Renormalization group equations for effective field theories

We derive the renormalization group equations for a generic nonrenormalizable theory. We show that the equations allow one to derive the structure of the leading divergences at any loop order in terms of one-loop diagrams only. In chiral perturbation theory, e.g., this means that one can obtain the series of leading chiral logs by calculating only one loop diagrams. We discuss also the renormalization group equations for the subleading divergences, and the crucial role of counterterms that vanish at the equations of motion. Finally, we show that the renormalization group equations obtained here apply equally well also to renormalizable theories.Comment: 40 pages, 4 figures, plain Late

Rigid invariance as derived from BRS invariance: The abelian Higgs model

Consequences of a symmetry, e.g.\ relations amongst Green functions, are renormalization scheme independently expressed in terms of a rigid Ward identity. The corresponding local version yields information on the respective current. In the case of spontaneous breakdown one has to define the theory via the BRS invariance and thus to construct rigid and current Ward identity non-trivially in accordance with it. We performed this construction to all orders of perturbation theory in the abelian Higgs model as a prelude to the standard model. A technical tool of interest in itself is the use of a doublet of external scalar ``background'' fields. The Callan-Symanzik equation has an interesting form and follows easily once the rigid invariance is established.Comment: 33 pages, Plain Te

Boson--fermion bound states in two dimensional QCD

We derive the boson--fermion bound state equation in a two dimensional gauge theory in the large--\nc limit. We analyze the properties of this equation and in particular, find that the mass trajectory is linear with respect to the bound state level for the higher mass states.Comment: 5pp, 2 figs (as a separate file), TIT/HEP-23

Vortex Solutions in Two-Higgs-Doublet Systems

We analyze the existence of string-like defects in a two-Higgs-doublet system having $SU(2) \times U(1)_Y \times U(1)_{Y^{\prime}}$ as gauge group. We are able to show that, when certain relations among the parameters hold, these configurations satisfy a set of first order differential equations (Bogomol'nyi equations) and their energy is proportional to their topological charge.}Comment: 9 page

A screening mechanism for extra W and Z gauge bosons

We generalize a previous construction of a fermiophobic model to the case of more than one extra $W$ and $Z$ gauge bosons. We focus in particular on the existence of screening configurations and their implication on the gauge boson mass spectrum. One of these configurations allows for the existence of a set of relatively light new gauge bosons, without violation of the quite restrictive bounds coming from the $\rho_{\rm NC}$ parameter. The links with Bess and degenerate Bess models are also discussed. Also the signal given here by this more traditional gauge extension of the SM could help to disentangle it from the towers of Kaluza-Klein states over $W$ and $Z$ gauge bosons in extra dimensions.Comment: 23 pages, 1 figure, extended discussion on precision tests. To appear in International Journal of Modern Physics

Phytoalexines et réactions de défense de la tomate aux infections par PHYTOPHTHORA PARASITICA et VERTICILLIUM ALBO-ATRUM

Deux cultivars de tomates de phénotype Saint-Pierre, isogéniques pour la résistance à la verticilliose et différents par celle au mildiou (et à PHYTOPHTHORA PARASITICA Dast.), sont inoculés par P. PARASITICA et par VERTICILLIUM ALBO-ATRUM Reinke et Berth. Aux réactions de défense correspond l'accumulation, dans les tissus, de sesquiterpènes, de composés phénoliques, de tomatine et de dérivés oxygénés de linoléate de méthyle. Les synthèses de ces substances chez l'hôte sont modulées selon les cultivars et les parasites confrontés. Les études d'inhibition in vitro de P. PARASITICA révèlent une importante synergie entre des diénols d'une part, et des produits phénoliques et la tomatine d'autre part

Inflammatory Profile and Osteogenic Potential of Fracture Haematoma in Humans

Fracture haematoma forms immediately after fracture and is considered essential for the bone healing process. Its molecular composition has been briefly investigated with our current understanding being based on animal studies. This study aims to analyse the inflammatory cytokine content of fracture haematoma in humans and determine its effect on osteoprogenitor cells. Twenty-three patients were recruited following informed consent. Peripheral blood, fracture haematoma and bone were collected. A Luminex assay on the levels of 34 cytokines was performed and autologous peripheral blood samples served as control. Mesenchymal Stem Cells (MSCs) were isolated following collagenase digestion and functional assays were performed. Gene expression analysis of 84 key osteogenic molecules was performed. Thirty-three inflammatory cytokines were found to be significantly raised in fracture haematoma when compared to peripheral serum (p < 0.05). Amongst the most raised molecules were IL-8, IL-11 and MMP1, -2 and -3. Fracture haematoma did not significantly affect MSC proliferation, but ALP activity and calcium deposition were significantly increased in the MSCs undergoing osteogenic differentiation. Medium supplementations with fracture haematoma resulted in a statistically significant upregulation of osteogenic genes including the EGF, FGF2 and VEGFA. This seems to be the pathway involved in the osteogenic effect of fracture haematoma on bone cells. In conclusion, fracture haematoma is found to be a medium rich in inflammatory and immunomodulatory mediators. At the same time, it contains high levels of anti-inflammatory molecules, regulates osteoclastogenesis, induces angiogenesis and the production of the extracellular matrix. It appears that fracture haematoma does not affect osteoprogenitor cells proliferation as previously thought, but induces an osteogenic phenotype

Supergrassmannian and large N limit of quantum field theory with bosons and fermions

We study a large N_{c} limit of a two-dimensional Yang-Mills theory coupled to bosons and fermions in the fundamental representation. Extending an approach due to Rajeev we show that the limiting theory can be described as a classical Hamiltonian system whose phase space is an infinite-dimensional supergrassmannian. The linear approximation to the equations of motion and the constraint yields the 't Hooft equations for the mesonic spectrum. Two other approximation schemes to the exact equations are discussed.Comment: 24 pages, Latex; v.3 appendix added, typos corrected, to appear in JM

Off-Forward Parton Distributions in 1+1 Dimensional QCD

We use two-dimensional QCD as a toy laboratory to study off-forward parton distributions (OFPDs) in a covariant field theory. Exact expressions (to leading order in $1/N_C$) are presented for OFPDs in this model and are evaluated for some specific numerical examples. Special emphasis is put on comparing the $x>\zeta$ and $x<\zeta$ regimes as well as on analyzing the implications for the light-cone description of form factors.Comment: Revtex, 6 pages, 4 figure