Asymptotic giant branch predictions: Theoretical uncertainties

In this paper we investigate the level of agreement between observations an d "new" Asymptotic Giant Branch (AGB) models, as produced by updating the p hysical inputs adopted in previous stellar computations. One finds that the new physics increases the predicted luminosity of Horizontal Branch (HB) a nd AGB stellar structures by a similar amount, keeping unchanged the predic tions about the difference in luminosity between these two evolutionary pha ses. The best fit of selected globular clusters appears rather satisfactory , disclosing the relevance of the assumption on the mass of the Red Giant B ranch (RGB) progenitor in assessing the distance modulus of moderately meta l rich clusters. The still existing uncertainties related either to the inp ut physics or to the efficiency of some macroscopic mechanisms, like convec tion or microscopic diffusion, are critically discussed, ruling out the occ urrence of the so called "breathing pulses" during the central He exhaustio n, in agreement with earlier suggestions.