arXiv subjects

Yasunori Fujii

Publications and source records attributed to Yasunori Fujii.

41 records · Page 3Linked to original sources

arXiv1996

Role of Regularization in Quantum Corrections to the Scalar-Tensor Theories of Gravity

We show that regularizing divergent integrals is crucially important when applied to the loop diagrams corresponding to quantum corrections to the coupling of the ``gravitational" scalar field due to the interaction among matter fields. We use the method of continuous spacetime dimensions to demonstrate that WEP is a robust property of the Brans-Dicke theory beyond the classical level, hence correcting our previous assertion of the contrary. The same technique can be used to yield the violation of WEP when applied to the scale-invariant theory, thus providing another reason for expecting fifth- force-type phenomena.

gr-qc↗

arXiv1996

Brans-Dicke Cosmology Corrected for a Quantum Effect due to the Scalar-Matter Coupling

Cosmological solutions of the Brans-Dicke theory are investigated by including a quantum effect coming from 1-loop correction of matter fields that couple to the scalar field. As the most serious result we face a cosmological ``constant'' in the original conformal frame which is shown to be ``physical'' after a careful analysis of the time variable employed in any of the conventional approaches. We find an ``attractor'' solution featuring no expansion during the radiation-dominated eras. To evade this unacceptable consequence, we suggest to modify one of the fundamental premises of the model, rendering the scalar field almost ``invisible.''

gr-qc↗

arXiv1996

A Mechanism for a small but nonzero cosmological constant

Based on a thoeretical model in which scalar fields play crucial roles, we propose a mechanism to better understand a cosmological constant expected to be small (nearly comparable with the critical density) but nonzero as suggested strongly by the recent observations. We emphasize that a step further is needed beyond the simplest scenario of a decaying cosmological constant, according to which the effective $Λ$ is not a true constant but decays like $t^{-2}$, thus explaining why any effect of $Λ$ which is assumed to be of the Planckian order of magnitude in the earliest Universe is at most 120 orders smaller today ($t\sim 10^{60}$ in units of the Planck time), without any extreme fine-tuning of the parameters. In addition to the overall smooth fall-off $\sim t^{-2}$, the total energy density, the sum of the contributions from the ordinary matter and the scalar fields, must show some leveling-off behavior, hence mimicking a truly constant $Λ$ to fit the observations. We find that the desired behavior can be obtained by introducing two scalar fields interacting with each other in a specific manner. Many aspects of this model are discussed in detail, including the real origin of the whole mechanism, and how the parameters and the initial conditions of the theory can be determined by the cosomological parameters at the present epoch as well as the past history of the Universe.

gr-qc↗

arXiv1995

How natural is a small but nonzero cosmological constant?

Based on our previous attempt, we propose a better way to understand a small but nonzero cosmological constant, as indicated by a number of recent observational studies. We re-examine the assumptions of our model of two scalar fields, trying to explain the basic mechanism resulting in a series of mini-inflations occuring nearly periodically with respect to $\ln t$ with $t$ the cosmic time. We also discuss how likely the solution of this type would be, depending on the choice of the parameters.

gr-qc↗

arXiv1994

Induced Violation of Weak Equivalence Principle in the Brans-Dicke Theory

A quantum correction to the Brans-Dicke theory due to interactions among matter fields is calculated, resulting in violation of WEP, hence giving a constraint on the parameter $ω$ far more stringent than accepted so far. The tentative estimate gives the lower bounds $\gsim 10^{6}$ and $\gsim 10^{8}$ for the assumed force-range $\gsim 1$m and $\gsim 1$AU, respectively.

gr-qc↗