Project Euclid

Let $A$ be the generator of an analytic semigroup on a Banach space $X$. We study the Sobolev regularity of the solutions $u$ of the problem $u'(t)=Au(t)+f(t)$, for almost every $t\in (0,T)$, $u(0)=u_0$. Using extrapolation theory we can investigate optimal conditions for the data $f$ and $u_0$ guaranteeing $u\in W^{\alpha,p}(0,T;X)$ and obtain new existence results for generalized as well as differentiable solutions for parabolic equations.