Vistas in Curved Space-Time Quantum Field Theory.

The problem of how to define vacuum or particle states in curved space quantum field theory is reviewed and a criterion for selecting the physical "vacuum" state is advanced. The properties of quantum field theory for accelerated observers are examined. We find that the particle detector and canonical quantization approaches are not contradictory, and claims otherwise originate in an incorrect choice of rest frame coordinates. Event horizons in the coordinate system are a sufficient but not a necessary condition for the effect of inequivalent vacua and particle detection. We also find that: an accelerated "particle detector" will emit thermal radiation to nearby inertial observers, the response of such a detector can be anisotropic, and that interpretations of effect as bremstrahlung are wrong. An electron in a constant external E-field is found to be in a thermal state, emitting thermal radiation due to a non-perturbative effect in QED. The temperature is compatible with that found for accelerated observers. No evolution of pure states to mixed states is indicated. We exhibit a particle production for scalar (lamda)(phi)('4) theory in de Sitter space, related to the accelerated observer and QED results. The production rate is proportional to the number of particles present, and thus grows exponentially. General arguments strongly suggest that this process is generic to any renormalizable interacting theory on de Sitter space. Non -local effects in a class of particle production mechanisms in curved space-time are shown to dynamically cause a decrease in the effective cosmological constant. This has implications for inflationary models of the early universe and for the cosmological constant problem. Constant curvature solutions are found for the semiclassical Einstein equations coupled to N massless conformaly invariant quantum fields, with bare cosmological constant (LAMDA)(,(phi)). Their existence and stability under infinitesimal perturbations depends upon (LAMDA)(,(phi)) and the spins of the fields present. Anti-de Sitter space is unstable for most spins. It is shown that, contrary to recent claims, there is no floating point for boxes lowered near a black hole. Despite this, the generalized second law of thermodynamics remains valid without a bound on S/E so there is no need to impose a bound as a new fundamental law of physics.