Meson-loop contributions in the quark model

We present a review of some recent results obtained in the unquenched quark model for baryons. The effects of sea quarks are taken into account in an explicit form via a QCD-inspired creation mechanism of the quark-antiquark pairs. In this approach, the contribution of the quark-antiquark pairs can be studied for any inital baryon and for any flavor of the q pairs (uū, d and s). It is shown that, whereas the inclusion of q pairs (or meson loops) does not affect the baryon magnetic moments, it immediately leads to an excess of over ū in the proton and introduces a sizeable contribution of orbital angular momentum to the spin of the proton. The contribution of s pairs to the magnetic moment and the radius of the proton is found to be small, in agreement with the latest experimental results and recent lattice calculations.