INDIAN JOURNAL OF PURE & APPLIED MATHEMATICS, cilt.29, sa.10, ss.1029-1048, 1998 (SCI-Expanded)
We calculate the vacuum expectation value of the stress-energy tensor for a scalar particle in the background metric of different types of spherical impulsive, spherical shock and plane impulsive gravitational waves. We get non-zero vaccum fluctuations only if we use the spherical impulsive wave as the background. We take a detour in de Sitter space for regularizing our result both in the ultraviolet and the infrared regions.