| Research Abstract |
Around 1989 when this project started, some questions were being raised of the geophysical experiments which had been accepted as an evidence for finite-range gravity, known also as a fifth force. It was eventually concluded in 1990 that no firm evidence was available. In the occasion of SLxth Marcel Grossmann Meeting on General Relativity held in 1991, for example, an agreement was reached that experiments give only upper bounds on the value of alpha which represents the relative strength of the fifth force. It seemed that no essentially new experiments were in sight. On the other hand, the detailed reevaluation of the theoretical models presented so far revealed that the predictions on the value of a as well as the forcerange are subject to uncertainties within- a few orders of magnitude. At the same time the naturalness of the theoretical motivations is even more obvious ; experiments of better accuracy are highly encouraged. In view of this situation, we carried out the project in
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the two directions.
1. Assuming that the fifth force is mediated by a scalar field, we investigated its roles from a wider point of view. We focused particularly on the connection with the cosmological constant problem in cosmology. Its importance is highly emphasized in the program of unifying particle physics and gravitation. It was pointed out that due to a scalar field -coupled nonmift-imally tolravity the cosmological constant can "decay" in time. A detailed analysis has shown that t ls is a very promising approach. We reached to a point in which we have a better understanding of the mechanism of reheating the universe, though it is yet to be seen how we explain the density perturbation equally successfully.
2. As an experiment to search for the finite-range gravity in still higher accuracy, we proposed to use a ultra-sensitive laser interferometer which is now being developed in the program of gravity-wave detection. We believe that a further progress can be achieved by utilizing the technique of lasers with extremely narrow line width. Less
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