Av. Balakrishnan et R. Triggiani, LACK OF GENERATION OF STRONGLY CONTINUOUS SEMIGROUPS BY THE DAMPED WAVE OPERATOR ON H X H (OR - THE LITTLE ENGINE THAT COULDNT), Applied mathematics letters, 6(6), 1993, pp. 33-37
We show that (in the unbounded case) the wave operator, or more genera
lly, a wave operator with damping strictly less than the basic operato
r does not generate a strongly continuous semigroup on the product spa
ce H x H, contrary to a common belief.