Representation Theorems for Indefinite Quadratic Forms Revisited

Abstract

The first and second representation theorems for sign-indefinite, not necessarily semi-bounded quadratic forms are revisited. New straightforward proofs of these theorems are given. A number of necessary and sufficient conditions ensuring the second representation theorem to hold is proved. A new simple and explicit example of a self-adjoint operator for which the second representation theorem does not hold is also provided.

This work is supported in part by the Deutsche Forschungsgemeinschaft

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