Temperature dependence of three-gluon condensates in the instanton medium

The temperature dependence of three-gluon condensates in a disordered instanton medium is investigated beyond the low-temperature approximation in the cases of SU_C(2) and SU_C(3) colour groups. In considering the two-body classical interaction between instantons, the interference effects, i.e. the contributions to the gluon condensates from the overlap of two different instantons in the medium, are taken into account. The interference parts of the condensates are found to be quite small with respect to the corresponding non-interference ones. With a standard value for the QCD scale parameter, the three-gluon condensate at zero temperature is determined to be coincident with the phenomenological estimate without the introduction of an infrared cutoff for the instanton size. The resultant three-gluon condensates at finite T decrease as temperature increases. They are essentially constants when the temperature is below about 110 MeV, and change significantly within the temperature range 110-220 MeV for the case of SU_C(3). A limit temperature for the validity of the low-temperature expansion turned out to be about 80 MeV. When T>or=2.5 Lambda _MS, the three-gluon condensates, if they exist, should be negligible.