In this erratum we want to correct or modify some of the original statements and proofs in "Hadamard States, Adiabatic Vacua and the Construction of Physical States for Scalar Quantum Fields on Curved Spacetime" in Rev. Math. Phys. 8 (1996) 1091-1159.
E0. IntroductionIn the paper in question, we investigated Hadamard and adiabatic vacuum states for linear scalar field theories on curved spacetimes applying methods from microlocal analysis. In this erratum we want to correct or modify some of the original statements and proofs.One of the main results of the paper was the derivation of a sufficient condition on certain pseudodifferential operators which guarantees that quasifree states of the Klein-Gordon field constructed from such operators are Hadamard states (Theorem 3.12). We have to include here the additional assumption that the spacetime under consideration has a compact Cauchy surface. Moreover, due to an error in the proof of the theorem the statement is slightly modified [Eqs. (74) and (75)], without however affecting its essence. The reason for these modifications and a precise restatement of Theorem 3.12 are presented in Sec. E1.As an application of this theorem we had claimed in the paper that adiabatic vacuum states on Robertson-Walker spacetimes are Hadamard states (Theorem 3.24). This statement is wrong. In Sec. E2 we explain the origin of this error and prove the weaker statement that in the spatially compact case adiabatic vacua and Hadamard states generate unitarily equivalent GNS-representations. For a microlocal characterization of adiabatic vacuum states on arbitrary spacetimes and a clarification of their precise relation to Hadamard states in terms of wavefront sets we refer to [2].
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