  Recently a long ranged superconductor/ferromagnet (S/F) proximity effect has
been reported in Co crystalline nanowires [1, Nature, 6 389 (2010)]. Since the
authors of [1] take care to avoid the existence of magnetic domains, the
triplet character of the long ranged proximity effect is improbable. Here we
demonstrate that in the one-dimensional ballistic regime the standard singlet
S/F proximity effect becomes long ranged. We provide an exact solution for the
decay of the superconducting correlations near critical temperature ($T_{c}$)
and for arbitrary impurities concentration. In particular we find a specific
regime, between the diffusive and ballistic ones, where the decay length is
simply the electronic mean-free path. Finally possible experiments which could
permit to elucidate the nature of the observed long ranged proximity effect in
Co nanowires are discussed.
