On the Field Renormalization Constant for Unstable Particles

A recently proposed normalization condition for the imaginary part of the self-energy of an unstable particle is shown to lead to a closed expression for the field renormalization constant Z. In turn, the exact expression for Z is necessary, in some important cases, in order to avoid power-like infrared divergences in high orders of perturbation theory. In the same examples, the width plays the r\^ole of an infrared cutoff and, consequently, Z is not an analytic function of the coupling constant.Comment: 7 pages (Latex

The muon g-2 discrepancy: errors or new physics?

After a brief review of the muon g-2 status, we discuss hypothetical errors in the Standard Model prediction that could explain the present discrepancy with the experimental value. None of them looks likely. In particular, an hypothetical increase of the hadroproduction cross section in low-energy e^+e^- collisions could bridge the muon g-2 discrepancy, but is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 130 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.Comment: 4 pages. Invited talk at 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), June 16-21 2008, Seoul, Kore

MOLECULAR PLANT-MICROBIOTA INTERACTION FOR BIOCONTROL OF PLANT PATHOGENS

Il controllo delle fitopatie \ue8 un tema molto importante nell\u2019agricoltura moderna: da un lato si vede il bisogno di mantenere alto, ed anzi incrementare, il livello produttivo delle colture; dall\u2019altro vi \ue8 una forte spinta verso la riduzione di input in agricoltura per ottenere una maggiore sostenibilit\ue0 dei processi produttivi. In questo scenario, il controllo biologico, o biocontrollo, dei patogeni pu\uf2 essere un valido strumento per raggiungere entrambi gli obbiettivi. Nel presente lavoro di tesi \ue8 stata valutata la capacit\ue0 di 7 diversi ceppi batterici, precedentemente isolati da piante di melo e vite, di essere agenti di biocontrollo e di promozione della crescita. I diversi saggi condotti nell\u2019ambito di questo studio hanno incluso prove in vitro, in vivo, in planta, ed in silico per caratterizzare le potenzialit\ue0 di questi ceppi, ottenendo i risultati di seguito riassunti: capacit\ue0 di inibire la crescita miceliare di ascomycota e basidiomycota in vitro; capacit\ue0 di ridurre la colonizzazione da parte di Botrytis cinerea in vivo su bacche di pomodoro; capacit\ue0 di promuovere la crescita e di ridurre l\u2019incidenza di Pseudomonas syringae e Cymbidium Ringspot Virus su piante di peperone in planta; identificazione di tratti genetici noti e di possibile nuovo interesse per il biocontrollo dall\u2019analisi in silico dei genomi dei ceppi. In conclusione, questo studio non ha solo caratterizzato l\u2019effetto di 7 ceppi candidati agenti di biocontrollo, ma ha indagato sui loro meccanismi d\u2019azione, ponendo le basi per ulteriori studi atti a definire con maggior precisione i meccanismi molecolari alla base del biocontrollo al fine di identificare nuovi strumenti per un\u2019agricoltura moderna e sostenibile.The control of plant diseases is a very important topic in modern agriculture: on one hand, there is the necessity to maintain a high production level, and even to achieve higher production of crops; on the other, there is a strong drive towards the reduction of inputs in agriculture in order to achieve more sustainable productive processes. In this scenario, biological control, or biocontrol, of pathogens can be a helpful tool to achieve both objectives. In this thesis work the ability of 7 different bacterial strains, previously isolated from apple trees and grapevine plants, to act as biocontrol and plant-growth promoting agents was evaluated. Different assays were carried out in this study, including in vitro, in vivo, in planta, and in silico assays carried out to characterize the potential of these strains, achieving the results summarized as follows: ability to inhibit mycelial growth of ascomycota and basidiomycota in vitro: ability to reduce colonization by Botrytis cinerea in vivo on tomato berries: ability to promote growth and reduce the incidence of Pseudomonas syringae and Cymbidium Ringspot Virus on pepper plants during in planta assays; identification of known and possibly novel genetic traits for biocontrol from the in silico analysis of the genomes of the strains. In conclusion, this study has not only characterized the effect of 7 candidate biocontrol strains, but has investigated their mechanisms of action, paving the road for further studies aimed at defining more precisely the fine molecular mechanisms at the base of biocontrol and to identify new tools for a modern and sustainable agriculture

A New Renormalization Scheme of Fermion Fields in Electroweak Standard Model

This paper has been withdrawn by the author,due a immature idea.Comment: 6 page

Radiative Corrections to W and Quark Propagators in the Resonance Region

We discuss radiative corrections to W and quark propagators in the resonance region, |s-M^2| \lsim M*Gamma. We show that conventional mass renormalization, when applied to photonic or gluonic corrections, leads in next to leading order (NLO) to contributions proportional to [M*Gamma/(s-M^2)]^n, (n=1,2...), i.e. to a non-convergent series in the resonance region, a difficulty that affects all unstable particles coupled to massless quanta. A solution of this problem, based on the concepts of pole mass and width, is presented. It elucidates the issue of renormalization of amplitudes involving unstable particles and automatically circumvents the problem of apparent on-shell singularities. The roles of the Fried-Yennie gauge and the Pinch Technique prescription are discussed. Because of special properties of the photonic and gluonic contributions, and in contrast with the Z case, the gauge dependence of the conventional on-shell definition of mass is unbounded in NLO. The evaluations of the width in the conventional and pole formulations are compared and shown to agree in NLO but not beyond.Comment: 19 pages, 7 figures, LaTeX (uses epsfig). Slight rewording of the abstract and one of the sentences of the text. Minor misprints corrected. To appear in Phys. Rev.