Key points are not available for this paper at this time.
The asymptotic fields in a canonically quantized gravitational field with higher derivatives are analyzed. A possible mechanism of the recovery of the physical S-matrix unitarity is discussed. The constraint ࢟µBµν + (β/α) gµνB = 0 due to the Bianchi identity on Rµν is treated by Dirac's method.
Kawasaki et al. (Mon,) studied this question.