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The p(p,e^+ \nu_e)^2H reaction rate is an essential ingredient fortheoretical computations of stellar models. In the past several values of thecorresponding S-factor have been made available by different authors. Promptedby a recent evaluation of S(E), we analysed the effect of the adoption ofdifferent proton-proton reaction rates on stellar models, focusing, inparticular, on the age of mid and old stellar clusters (1-12 Gyr) and onstandard solar model predictions. By comparing different widely adopted p(p,e^+\nu_e)^2H reaction rates, we found a maximum difference in the temperatureregimes typical of main sequence hydrogen-burning stars (5x10^6 - 3x10^7 K) ofabout 3%. Such a variation translates into a change of cluster agedetermination lower than 1%. A slightly larger effect is observed in thepredicted solar neutrino fluxes with a maximum difference, in the worst case,of about 8%. Finally we also notice that the uncertainty evaluation of thepresent proton-proton rate is at the level of few \permil, thus the p(p,e^+\nu_e)^2H reaction rate does not constitute anymore a significant uncertaintysource in stellar models.

Astrophysical implications of the proton-proton cross section updates