  We consider a simple cavity optomechanics and study the ground-state cooling
of mechanical resonator in the quantum regime. Using the effective master
equations in the linear regime, the equations of motion can be obtained for the
second order moments. The steady state solutions are derived in the case where
the antiresonant terms are ignored. The final mean value of phonon number is
compared to the case where the antiresonant terms are included. We find that
the ground-state cooling in the last case is improved. Indeed, the inclusion of
the antiresonant terms makes the system able to generate a squeezed field,
which is required for enhancing cooling. The variances of the resultant field
are presented. Analytic calculations are presented in some appropriate regimes.
Then our analytic predictions are confirmed with numerical calculations.
