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We discuss the quantization of linearized gravity on globally hyperbolic,asymptotically flat, vacuum spacetimes and the construction of distinguishedstates which are both of Hadamard form and invariant under the action of allbulk isometries. The procedure, we follow, consists of looking for arealization of the observables of the theory as a sub-algebra of an auxiliary,non-dynamical algebra constructed on future null infinity $\Im^+$. Theapplicability of this scheme is tantamount to proving that a solution of theequations of motion for linearized gravity can be extended smoothly to $\Im^+$.This has been claimed to be possible provided that a suitable gauge fixingcondition, first written by Geroch and Xanthopoulos, is imposed. We review itsdefinition critically showing that there exists a previously unnoticedobstruction in its implementation leading us to introducing the concept ofradiative observables. These constitute an algebra for which a Hadamard stateinduced from null infinity and invariant under the action of all spacetimeisometries exists and it is explicitly constructed.

Radiative observables for linearized gravity on asymptotically flat spacetimes and their boundary induced states