Abstract. Let X be a space of homogeneous type and let L be a nonnegative self-adjoint operator on L 2 (X) enjoying Gaussian estimates. The main aim of this paper is twofold. Firstly, we prove (local) nontangential and radial maximal function characterizations for the local Hardy spaces associated to L. This gives the maximal function characterization for local Hardy spaces in the sense of Coifman and Weiss provided that L satisfies certain extra conditions. Secondly we introduce local Hardy spaces associated with a critical function ρ which are motivated by the theory of Hardy spaces related to Schrödinger operators and of which include the local Hardy spaces of Coifman and Weiss as a special case. We then prove that these local Hardy spaces can be characterized by (local) nontangential and radial maximal functions related to L and ρ, and by global maximal functions associated to 'perturbations' of L. We apply our theory to obtain a number of new results on maximal characterizations for the local Hardy type spaces in various settings ranging from Schrödinger operators on manifolds to Schrödinger operators on connected and simply connected nilpotent Lie groups.

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Let $\La$ be a Schr\"odinger operator with\ud inverse square potential $a|x|^{-2}$ on $\Rd, d\geq 3$. The main aim of this paper is to prove weighted estimates for fractional powers of $\La$. The proof is based on weighted Hardy inequalities and weighted inequalities for square functions associated to $\La$. As an application, we obtain smoothing estimates regarding the propagator $e^{it\La}$