60 research outputs found
Commutative limit of a renormalizable noncommutative model
Renormalizable models on Moyal space have been obtained by
modifying the commutative propagator. But these models have a divergent "naive"
commutative limit. We explain here how to obtain a coherent such commutative
limit for a recently proposed translation-invariant model. The mechanism relies
on the analysis of the uv/ir mixing in general Feynman graphs.Comment: 11 pages, 3 figures, minor misprints being correcte
Overview of the parametric representation of renormalizable non-commutative field theory
We review here the parametric representation of Feynman amplitudes of
renormalizable non-commutative quantum field models.Comment: 10 pages, 3 figures, to be published in "Journal of Physics:
Conference Series
Super-Group Field Cosmology
In this paper we construct a model for group field cosmology. The classical
equations of motion for the non-interactive part of this model generate the
Hamiltonian constraint of loop quantum gravity for a homogeneous isotropic
universe filled with a scalar matter field. The interactions represent topology
changing processes that occurs due to joining and splitting of universes. These
universes in the multiverse are assumed to obey both bosonic and fermionic
statistics, and so a supersymmetric multiverse is constructed using superspace
formalism. We also introduce gauge symmetry in this model. The supersymmetry
and gauge symmetry are introduced at the level of third quantized fields, and
not the second quantized ones. This is the first time that supersymmetry has
been discussed at the level of third quantized fields.Comment: 14 pages, 0 figures, accepted for publication in Class. Quant. Gra
EPRL/FK Group Field Theory
The purpose of this short note is to clarify the Group Field Theory vertex
and propagators corresponding to the EPRL/FK spin foam models and to detail the
subtraction of leading divergences of the model.Comment: 20 pages, 2 figure
On the Effective Action of Noncommutative Yang-Mills Theory
We compute here the Yang-Mills effective action on Moyal space by integrating
over the scalar fields in a noncommutative scalar field theory with harmonic
term, minimally coupled to an external gauge potential. We also explain the
special regularisation scheme chosen here and give some links to the Schwinger
parametric representation. Finally, we discuss the results obtained: a
noncommutative possibly renormalisable Yang-Mills theory.Comment: 19 pages, 6 figures. At the occasion of the "International Conference
on Noncommutative Geometry and Physics", April 2007, Orsay (France). To
appear in J. Phys. Conf. Se
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
Diamond deposition on modified silicon substrates: Making diamond atomic force microscopy tips for nanofriction experiments
Fine-crystalline diamond particles are grown on standard Si atomic force microscopy tips, using hot filament-assisted chemical vapor deposition. To optimize the conditions for diamond deposition, first a series of experiments is carried out using silicon substrates covered by point-topped pyramids as obtained by wet chemical etching. The apexes and the edges of the silicon pyramids provide favorable sites for diamond nucleation and growth. The investigation of the deposited polycrystallites is done by means of optical microscopy, scanning electron microscopy and micro-Raman spectroscopy. The resulting diamond-terminated tips are tested in ultra high vacuum using contact-mode atomic force microscope on a stepped surface of sapphire showing high stability, sharpness, and hardnes
Operator Spin Foam Models
The goal of this paper is to introduce a systematic approach to spin foams.
We define operator spin foams, that is foams labelled by group representations
and operators, as the main tool. An equivalence relation we impose in the set
of the operator spin foams allows to split the faces and the edges of the
foams. The consistency with that relation requires introduction of the
(familiar for the BF theory) face amplitude. The operator spin foam models are
defined quite generally. Imposing a maximal symmetry leads to a family we call
natural operator spin foam models. This symmetry, combined with demanding
consistency with splitting the edges, determines a complete characterization of
a general natural model. It can be obtained by applying arbitrary (quantum)
constraints on an arbitrary BF spin foam model. In particular, imposing
suitable constraints on Spin(4) BF spin foam model is exactly the way we tend
to view 4d quantum gravity, starting with the BC model and continuing with the
EPRL or FK models. That makes our framework directly applicable to those
models. Specifically, our operator spin foam framework can be translated into
the language of spin foams and partition functions. We discuss the examples: BF
spin foam model, the BC model, and the model obtained by application of our
framework to the EPRL intertwiners.Comment: 19 pages, 11 figures, RevTex4.
West Nile Virus Encephalitis and Myocarditis in Wolf and Dog
In the third season (2002) of the West Nile virus epidemic in the United States, two canids (wolf and dog) were diagnosed with West Nile virus encephalitis and myocarditis with similarities to known affected species (humans, horses, and birds). The West Nile virus infections were confirmed by immunohistochemistry and polymerase chain reaction
- …