Effective potential for a covariantly constant gauge field in curved spacetime

We discuss the influence of gravitational effects on the stabilization of the chromomagnetic vacuum. The one-loop effective potential for a covariantly constant SU(2) gauge field in S-2 x R(2) and T-2 x R(2) is calculated. The possibility of curvature-induced phase transitions between zero and nonzero chromomagnetic vacua is found-which is also confirmed through the calculation of the renormalization-group-improved effective potential on constant-curvature spaces with small curvature. Numerical evaluation indicates that for some curvatures the imaginary part of the effective potential disappears (gravitational stabilization of the chromomagnetic vacuum occurs).