1,328 research outputs found
A New Approach to Non-Commutative U(N) Gauge Fields
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction
1-2-3-flavor color superconductivity in compact stars
We suggest a scenario where the three light quark flavors are sequentially
deconfined under increasing pressure in cold asymmetric nuclear matter, e.g.,
as in neutron stars. The basis for our analysis is a chiral quark matter model
of Nambu--Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single
flavor (CSL) and spin-0 two/three flavor (2SC/CFL) channels, and a
Dirac-Brueckner Hartree-Fock (DBHF) approach in the nuclear matter sector. We
find that nucleon dissociation sets in at about the saturation density, n_0,
when the down-quark Fermi sea is populated (d-quark dripline) due to the flavor
asymmetry imposed by beta-equilibrium and charge neutrality. At about 3n_0
u-quarks appear forming a two-flavor color superconducting (2SC) phase, while
the s-quark Fermi sea is populated only at still higher baryon density. The
hybrid star sequence has a maximum mass of 2.1 M_sun. Two- and three-flavor
quark matter phases are found only in gravitationally unstable hybrid star
solutions.Comment: 4 pages, 2 figures, to appear in the proceedings of Quark Matter
2008: 20th International Conference on Ultra-Relativistic Nucleus Nucleus
Collisions (QM 2008), Jaipur, India, 4-10 Feb 200
How strange are compact star interiors ?
We discuss a Nambu--Jona-Lasinio (NJL) type quantum field theoretical
approach to the quark matter equation of state with color superconductivity and
construct hybrid star models on this basis. It has recently been demonstrated
that with increasing baryon density, the different quark flavors may occur
sequentially, starting with down-quarks only, before the second light quark
flavor and at highest densities also the strange quark flavor appears. We find
that color superconducting phases are favorable over non-superconducting ones
which entails consequences for thermodynamic and transport properties of hybrid
star matter. In particular, for NJL-type models no strange quark matter phases
can occur in compact star interiors due to mechanical instability against
gravitational collapse, unless a sufficiently strong flavor mixing as provided
by the Kobayashi-Maskawa-'t Hooft determinant interaction is present in the
model. We discuss observational data on mass-radius relationships of compact
stars which can put constraints on the properties of dense matter equation of
state.Comment: 7 pages, 2 figures, to appear in the Proceedings of the International
Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200
Hybrid Stars in an SU(3) Parity Doublet Model
We apply an extended version of the SU(3) parity model, containing quark
degrees of freedom, to study neutron stars. The model successfully reproduces
the main thermodynamic features of QCD which allows us to describe the
composition of dense matter. Chiral symmetry restoration is realized inside the
star and the chiral partners of the baryons appear, their masses becoming
degenerate. Furthermore, quark degrees of freedom appear in a transition to a
deconfined state. Performing an investigation of the macroscopic properties of
neutron stars, we show that observational constraints, like mass and thermal
evolution, are satisfied and new predictions can be made
Heat kernel expansion and induced action for matrix models
In this proceeding note, I review some recent results concerning the quantum
effective action of certain matrix models, i.e. the supersymmetric IKKT model,
in the context of emergent gravity. The absence of pathological UV/IR mixing is
discussed, as well as dynamical SUSY breaking and some relations with string
theory and supergravity.Comment: 11 pages, 1 figure; talk given at the 7th International Conference on
Quantum Theory and Symmetries, August 7-13, 2011, Prague/Czech Republi
Schwarzschild Geometry Emerging from Matrix Models
We demonstrate how various geometries can emerge from Yang-Mills type matrix
models with branes, and consider the examples of Schwarzschild and
Reissner-Nordstroem geometry. We provide an explicit embedding of these branes
in R^{2,5} and R^{4,6}, as well as an appropriate Poisson resp. symplectic
structure which determines the non-commutativity of space-time. The embedding
is asymptotically flat with asymptotically constant \theta^{\mu\nu} for large
r, and therefore suitable for a generalization to many-body configurations.
This is an illustration of our previous work arXiv:1003.4132, where we have
shown how the Einstein-Hilbert action can be realized within such matrix
models.Comment: 21 pages, 1 figur
Quark exchange model for charmonium dissociation in hot hadronic matter
A diagrammatic approach to quark exchange processes in meson-meson scattering
is applied to the case of inelastic reactions of the type
(Q\barQ)+(q\barq)\rightarrow (Q\barq) + (q\barQ), where and refer to
heavy and light quarks, respectively. This string-flip process is discussed as
a microscopic mechanism for charmonium dissociation (absorption) in hadronic
matter. The cross section for the reaction is
calculated using a potential model, which is fitted to the meson mass spectrum.
The temperature dependence of the relaxation time for the \J/Psi distribution
in a homogeneous thermal pion gas is obtained. The use of charmonium for the
diagnostics of the state of hot hadronic matter produced in ultrarelativistic
nucleus-nucleus collisions is discussed.Comment: 24 pages, 3 tables, 7 figure
Phase diagrams in nonlocal PNJL models constrained by Lattice QCD results
Based on lattice QCD-adjusted SU(2) nonlocal Polyakov--Nambu--Jona-Lasinio
(PNJL) models, we investigate how the location of the critical endpoint in the
QCD phase diagram depends on the strenght of the vector meson coupling, as well
as the Polyakov-loop (PL) potential and the form factors of the covariant
model. The latter are constrained by lattice QCD data for the quark propagator.
The strength of the vector coupling is adjusted such as to reproduce the slope
of the pseudocritical temperature for the chiral phase transition at low
chemical potential extracted recently from lattice QCD simulations. Our study
supports the existence of a critical endpoint in the QCD phase diagram albeit
the constraint for the vector coupling shifts its location to lower
temperatures and higher baryochemical potentials than in the case without it.Comment: 23 pages, 10 figures. Version accepted in Phys. Part. Nucl. Lett. (to
appear), references adde
Symmetry energy of dilute warm nuclear matter
The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. New data from heavy-ion collisions can be used to extract the free
symmetry energy and the internal symmetry energy at subsaturation densities and
temperatures below 10 MeV. Conventional theoretical calculations of the
symmetry energy based on mean-field approaches fail to give the correct
low-temperature, low-density limit that is governed by correlations, in
particular by the appearance of bound states. A recently developed quantum
statistical (QS) approach that takes the formation of clusters into account
predicts symmetry energies that are in very good agreement with the
experimental data. A consistent description of the symmetry energy is given
that joins the correct low-density limit with quasiparticle approaches valid
near the saturation density.Comment: 4 pages, 2 figures, 1 tabl
Scalar correlations in a quark plasma and low mass dilepton production
We investigate possible consequences of resonant scalar interactions for
dilepton production from a quark plasma at the chiral phase transition. It is
found that this production mechanism is strongly suppressed compared to the
Born process and has no significance for present experiments.Comment: 7 pages revtex, 2 ps figure
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