheless important because they contribute to
several physical observables that vanish to all orders in perturbative QCD. We
study, in particular, the chiral condensate and its contribution to the masses of Goldstone bosons in the CFL phase of QCD
with flavors. We find that at densities , where
is the density of nuclear matter, the result is dominated by large
instantons and subject to considerable uncertainties. We suggest that these
uncertainties can be addressed using lattice calculations of the instanton
density and the pseudoscalar diquark mass in QCD with two colors. We study the
topological susceptibility and Witten-Veneziano type mass relations in both
and QCD.Comment: 27 pages, 8 figures, minor revision
Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling Microscopy
The low-energy electronic properties of one-dimensional nanowires formed by
Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the
millivolt-regime. The chain structure exhibits various dimerized elements at
high tunneling bias, indicative of a substrate bonding origin rather than a
charge density wave. Unexpectedly, this dimerization becomes vanishingly small
when imaging energy windows close to the Fermi level with adequately low
tunneling currents. Evenly spaced nanowire atoms emerge which are found to
represent conduction states. Implications for the metallicity of the chains are
discussed.Comment: 4 pages, 4 figure
On Color Superconductivity in External Magnetic Field
We study color superconductivity in external magnetic field. We discuss the
reason why the mixing angles in color-flavor locked (CFL) and two-flavor
superconductivity (2SC) phases are different despite the fact that the CFL gap
goes to the 2SC gap for . Although flavor symmetry is
explicitly broken in external magnetic field, we show that all values of gaps
in their coset spaces of possible solutions in the CFL phase are equivalent in
external magnetic field.Comment: 12 pages, LaTe
Superconductivity from perturbative one-gluon exchange in high density quark matter
We study color superconductivity in QCD at asymptotically large chemical
potential. In this limit, pairing is dominated by perturbative one-gluon
exchange. We derive the Eliashberg equation for the pairing gap and solve this
equation numerically. Taking into account both magnetic and electric gluon
exchanges, we find with ,
verifying a recent result by Son. For chemical potentials that are of physical
interest, GeV, the calculation ceases to be reliable quantitatively,
but our results suggest that the gap can be as large as 100 MeV.Comment: 19 pages, 6 figures. I accidentally replaced the paper with an
outdated version. This version has typos corrected and will appear in PR
Debye screening and Meissner effect in a three-flavor color superconductor
I compute the gluon self-energy in a color superconductor with three flavors
of massless quarks, where condensation of Cooper pairs breaks the color and
flavor SU(3)_c x U(3)_V x U(3)_A symmetry of QCD to the diagonal subgroup
SU(3)_{c+V}. At zero temperature, all eight electric gluons obtain a Debye
screening mass, and all eight magnetic gluons a Meissner mass. The Debye as
well as the Meissner masses are found to be equal for the different gluon
colors. These masses determine the coefficients of the kinetic terms in the
effective theory for the low-energy degrees of freedom. Their values agree with
those obtained by Son and Stephanov.Comment: 10 pages, 1 figure (eps
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