We prove weighted L 2 estimates for the Klein-Gordon equation perturbed with singular potentials such as the inverse-square potential. We then deduce the well-posedness of the Cauchy problem for this equation with small perturbations, and go on to discuss local smoothing and Strichartz estimates which improve previously known ones.2010 Mathematics Subject Classification. Primary: 35B45; Secondary: 35Q40.

We obtain some new Morawetz estimates for the Klein-Gordon flow of the formf H s where σ, s ≥ 0 and α > 0. The conventional approaches to Morawetz estimates with |x| −α are no longer available in the case of time-dependent weights |(x, t)| −α . Here we instead apply the Littlewood-Paley theory with Muckenhoupt A 2 weights to frequency localized estimates thereof that are obtained by making use of the bilinear interpolation between their bilinear form estimates which need to carefully analyze some relevant oscillatory integrals according to the different scaling of √ 1 − ∆ for low and high frequencies.

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There have been a lot of works concerning the Strichartz estimates for the perturbed Schrödinger equation by potential. These can be basically carried out adopting the well-known procedure for obtaining the Strichartz estimates from the weighted 𝐿 2 resolvent estimates for the Laplacian. In this paper we handle the Strichartz estimates without relying on the resolvent estimates. This enables us to consider various potential classes such as the Morrey-Campanato classes.