arXiv subjects

Yasunori Fujii

Publications and source records attributed to Yasunori Fujii.

At least 37 records · Page 2Linked to original sources

arXiv2005

How strongly does dating meteorites constrain the time-dependence of the fine-structure constant?

We review our argument on the nature of the so-called meteorite constraint on the possible time-dependence of the fine-structure constant, emphasizing that dating meteorites at the present time is different in principle from searching directly for the traces in the past, as in the Oklo phenomenon and the QSO absorption lines. In the related literature, we still find some arguments not necessarily consistent with this difference to be taken properly into account. It does not immediately follow that any model-dependent approaches are useless in practice, though we cannot help suspecting that dating meteorites is no match for the Oklo and the QSO in probing the time-variability of the fine-structure constant, at this moment. Some of the relevance to the QSO data particularly in terms of the scalar field will be discussed.

hep-ph↗

arXiv2005

A possible new interpretation of the results of $Δα/α$ from QSO absorption lines

The measurement of $Δα/α$ from the QSO absorption lines of Fe_II taken at two different redshifts (Quast et al, Levshakov et al) is compared with the result based on the 23 data points also obtained from VLT/UVES (Chand et al), to demonstrate that the apparent oscillatory time-dependence fitting the latter taken at face value is reinforced by the former claimed to be of much better accuracy.

astro-ph↗

arXiv2004

$Δα/α$ from QSO absorption lines driven by an oscillating scalar field

The new result on the QSO absorption lines from VLT-UVES sample is compared with the past reports on the time-variability of the fine-structure "constant" derived from the Keck/HIRES observation, on the basis of an oscillatory behavior of the scalar field supposed to be responsible for the cosmological acceleration.

astro-ph↗

arXiv2004

Some aspects of the scalar-tensor theory

The scalar-tensor theory of gravitation has been and still is one of the most widely discussed "alternative theories" to General Relativity (GR). Despite nearly half a century of its age, it continues to attract renewed interests of not only theorists but also experimentalists when we now face such issues like the accelerating universe and possible time-variability of the fine-structure constant, both viewed as something beyond the standard GR. It appears that the theory provides realistic results sometimes even beyond what is expected from the quintessence approach aimed primarily to be more phenomenological. It seems nevertheless as if some of the unique aspects of this theory are not fully understood, even leading to occasional confusions. I try in my lectures, partly using the contents of our book (Y.F. and K. Maeda, Scalar-tensor theory of gravitation, Cambridge University Press, 2003), to discuss some of the most crucial concepts starting from elementary introduction to the theory. Particular emphases will be placed on the unique features of the nonminimal coupling term, the roles of the conformal transformations together with the choice of a physical conformal frame and the value of the coupling strength to the matter. Readers are advised to refer to the references for more details.

gr-qc↗

arXiv2003

Astrophysical constraints on hypothetical variability of fundamental constants

(Abridged) Many-multiplet (MM) method applied to three inhomogeneous samples of Keck/HIRES quasar absorption spectra gives a shift in the value of the fine-structure constant of Delta alpha/alpha = (-5.4+/-1.2) 10^{-6} in the redshift range 0.2 < z < 3.7 (Murphy et al. 2003).The 1sigma error is, however, much too small and cannot be maintained by current observations of quasars. We present a modified MM method to set an upper limit on Delta alpha/alpha from a homogeneous sample of FeII lines identified in the up-to-date best quality VLT/UVES spectrum of HE 0515-4414. Our result is Delta alpha/alpha = (1.1+/-1.1) 10^{-5} at z = 1.149. Theoretical models of the fundamental physical interactions predict that the proton-to-electron mass ratio (mu = m_p/m_e) may relate to the shift in Delta alpha/alpha as Delta mu/mu = R Delta alpha/alpha. We use VLT/UVES high-resolution observations of molecular hydrogen H2 ultraviolet absorption lines at z = 3.025 toward Q 0347-3818 to bound the value of R. The obtained constraints on Delta ln mu = (2.1+/-3.6) 10^{-5} and on Delta ln alpha = (1.1+/-1.1) 10^{-5} rule out vary large values of |R| > 6.

astro-ph↗

arXiv2003

Re/Os constraint on the time-variability of the fine-structure constant

We argue that the accuracy by which the isochron parameters of the decay $^{187}{\rm Re}\to ^{187}{\rm Os}$ are determined by dating iron meteorites may not directly constrain the possible time-dependence of the decay rate and hence of the fine-structure constant $α$. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the QSO absorption lines are re-examined.

hep-ph↗

arXiv2003

Time-variability of the fine-structure constant expected from the Oklo constraint and the QSO absorption lines

The data from the QSO absorption lines indicating a nonzero time-variability of the fine-structure constant has been re-analyzed on the basis of a "damped-oscillator" fit, as motivated by the same type of behavior of a scalar field, dilaton, which mimics a cosmological constant to understand the accelerating universe. We find nearly as good fit to the latest data as the simple weighted mean. In this way, we offer a way to fit the more stringent result from the Oklo phenomenon, as well.

astro-ph↗

arXiv2003

Mass of the dilaton and the cosmological constant

One might raise a question if the gravitational scalar field (dilaton) mediates a finite-range force between local objects still behaving globally as being massless to implement the scenario of a decaying cosmological constant. We offer a non-negative reply by a detailed analysis of the field-theoretical quantization procedure in relation to the observationally required suppression of the vacuum-energy.

gr-qc↗

arXiv2002

Varying Fine-Structure Constant and the Cosmological Constant Problem

We start with a brief account of the latest analysis of the Oklo phenomenon providing the still most stringent constraint on time-variability of the fine- structure constant $α$. Comparing this with the recent result from the measurement of distant QSO's appears to indicate a non-uniform time-dependence, which we argue to be related to another recent finding of the accelerating universe. This view is implemented in terms of the scalar-tensor theory, applied specifically to the small but nonzero cosmological constant. Our detailed calculation shows that these two phenomena can be understood in terms of a common origin, a particular behavior of the scalar field, dilaton. We also sketch how this theoretical approach makes it appropriate to revisit non- Newtonian gravity featuring small violation of Weak Equivalence Principle at medium distances.

gr-qc↗

arXiv2002

Nuclear Data in Oklo and Time-Variability of Fundamental Coupling Constants

We re-examined Shlyakhter's analysis of the Sm data in Oklo. With a special care of minimizing contamination due to the inflow of the isotope after the end of the reactor activity, we confirmed that his result on the time-variability of the fine-structure constant, $|\dotα/α|\lsim 10^{-17}{\rm y}^{-1}$, was basically correct. In addition to this upper bound, however, we obtained another result that indicates a different value of $α$ 2 billion years ago. We add comments on the recent result from QSO's.

hep-ph↗

arXiv2002

Possible link between the changing fine-structure constant and the accelerating universe via scalar-tensor theory

In 1976, Shlyakhter showed that the Sm data from Oklo results in the upper bound on the time-variability of the fine-structure constant: $|\dotα/α| \lsim 10^{-17}{\rm y}^{-1}$, which has ever been the most stringent bound. Since the details have never been published, however, we recently re-analyzed the latest data according to Shlyakhter's recipe. We nearly re-confirmed his result. To be more precise, however, the Sm data gives either an upper-bound or an "evidence" for a changing $α$: $\dotα/α= -(0.44 \pm 0.04)\times 10^{-16}{\rm y}^{-1}$. A remark is made to a similar re-analysis due to Damour and Dyson. We also compare our result with a recent "evidence" due to Webb et al, obtained from distant QSO's. We point out a possible connection between this time-dependence and the behavior of a scalar field supposed to be responsible for the acceleration of the universe, also revealed recently.

astro-ph↗

arXiv2000

Cosmological Constant, Quintessence and Scalar-Tensor Theories of Gravity

We show how the scalar field, a candidate of quintessence, in a proposed model of the scalar-tensor theories of gravity provides a way to understand a small but nonzero cosmological constant as indicated by recent observations. A particular emphasis is placed on the effort to inherit the success of the scenario of a decaying cosmological constant. Discussions of a possible link to non-Newtonian gravity, the coincidence problem, the issue of time-variability of coupling constants as well as the chaos-like nature of the solution are also included in a new perspective.

gr-qc↗

arXiv2000

The nuclear interaction at Oklo 2 billion years ago

We re-examine the effort to constrain the time-variability of the coupling constants of the fundamental interactions by studying the anomalous isotopic abundance of Sm observed at the remnants of the natural reactors which were in operation at Oklo about 2 billion years ago, in terms of a possible deviation of the resonance energy from the value observed today. We rely on new samples that were carefully collected to minimize natural contamination and also on a careful temperature estimate of the reactors. We obtain the upper bound $(-0.2\pm 0.8)\times 10^{-17}$ ${\rm y}^{-1}$ on the fractional rate of change of the electromagnetic as well as the strong interaction coupling constants. Our result basically agrees with and even suggests some improvement of the result due recently to Damour and Dyson. Strictly speaking, however, we find another range of the resonance energy shift indicating a nonzero time variation of the constants. We find a rather strong but still tentative indication that this range can be ruled out by including the Gd data, for which it is essential to take the effect of contamination into account.

hep-ph↗

arXiv1999

Quintessence, scalar-tensor theories and non-Newtonian gravity

We discuss some of the issues which we encounter when we try to invoke the scalar-tensor theories of gravitation as a theoretical basis of quintessence. One of the advantages of appealing to these theories is that they allow us to implement the scenario of a ``decaying cosmological constant,'' which offers a reasonable understanding of why the observed upper bound of the cosmological constant is smaller than the theoretically natural value by as much as 120 orders of magnitude. In this context, the scalar field can be a candidate of quintessence in a broader sense. We find, however, a serious drawback in the prototype Brans-Dicke model with $Λ$ added; a static universe in the physical conformal frame which is chosen to have constant particle masses. We propose a remedy by modifying the matter coupling of the scalar field taking advantage of scale invariance and its breakdown through quantum anomaly. By combining this with a conjecture on another cosmological constant problem coming from the vacuum energy of matter fields, we expect a possible link between quintessence and non-Newtonian gravity featuring violation of Weak Equivalence Principle and intermediate force range, likely within the experimental constraints. A new prediction is also offered on the time-variability of the gravitational constant.

gr-qc↗

arXiv1999

A two-scalar model for a small but nonzero cosmological constant

We revisit a model of the two-scalar system proposed previously for understanding a small but nonzero cosmological constant. The model provides solutions of the scalar-fields energy $ρ_s$ which behaves truly constant for a limited time interval rather than in the way of tracker- or scaling-type variations. This causes a mini-inflation, as indicated by recent observations. As another novel feature, $ρ_s$ and the ordinary matter density $ρ_m$ fall off always side by side, but interlacing, also like (time)$^{-2}$ as an overall behavior in conformity with the scenario of a decaying cosmological constant. A mini-inflation occurs whenever $ρ_s$ overtakes $ρ_m$, which may happen more than once, shedding a new light on the coincidence problem. We present a new example of the solution, and offer an intuitive interpretation of the mechanism of the nonlinear dynamics. We also discuss a chaos-like nature of the solution.

gr-qc↗

arXiv1998

What can we do on gravity with antihydrogens?

We discuss the implications of the proposed gravitational redshift experiment on antihydrogens. We show that the result should be the same as on hydrogens in spite of different free-fall accelerations (WEP violation) which may occur if there is a vector fifth-force field. We emphasize the experiment is unique in the sense that it tests the Equivalence Principle expressed in its ultimate form, proposed to be called UEP, directly without being disturbed by the effect of possible presence of a scalar fifth-force field.

gr-qc↗

arXiv1998

Nonzero $Ω_Λ$ and a new type of the dissipative structure

We revisit the proposed theoretical model for a small but nonzero cosmological constant which seems supported increasingly better by recent observations. The model features two scalar fields which interact with each other through a specifically chosen nonlinear potential. We find a very sensitive dependence of the solutions of the scalar field equations on the initial values. We discuss how the behavior is similar to and different from those in well-known chaotic systems, coming to suggest an interesting new type of the dissipative structure.

gr-qc↗

arXiv1997

Choosing a conformal frame in scalar-tensor theories of gravity with a cosmological constant

Cosmological solutions of the Brans-Dicke theory with an added cosmological constant are investigated with an emphasis to select a conformal frame in order to implement the scenario of a decaying cosmological constant, featuring an ever growing scalar field. We focus particularly on Jordan frame, the original frame with the nonminimal coupling, and conformally transformed Einstein frame without it. For the asymptotoic 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 scalar-matter coupling, thus making Einstein frame acceptable. The invariacne is broken as a quantum anomaly effect due to the non-gravitational interactions, entailing naturally the fifth force, characterized by a finite force-range and WEP violation. A tentative estimate shows that the theoretical prediction is roughly consistent with the observational upper bounds. Further efforts to improve the experimental accuracy is strongly encouraged.

gr-qc↗