2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36080We construct a distinguished set of positive and negative energy modes of the Klein-Gordon equation for any Born frame of reference in Minkowski's space-time. Unlike the case of a galilean frame of reference it is unclear whether this set of modes may be an appropriate basis to define the vacuum of a quantized scalar field in an accelerated cavity.To appear in "Analytical and Numerical Approaches to Relativity: Sources of Gravitational Radiation", ERE 1997, ed J.Stela, UIB, Palma de Mallorca, SpainGeneral Relativity and Quantum Cosmologytext