TITLE: Hadronic vacuum polarization in low energy physics

   Department of Theoretical Physics, 
   National Institute for Physics and Nuclear Engineering,
   Bucharest, POB MG-6, 76900, Romania
   e-mail: caprini@theory.nipne.ro

ABSTRACT:

The recent tests of the Standard Model (SM) and of possible new physics 
deviations from it depend in a crucial way of the ability of making precise 
predictions at low energies. A fundamental quantity relevant in the recent tests of 
SM is the hadronic polarization dressing the photon. This quantity can not be calculated completely in perturbative QCD and is very sensitive to nonperturbative contributions.
We discuss the relevance of the hadronic vacuum polarization for the value of the 
muon g-2 measured recently with very high precision at Brookhaven, and prove in
particular the equivalence of two alternative methods of including the hadronic loops beyond the leading order. 

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