Browsing by Author "Seriu, Masafumi"

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    On the relation between causality and topology in the semiclassical universe
    (2015-01-13) Seriu, Masafumi; Singh, T. P.
    We systematically derive a series of validity conditions for semiclassical gravity and deduce a strong restriction on the possible topology of the semiclassical universe founded on the path-integral formalism. We begin with the investigation of the fundamental setting of quantum gravity. We show that, in order to obtain the causal semiclassical Einstein equation at the later stage of the universe, we have to regard the in-in path-integral formalism as fundamental in quantum gravity. We then perform the stationary phase approximation for the gravity mode. From the first variation of the phase , we obtain a series of validity conditions of semiclassical gravity in a completely general manner.
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    Topology selection through quantum cosmology
    (2015-01-13) Seriu, Masafumi
    We argue that in order to obtain causal semiclassical Einstein equation at the stage much later than the planck time, we have to regard the in-in pathintegral formalism as fundamental in quantum cosmology. We then deduce that any classical universe should allow at least one maximal surface. If the natural energy condition holds, this mean that (1) the classical universe should be a wheeler universe, i.e. it start from and end in a singularity, and (2) the possible topologies of classical universe are strongly restricted. The implication of the recent observation of the cosmic microwave background radiation is also discussed.