1-LOOP FORM-FACTORS IN THE EFFECTIVE ACTION AND PRODUCTION OF COHERENT GRAVITONS FROM THE VACUUM

We present the solution of the problem of 1/square, square --> 0 asymp totic terms discovered in the 1-loop form factors of the gravitational effective action. Owing to certain constraints among their coefficien ts, which we establish, these terms cancel in the vacuum stress tenser and do not violate the asymptotic flatness of the expectation value o f the metric. They reappear, however, in the Riemann tenser of this me tric and represent a new effect: a radiation of gravitational waves in duced by the vacuum stress. This coherent radiation caused by the back reaction adds to the non-coherent radiation caused by the pair creatio n in the case where the initial state provides the vacuum stress tense r with a quadrupole moment.