Antonio Vairo

Quarkonium spectroscopy and perturbative QCD: a new perspective

We study the energy spectrum of bottomonium in perturbative QCD, taking alpha_s(Mz)=0.1181 +/- 0.0020 as input and fixing m_b^{MSbar}(m_b^{MSbar}) on the Upsilon(1S) mass. Contrary to wide beliefs, perturbative QCD reproduces reasonably well the gross structure of the spectrum as long as the coupling constant remains smaller than one. We perform a detailed analysis and discuss the size of non-perturbative effects. A new qualitative picture on the structure of the bottomonium spectrum is provided. The lowest-lying (c,cbar) and (b,cbar) states are also examined.

Quarkonium spectroscopy and perturbative QCD: Massive quark loop effects

We study the spectra of the bottomonium and Bc states within perturbative QCD up to order � 4 . The O(�QCD) renormalon cancellation between the static potential and the pole mass is performed in the -expansion scheme. We extend our previous analysis by including the (dominant) effects of non-zero charm-quark mass in loops up to the next-to-leading non-vanishing order 3 . We fix the b-quark MS mass mb ≡ m MS (m MS ) on �(1S) and compute the higher levels. The effect of the charm mass decreases mb by about 11 MeV and increases the n = 2 and n = 3 levels by about 70–100 MeV and 240–280 MeV, respectively. We provide an extensive quantitative analysis. The size of non-perturbative and higher order contributions is discussed by comparing the obtained predictions with the experimental data. An agreement of the perturbative predictions and the experimental data depends crucially on the precise value (inside � �

A lattice determination of QCD field strength correlators

Abstract We study field strength correlators in presence of a static quark-antiquark pair by use of lattice methods. The lattice data have been acquired recently in the context of a determination of relativistic corrections to the static interquark potential. We extract independent estimates of the form factors of two point correlation functions and investigate the effect of higher order correlators. Our results confirm the dominance of the two point correlators in the regions of intermediate and large quark separations, and are compatible with correlation length values obtained from different approaches.

Field strength correlators and dual effective dynamics in QCD

We establish a relation between the two-point field strength correlator in QCD and the dual field propagator of an effective dual Abelian Higgs model describing the infrared behaviour of QCD. We find an analytic approximation to the dual field propagator without sources and in presence of quark sources. In the latter situation we also obtain an expression for the static

Poincaré invariance constraints on non-relativistic effective field theories

q bar{q}

The qq semirelativistic interaction in the Wilson loop approach

potential. Our derivation sheds some light on the dominance and phenomenological relevance of the two-point field strength correlator.

The Barbieri-Remiddi Solution of the Bound-State Problem in QED

We discuss Poincare invariance in the context of non-relativistic effective field theories of QCD. We show, in the cases of the HQET and pNRQCD, that the algebra of the generators of the Poincare transformations imposes precise constraints on the form of the Lagrangian. In the case of the HQET they are the relations formerly obtained by reparametrization invariance.

The non-perturbative QCD potential

The complete qq semirelativistic interaction is obtained as a guage-invariant function of the Wilson loop and its functional derivatives. The approach is suitable for analytic evaluations as well as for lattice calculations. Here we consider three different models for the Wilson loop non-perturbative behaviour and discuss the related semirelativistic dynamics.

Non-perturbative dynamics of the heavy-light quark system

We derive the so-called Barbieri-Remiddi solution of the Bethe-Salpeter equation in QED in its general form and discuss its application to the bound-state energy spectrum.

The QCD potential at O (1 /

Abstract The potential between heavy quarks can be rigorously defined in a QCD effective field theories framework. I discuss the general situation when the coupling constant may not be considered small and provide an explicit expression for the potential valid up to order 1/m2. Spin dependent and spin independent terms are expressed in terms of Wilson loops, completing (and correcting) an ideal journey started twenty years ago with the classical work of Eichten and Feinberg.