  We demonstrate, in the context of a scalar version of the chiral effective
field theory, that the multi-sea quark contribution to the nucleon is
significant and highly non-trivial in sharp contrast to the prediction of
perturbation theory. The non-perturbative calculation is performed in the Fock
sector dependent renormalization scheme on the light front, in which the
non-perturbative renormalization is incorporated. The calculation suggests that
a fully non-perturbative calculation of the chiral EFT is needed to obtain a
robust result to be compared with the recent experimental measurement of flavor
asymmetry in the proton.
