We study the two-meson virtual cloud contribution to the self-energy of the
SU(3) antidecuplet, to which the Theta+ pentaquark is assumed to belong. This
is motivated by the large branching ratio of the N(1710) decay into two pions
and one nucleon. We derive effective Lagrangians that describe the N(1710)
decay into N-pi-pi with two pions in s or p wave. We obtain increased binding
for all members of the antidecuplet and a contribution to the mass splitting
between states with different strangeness which is at least 20 % of the
empirical one. We also provide predictions for three-body decays of the
pentaquark antidecuplet.Comment: 13 pages, To appear in Phys. Rev.
