2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/187495We construct a new class of physical states of the free Klein-Gordon field in Robertson-Walker spacetimes. This is done by minimizing the expectation value of smeared stress-energy. We get an explicit expression for the state depending on the smearing function. We call it a state of low energy. States of low energy are an improvement of the concept of adiabatic vacua on Robertson-Walker spacetimes. The latter are approximations of the former. It is shown that states of low energy are Hadamard states.24 pages, minor changes, acknoledgements addedGeneral Relativity and Quantum Cosmologytext