Local and global smoothing effects for some linear hyperbolic equations   with a strong dissipation
  We consider an abstract second order linear equation with a strong dissipation, namely a friction term which depends on a power of the "elastic" operator.   In the homogeneous case, we investigate the phase spaces in which the initial value problem gives rise to a semigroup, and the further regularity of solutions. In the non-homogeneous case, we study how the regularity of solutions depends on the regularity of forcing terms, and we characterize the spaces where a bounded forcing term yields a bounded solution.   What we discover is a variety of different regimes, with completely different behaviors, depending on the exponent in the friction term.   We also provide counterexamples in order to show the optimality of our results. 
Marina Ghisi, Massimo Gobbino, Alain Haraux
math.AP