Commutative limit of a renormalizable noncommutative model

Renormalizable $\phi^{\star 4}_4$ 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

Parametric representation of a translation-invariant renormalizable noncommutative model

We construct here the parametric representation of a translation-invariant renormalizable scalar model on the noncommutative Moyal space of even dimension $D$. This representation of the Feynman amplitudes is based on some integral form of the noncommutative propagator. All types of graphs (planar and non-planar) are analyzed. The r\^ole played by noncommutativity is explicitly shown. This parametric representation established allows to calculate the power counting of the model. Furthermore, the space dimension $D$ is just a parameter in the formulas obtained. This paves the road for the dimensional regularization of this noncommutative model.Comment: 20 pages, 11 figures; the power counting dependence on the graph genus has been explicitly found; several misprints have been corrected; version accepted for publication to J. Phys. A: Math. Theo

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

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

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

Unexpected Features of Supersymmetry with Central Charges

It is shown that N=2 supersymmetric theories with central charges present some hidden quartic symmetry. This enables us to construct representations of the quartic structure induced by superalgebra representations.Comment: 14 pages, more details have been given, to appear in J. Phys.

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

New insights into the metabolic-bone crosstalk in active acromegaly

Introduction: Body composition (BC) and adipokines share bone active properties and display an altered profile in acromegaly. The fibroblast growth factor 23 (FGF23)/α-Klotho system, also involved in bone metabolism, is upregulated in growth hormone (GH) excess states. Hence, we aimed to investigate their impact on bone in active acromegaly, compared to controls. Material and methods: BC, bone mineral density (BMD) (via dual X-ray absorptiometry), serum adipokines (leptin, adiponectin, resistin), parathyroid hormone (PTH), FGF23, α-Klotho, and osteocalcin were assessed in a cross-sectional study enrolling 35 patients with active acromegaly (Acro), compared to 35 sex, age, and body mass index (BMI) one-to-one matched healthy controls (CTL). Results: The Acro group had higher bone density scores (p < 0.05), lower visceral fat depots (p = 0.011), and lower serum leptin (p < 0.001) but elevated adiponectin (p < 0.001) and resistin (p = 0.001) concentrations when compared to the CTL group. α-Klotho was not related to the GH/IGF1 axis in the Acro group. Resistin was higher in both diabetic and non-diabetic Acro compared to CTL (p < 0.05). Age and BC were the main independent BMD predictors in regression analysis in both groups, while IGF1 was a positive predictor of osteocalcin levels in the Acro (β = 0.48, p = 0.006). The correlations between adipokines, the FGF23/α-Klotho system, and bone parameters, respectively, were lost after adjusting for age and BC. Conclusions: Age and BC were the main independent BMD predictors in the acromegalic patients with active disease, while IGF1 was independently associated with serum osteocalcin concentrations. The role of α-Klotho in evaluating acromegaly and the associated osteopathy in the long-term appears to be limited. Our study is among the first to report significant serum resistin changes in patients with active acromegaly, opening new insights in the GH-mediated insulin resistance. The GH-resistin relationship merits further investigations

Translation-invariant models for non-commutative gauge fields

Motivated by the recent construction of a translation-invariant renormalizable non-commutative model for a scalar field (see arXiv:0802.0791 [math-ph]), we introduce models for non-commutative U(1) gauge fields along the same lines. More precisely, we include some extra terms into the action with the aim of getting rid of the UV/IR mixing.Comment: 9 page