Abstract. We compute explicitly the best constants and, by solving some functional equations, we find all maximizers for homogeneous Strichartz estimates for the Schrödinger equation and for the wave equation in the cases when the Lebesgue exponent is an even integer.

We look for the optimal range of Lebesque exponents for which inhomogeneous Strichartz estimates are valid. It is known that this range is larger than the one given by admissible exponents for homogeneous estimates. We prove inhomogeneous estimates in this larger range adopting the abstract setting and interpolation techniques already used by Keel and Tao for the endpoint case of the homogeneous estimates. Applications to Schrödinger equations are given, which extend previous work by Kato.

In this paper, we pursue a systematic treatment of the regularity theory for products and bilinear forms of solutions of the homogeneous wave equation. We discuss necessary and sufficient conditions for the validity of bilinear estimates, based on L2 norms in space and time, of derivatives of products of solutions. Also, we give necessary conditions and formulate some conjectures for similar estimates based on LqtLxr norms

We prove almost optimal local well-posedness for the coupled Dirac-Klein-Gordon (DKG) system of equations in 1 + 3 dimensions. The proof relies on the null structure of the system, combined with bilinear spacetime estimates of Klainerman-Machedon type. It has been known for some time that the Klein-Gordon part of the system has a null structure; here we uncover an additional null structure in the Dirac equation, which cannot be seen directly, but appears after a duality argument.

We show that constant functions are global maximizers for the adjoint Fourier restriction inequality for the sphere