We show the small data solvability of suitable semilinear wave and Klein–Gordon
equations on geometric classes of spaces, which include so-called asymptotically
de Sitter and Kerr–de Sitter spaces as well as asymptotically Minkowski
spaces. These spaces allow general infinities, called conformal infinity in
the asymptotically de Sitter setting; the Minkowski-type setting is that of
nontrapping Lorentzian scattering metrics introduced by Baskin, Vasy and
Wunsch. Our results are obtained by showing the
global Fredholm property,
and indeed invertibility, of the underlying linear operator on suitable
-based
function spaces, which also possess appropriate algebra or more complicated
multiplicative properties. The linear framework is based on the b-analysis, in the
sense of Melrose, introduced in this context by Vasy to describe the asymptotic
behavior of solutions of linear equations. An interesting feature of the analysis is that
resonances, namely poles of the inverse of the Mellin-transformed b-normal
operator, which are “quantum” (not purely symbolic) objects, play an important
role.