  We compute, within the Schwinger-boson scheme, the Gaussian-fluctuation
corrections to the order-parameter stiffness of two frustrated quantum spin
systems: the triangular-lattice Heisenberg antiferromagnet and the J1-J2 model
on the square lattice. For the triangular-lattice Heisenberg antiferromagnet we
found that the corrections weaken the stiffness, but the ground state of the
system remains ordered in the classical 120 spiral pattern. In the case of the
J1-J2 model, with increasing frustration the stiffness is reduced until it
vanishes, leaving a small window 0.53 < J2/J1 < 0.64 where the system has no
long-range magnetic order. In addition, we discuss several methodological
questions related to the Schwinger-boson approach. In particular, we show that
the consideration of finite clusters which require twisted boundary conditions
to fit the infinite-lattice magnetic order avoids the use of ad hoc factors to
correct the Schwinger-boson predictions.
