Choosing a Conformal Frame in Scalar-Tensor Theories of Gravity with a Cosmological Constant

概要

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Cosmological solutions of the Brans-Dicke theory with an added cosmological constant are investigated with an emphasis on selecting a conformal frame in order to implement the scenario of a decaying cosmological constant, featuring an ever-growing scalar field. We focus particularly on the Jordan frame, the original frame with nonminimal coupling, and the conformally transformed Einstein frame without it. For the asymptotic attractor solutions as well as the "hesitation behavior", we find that none of these conformal frames can be accepted as the basis of analyzing primordial nucleosynthesis. As a remedy, we propose to modify the prototype BD theory by introducing a scale-invariant scale-matter coupling, thus making the Einstein frame acceptable. The invariance is broken as a quantum anomaly effect due to non-gravitational interactions, naturally entailing a fifth force, characterized by a finite force-range and violation of weak equivalence principle (WEP). A tentative estimate shows that the theoretical predication is roughly consistent with the observational upper bounds. Further efforts to improve experimental accuracy are strongly encouraged.
理論物理学刊行会の論文
1998-04-25