QUANTUM TRANSITIONS IN EARLY UNIVERSE IN THE STRING THEORY WITH T-DUALITY

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(1) We have studied the time development of a universe with a torus structure in a string theory. In such a topologically non-trivial space, the T-duality plays as essential role for its time development. When the space is large enough most of closed strings stay there as small loop gas. The space there, which we call the x-space, is defined as the one canonically conjugate to the center of mass momentum of the small loops. As the size of the x-space becomes small, the string winding modes around the torus dominate and the dynamics there is better described by the new space coodinate x, which is conjugate to the winding number w.In the first article in the publication list, we have studied the time development of the torus space with a special care for the transition from x-space to x-space in 2+1 dimensional model, taking account of the back ground gravity and torsion fields.In the fourth article, we studied the possibility of signal exchange between the x-space and x-space through the shinkage of the universe which occurs at the transition period from x- to x-space. Although the statistical average of coordinate correlation DELTAx・DELTAx approaches to zero, time development in the x-space after the transition makes it difficult to observe the information from the x space at the present time.(2) In the superstring theory Kunitomo et.al.constructed a generating functional of scattering amplitudes for Type I-SST,and found the mechanism how the divergence cancellation in Type I-SST can be interpreted in the dual theory Type I'. In the latter, the disk amplitudes which have boundaries on the orbifoled precisely cancel those associated with tadpole amplitudes.(3) Kunitomo et al also constructed a topological field theory which describes the ground states of D-5 branes. As a result they showed that the Heisenberg algebras in the instanton moduli space can be interpreted as creation and annihilation operators of the D-5 branes.