170 research outputs found
Inhomogeneous phases in the Nambu-Jona-Lasino and quark-meson model
We discuss inhomogeneous ground states of the Nambu-Jona-Lasino (NJL) and
quark-meson (QM) model within mean-field approximation and their possible
existence in the respective phase diagrams. For this purpose we focus on lower
dimensional modulations and point out that known solutions in the 2+1 and 1+1
dimensional (chiral) Gross-Neveu (GN) model can be lifted to the to the 3+1
dimensional NJL model. This is worked out in detail for one-dimensional
modulations and numerical results for the phase diagrams are presented. Focus
is put on the critical point and on vanishing temperatures. As an interesting
result the first order transition line in the phase diagram of homogeneous
phases gets replaced by an inhomogeneous phase which is bordered by two second
order transition lines.Comment: 21 pages, 11 figure
On the unlocking of color and flavor in color-superconducting quark matter
The role of the strange quark mass for the phase structure of QCD at
non-vanishing densities is studied by employing a recently developed
self-consistent truncation scheme for the Dyson-Schwinger equations of the
quark propagators in Landau gauge. Hereby the medium modification of the
effective quark interaction by the polarization of gluons is implemented.
Taking into account this effect results in significantly smaller dynamical
quark masses at the Fermi surface. Due to this reduction the color-flavor
locked phase is always the preferred color-superconducting phase at zero
temperature and for a realistic strange quark mass.Comment: 14 pages, 8 figure
Neutrality of the color-flavor-locked phase in a Dyson-Schwinger approach
The role of neutrality constraints for the phase structure of QCD at
non-vanishing chemical potentials is studied within a self-consistent
truncation scheme for the Dyson-Schwinger equation of the quark propagator in
Landau gauge. We find the (approximate) color-flavor-locked phase to be
energetically preferred at all potentially relevant densities and for physical
values of the quark masses. We furthermore observe the impossibility to define
this phase by residual global symmetries and discuss the role of chemical
potentials.Comment: 10 pages, 4 figure
Black holes and non-relativistic quantum systems
We describe black holes in d+3 dimensions, whose thermodynamic properties
correspond to those of a scale invariant non-relativistic d+1 dimensional
quantum system with dynamical exponent z=2. The gravitational model involves a
massive abelian vector field and a scalar field, in addition to the metric. The
energy per particle in the dual theory is , exactly as in a
non-interacting Fermi gas, while the ratio of shear viscosity to entropy
density is .Comment: 8 pages; v2: discussion modifie
Quark spectral properties above Tc from Dyson-Schwinger equations
We report on an analysis of the quark spectral representation at finite
temperatures based on the quark propagator determined from its Dyson-Schwinger
equation in Landau gauge. In Euclidean space we achieve nice agreement with
recent results from quenched lattice QCD. We find different analytical
properties of the quark propagator below and above the deconfinement
transition. Using a variety of ansaetze for the spectral function we then
analyze the possible quasiparticle spectrum, in particular its quark mass and
momentum dependence in the high temperature phase. This analysis is completed
by an application of the Maximum Entropy Method, in principle allowing for any
positive semi-definite spectral function. Our results motivate a more direct
determination of the spectral function in the framework of Dyson-Schwinger
equations
Color-spin locking in a self-consistent Dyson-Schwinger approach
We investigate the color-spin locked (CSL) phase of spin-one color-
superconducting quark matter using a truncated Dyson-Schwinger equation for the
quark propagator in Landau gauge. Starting from the most general parity
conserving ansatz allowed by the CSL symmetry, the Dyson-Schwinger equation is
solved self-consistently and dispersion relations are discussed. We find that
chiral symmetry is spontaneously broken due to terms which have previously been
neglected. As a consequence, the excitation spectrum contains only gapped modes
even for massless quarks. Moreover, at moderate chemical potentials the
quasiparticle pairing gaps are several times larger than expected from
extrapolated weak-coupling results.Comment: 9 pages, 7 figure
Radiation of a circulating quark in strongly coupled N=4 super Yang-Mills theory
The energy density and angular distribution of power radiated by a quark
undergoing circular motion in strongly coupled supersymmetric
Yang-Mills (SYM) theory is computed using gauge/gravity duality. The results
are qualitatively similar to that of synchrotron radiation produced by an
electron in circular motion in classical electrodynamics: At large velocities
the quark emits radiation in a narrow beam along its velocity vector with a
characteristic opening angle and radial thickness
scaling like .Comment: 8 pages, 2 figures - Talk presented by D. Nickel at QCD@Work, June
20-23rd, 2010, Martina Franca, Ital
Extraction of Spectral Functions from Dyson-Schwinger Studies via the Maximum Entropy Method
It is shown how to apply the Maximum Entropy Method (MEM) to numerical
Dyson-Schwinger studies for the extraction of spectral functions of correlators
from their corresponding Euclidean propagators. Differences to the application
in lattice QCD are emphasized and, as an example, the spectral functions of
massless quarks in cold and dense matter are presented.Comment: 16 pages, 7 figure
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