1,233 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
On Non-Commutative U*(1) Gauge Models and Renormalizability
Based on our recent findings regarding (non-)renormalizability of
non-commutative U*(1) gauge theories [arxiv:0908.0467, arxiv:0908.1743] we
present the construction of a new type of model. By introducing a soft breaking
term in such a way that only the bilinear part of the action is modified, no
interaction between the gauge sector and auxiliary fields occurs. Demanding in
addition that the latter form BRST doublet structures, this leads to a
minimally altered non-commutative U*(1) gauge model featuring an IR damping
behavior. Moreover, the new breaking term is shown to provide the necessary
structure in order to absorb the inevitable quadratic IR divergences appearing
at one-loop level in theories of this kind. In the present paper we compute
Feynman rules, symmetries and results for the vacuum polarization together with
the one-loop renormalization of the gauge boson propagator and the three-point
functions.Comment: 20 pages, 4 figures; v2-v4: clarified several points, and minor
correction
Width of the QCD transition in a Polyakov-loop DSE model
We consider the pseudocritical temperatures for the chiral and deconfinement
transitions within a Polyakov-loop Dyson-Schwinger equation approach which
employs a nonlocal rank-2 separable model for the effective gluon propagator.
These pseudocritical temperatures differ by a factor of two when the quark and
gluon sectors are considered separately, but get synchronized and become
coincident when their coupling is switched on. The coupling of the
Polyakov-loop to the chiral quark dynamics narrows the temperature region of
the QCD transition in which chiral symmetry and deconfinement is established.
We investigate the effect of rescaling the parameter T_0 in the Polyakov-loop
potential on the QCD transition for both the logarithmic and polynomial forms
of the potential. While the critical temperatures vary in a similar way, the
width of the transition is stronger affected for the logarithmic potential. For
this potential the character of the transition changes from crossover to a
first order one when T_0 < 210 MeV, but it remains crossover in the whole range
of relevant T_0 values for the polynomial form.Comment: 10 pages, 6 figures, results for polynomial form of Polyakov-loop
potential included, references added, final version to appear in Phys. Rev.
Heavy flavor kinetics at the hadronization transition
We investigate the in-medium modification of the charmonium breakup processes
due to the Mott effect for light (pi, rho) and open-charm (D, D*)
quark-antiquark bound states at the chiral/deconfinement phase transition. The
Mott effect for the D-mesons effectively reduces the threshold for charmonium
breakup cross sections, which is suggested as an explanation of the anomalous
J/psi suppression phenomenon in the NA50 experiment. Further implications of
finite-temperature mesonic correlations for the hadronization of heavy flavors
in heavy-ion collisions are discussed.Comment: 4 pages, 2 figures, Contribution to SQM2001 Conference, submitted to
J. Phys.
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
On the Renormalizability of Noncommutative U(1) Gauge Theory - an Algebraic Approach
We investigate the quantum effects of the nonlocal gauge invariant operator
in the
noncommutative U(1) action and its consequences to the infrared sector of the
theory. Nonlocal operators of such kind were proposed to solve the infrared
problem of the noncommutative gauge theories evading the questions on the
explicit breaking of the Lorentz invariance. More recently, a first step in the
localization of this operator was accomplished by means of the introduction of
an extra tensorial matter field, and the first loop analysis was carried out
. We will complete this localization
avoiding the introduction of new degrees of freedom beyond those of the
original action by using only BRST doublets. This will allow us to make a
complete BRST algebraic study of the renormalizability of the theory, following
Zwanziger's method of localization of nonlocal operators in QFT.Comment: standard Latex no figures, version2 accepted in J. Phys A: Math Theo
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
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