Search

We have conducted Q-band (30 GHz $-$ 50 GHz) line survey observations toward a carbon-chain emission peak in the Serpens South cluster-forming region with the extended Q-band (eQ) receiver installed on the Nobeyama 45 m radio telescope. Approximately 180 lines have been detected including tentative detection, and these lines are attributed to 52 molecules including isotopologues. It has been found that this position is rich in carbon-chain species as much as Cyanopolyyne Peak in Taurus Molecular Cloud-1 (TMC-1 CP), suggesting chemical youth. Not only carbon-chain species, but several complex organic molecules (CH$_3$OH, CH$_3$CHO, HCCCHO, CH$_3$CN, and tentatively C$_2$H$_3$CN) have also been detected, which is similar to the chemical complexity found in evolved prestellar cores. The HDCS/H$_2$CS ratio has been derived to be $11.3 \pm 0.5$ %, and this value is similar to the prestellar core L1544. The chemically young features that are similar to the less-dense starless core TMC-1 CP ($10^4$ cm$^{-3}$ $-$ $10^5$ cm$^{-3}$) and chemically evolved characters which resemble the dense prestellar core L1544 ($\sim 10^6$ cm$^{-3}$) mean that the clump including the observed position is a pre-cluster clump without any current star formation activity., Comment: Accepted for publication in Publications of the Astronomical Society of Japan (PASJ), 32 pages, 9 figures, 6 tables

We report on the development and commissioning of a new Q-band receiver for the Nobeyama 45-m telescope, covering 30--50 GHz with a receiver noise temperature of about 15 K. We name it eQ (extended Q-band) receiver. The system noise temperatures for observations are measured to be $\sim$ 30 K at 33 GHz and $\sim$ 75 K at 45 GHz. The Half-Power-Beam-Width (HPBW) is around 38\arcsec at 43 GHz. To enhance the observation capability, we tested the smoothed bandpass calibration technique and demonstrated the observation time can be significantly reduced compared to the standard position switch technique. The wide-bandwidth capability of this receiver provides precise determination of rest frequencies for molecular transitions with an accuracy of a few kHz through simultaneous observations of multiple transitions. Particularly, we determined the rest frequency of SO ($J_N$ = $1_0$--$0_1$) to be 30.001542 GHz, along with the rest frequency of CCS ($J_N$ = $4_3$--$3_2$) being 45.379033 GHz, adopting CCS ($J_N$ = $3_2$--$2_1$) at 33.751370 GHz as a reference line. The SO profile shows a double peak shape at the Cyanopolyyne Peak (CP) position of the Taurus Molecular Cloud-1 (TMC-1). The SO peaks coincide well with the CCS sub-components located near the outer parts of the TMC-1 filament. We interpret that the gravitational infall of TMC-1 generates shocks which enhance the SO abundance. The TMC-1 map shows that carbon-chain molecules are more abundant in the southern part of the filament, whereas SO is more abundant in the northern part. The eQ's excellent sensitivity allowed us to detect faint CO ($J$ = 1--0) spectra from the high-redshift object at a redshift of 2.442. Our receiver is expected to open new avenues for high-sensitivity molecular line observations in the Q-band., Comment: 20 pages, 18 figures, PASJ in press

Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220-440 GHz band in a single shot, corresponding to a redshift range of $z$=3.3-7.6 for the ionized carbon emission ([C II] 158 $\mu$m). The first-light experiment of DESHIMA 1.0, using the 332-377 GHz band, has shown an excellent agreement among the on-sky measurements, the lab measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign., Comment: 9 pages, 4 figures, 1 table, accepted for publication in the Journal of Low Temperature Physics for the LTD19 special issue

We report the current status of the NASCO (NAnten2 Super CO survey as legacy) project which aims to provide all-sky CO data cube of southern hemisphere using the NANTEN2 4-m submillimeter telescope installed at the Atacama Desert through developing a new multi-beam receiver and a new telescope control system. The receiver consists of 5 beams. The four beams, located at the four corners of a square with the beam separation of 720$''$, are installed with a 100 GHz band SIS receiver having 2-polarization sideband-separation filter. The other beam, located at the optical axis, is installed with a 200 GHz band SIS receiver having 2-polarization sideband-separation filter. The cooled component is modularized for each beam, and cooled mirrors are used. The IF bandwidths are 8 and 4 GHz for 100 and 200 GHz bands, respectively. Using XFFTS spectrometers with a bandwidth of 2 GHz, the lines of $^{12}$CO, $^{13}$CO, and C$^{18}$O of $J$=1$-$0 or $J$=2$-$1 can be observed simultaneously for each beam. The control system is reconstructed on the ROS architecture, which is an open source framework for robot control, to enable a flexible observation mode and to handle a large amount of data. The framework is commonly used and maintained in a robotic field, and thereby reliability, flexibility, expandability, and efficiency in development are improved as compared with the system previously used. The receiver and control system are installed on the NANTEN2 telescope in December 2019, and its commissioning and science verification are on-going. We are planning to start science operation in early 2021., Comment: submitted to SPIE Astronomical Telescopes + Instrumentation (AS20), paper No. 11453-146

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter-bank and Microwave Kinetic Inductance Detector (MKID) to investigate dusty star-burst galaxies in the distant universe at millimeter and submillimeter wavelength. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV, 0.4-3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of $1\sigma=4$%, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs, and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array., Comment: Accepted for publication in the Journal of Low Temperature Physics for LTD-18 special issue

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/\Delta F \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible., Comment: Published in Nature Astronomy. SharedIt Link to the full published paper: https://rdcu.be/bM2FN

A new estimate of the mass of the pseudo dilaton is offered by following the funda- mental nature that a massless Nambu-Goldstone boson, called a dilaton, in the Einstein frame acquires a nonzero mass through the loop effects which occur with the Higgs field in the relativistic quantum field theory as described by poles of D, spacetime dimensionality off the physical value D = 4. Naturally the technique of dimensional regulairzation is fully used to show this pole structure to be suppressed to be finite by what is called a Classical-Quantum-Interplay, to improve our previous attempt. Basically the same anal- ysis is extended to derive also the coupling of a pseudo dilaton to two photons., Comment: 14 pages, 1 figure; A contribution to the forthcoming book, "At The Frontier of Spacetime -- Scalar-Tensor Theory, Bells inequality, Mach's Principle, Exotic Smoothness." dedicated to Carl Brans on his 80th Birthday. Springer, 2016."

We discuss how we remove a huge discrepancy between the theory of a cosmological constant, due to the zero-point energies of matter fields, and the observation. The technique of dimensional regularization plays a decisive role. We eventually reach the desired behavior of the vacuum densities falling off like t^{-2}, allowing us to understand how an extremely small result comes about naturally. As a price, however, the zero-point energy vacuum fails to act as a true cosmological constant. Its expected role responsible for the observed accelerating universe is then to be inherited by the gravitational scalar field, dark energy, as we suggest in the scalar-tensor theory., Comment: 9 pages

The observed accelerating universe indicates the presence of Dark Energy which is probably interpreted in terms of an extremely light gravitational scalar field. We suggest a way to probe this scalar field which contributes to optical light-by-light scattering through the resonance in the quasi-parallel collision geometry. As we find, the frequency-shifted photons with the specifically chosen polarization state can be a distinct signature of the scalar-field-exchange process in spite of the extremely narrow width due to the gravitationally weak coupling to photons. Main emphasis will be placed in formulating a prototype theoretical approach, then showing how the weak signals from the gravitational coupling are enhanced by other non-gravitational effects at work in laser experiments., Comment: 20 pages, 6 figure. Accepted by Progress of Theoretical Physics

The discovery of the accelerating universe indicates strongly the presence of a scalar field which is not only expected to solve today's version of the cosmological constant problem, or the fine-tuning and the coincidence problems, but also provides a way to understand dark energy. It has also been shown that Jordan's scalar-tensor theory is now going to be re-discovered in the new lights. In this letter we suggest a way to search for the extremely light scalar field by means of a laboratory experiment on the low-energy photon-photon interactions with the quasi-parallel incident beams., Comment: 10 pages, 2 figures

Theoretical background of our proposed relation between the accelerating universe and the time-variability of the fine-structure constant is discussed, based on the scalar-tensor theory, with emphases on the intuitive aspects of underlying physical principles. An important comment is added on the successful understanding of the size of the effective cosmological constant responsible for the acceleration, without appealing to fine-tuning parameters., Comment: 6 pages. In Press in IAU 2009 JD9 conference proceedings. MmSAIt, vol.80, eds. Paolo Molaro and Elisabeth Vangioni

The accelerating universe is closely related to today's version of the cosmological constant problem; fine-tuning and coincidence problems. We show how successfully the scalar-tensor theory, a rather rigid theoretical idea, provides us with a simple and natural way to understand why today's observed cosmological constant is small only because we are old cosmologically, without fine-tuning theoretical parameters extremely., Comment: 6 pages, 1 figure, based on a conference talk

In the scalar-tensor theory of gravitation it seems nontrivial to establish if solutions of the cosmological equations in the presence of a cosmological constant behave as attractors independently of the initial values. We develop a general formulation in terms of two-dimensional phase space. We show that there are two kinds of fixed points, one of which is an attractor depending on the coupling constant and equation of state. In the case with a power-law potential in the Jordan frame, we also find new type of inflation caused by the coupling to the matter fluid.

An attempt is made for a new type of analysis of the time-variability of the fine-structure constant trying to fit the most recent result from the laboratory measurements, the Oklo constraint and the data from the QSO absorption lines all in consistency with the accelerating universe., Comment: 8 pages, 3 figures. Revised references

Apart from the suspected violation of the CPT invariance, we might expect if the measurements of antihydrogen atoms provide testing Weak Equivalence Principle (WEP) in the gravitational phenomena. We start with how its violation can be related to the expected idea of unification of particle physics and gravitation, an attempt beyond the standard theories, including general relativity of Einstein. A particular emphasis will be placed on the issue of an accelerating universe, a rather recent development since nearly 10 years ago, suggesting a strong motivation toward attempts beyond the conventional concepts of the traditional cosmology. We face today's version of the cosmological constant problem. A candidate of the new ingredient appears to be provided by a scalar field, sometimes under the names like quintessence or dark-energy. In this article, we discuss the subject from a point of view of a more theoretical approach based on the scalar-tensor theory of gravitation. By exploiting the concepts of conformal transformations and conformal frames unique to this type of approach, we show that a successful understanding of the observed cosmological acceleration entails an unexpected outcome of breakdown of WEP, which may show up as a distinct behavior between hydrogen and antihydrogen in the gravitational influence, from a further wider perspective including a vector field as well. We intended to introduce most of the new concepts as plainly and briefly as possible, according to the nature of the talk. On the other hand, however, we find it also useful to go into some more details, depending on the interests of individuals among the audience. For a compromise, we decided to add a number of footnotes which were not delivered during the presentation, but might be helpful in the proceedings published later., Comment: 12 pages, 5 figures. Prepared for the Proceedings of the Workshop on Cold Antimatter Plasmas and Application to Fundamental Physics, February 20-22, 2008, Naha, Okinawa, Japan. Due to a technical problem, diagrams in Fig. 4 in the original Proceedings are replaced here by simplified versions. Corrected fig

The scalar-tensor theory is plagued by nagging questions if different conformal frames, in particular the Jordan and Einstein conformal frames, are equivalent to each other. As a closely related question, there are opposing views on which of the two conformal frames is physically acceptable. Reinforcing our previous claims, we offer replies based on a cosmological model of the scalar-tensor theory, believed to be a promising theory for understanding the accelerating universe, as well as today's version of the cosmological constant problem. Exploiting the advantage that this model admits analytical asymptotic solutions, our argument does not depend on whether the underlying theory is invariant under conformal transformations. Our argument provides partial support for the claimed "equivalence," but we also present examples that require more careful analyses exploiting field equations. We also point out that the Jordan conformal frame is suitable for an interpretation in terms of unification theories in physics, for example, string theory and the Kaluza-Klein approach, while the Einstein conformal frame may be acceptable as a physical conformal frame under two conditions: (i) the simplest constant $\Lambda$ term in the Lagrangian in the Jordan conformal frame; (ii) the revised form of the conventional Brans-Dicke model based on the validity of weak equivalence principle., Comment: 36 pages with 1 figure

We present a theoretical calculation on the time-variability of the fine-structure constant to fit the result of the recent precise analysis of the measurement of the QSO absorption lines. We find the parameters and initial values of the scalar-tensor theory to be determined much more accurately than fitting the accelerating universe itself, but leading not to easy detections of the effect on the equation of state of the dark energy in the earlier epochs., Comment: 9 pages, 9 figures. Revised interpretation of the theoretical fit; more recent references

The effect of the massless gravitational scalar field assumed to couple directly to the Maxwell field to the solar-system experiments is estimated. We start with discussing the theoretical significances of this coupling. Rather disappointingly, however, we find that the scalar-field parameters never affect the observation in the limit of the geometric optics, indicating a marked difference from the well-known contribution through the spacetime metric., Comment: LaTex 10 pages

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., Comment: 18 pages, 6 figures, review article

The measurement of $\Delta\alpha/\alpha$ 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., Comment: 5 pages, 2 figures

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., Comment: 12 pages 4 figures. Based on the talks delivered at Second Advanced Research Workshop, Gravity, Astrophysics, and Strings, Kiten, Bulgaria, June 10-16, 2004

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., Comment: 7 pages, 7 figures. v2: Divided into sections, added Fig. 7 and references, including minor changes. v3: 9 pages. Revised for journal publication with additional references

The Oklo phenomenon, natural fission reactors which had taken place in Gabon about 2 billion years ago, provides one of the most stringent constraints on the possible time-variability of the fine-structure constant $\alpha$. We first review briefly what it is and how reliable it is in constraining $\alpha$. We then compare the result with a more recent result on the nonzero change of $\alpha$ obtained from the observation of the QSO absorption lines. We suggest a possible way to make these results consistent with each other in terms of the behavior of a scalar field which is expected to be responsible for the acceleration of the universe., Comment: 19 pages, 2 jpg and 10 eps figures, delivered at Astrophysics, Clocks and Fundamental Constants, 16-18 June 2003, Bad Honnef, Germany, to be published in Lecture Notes in Physics, Springer. v2 revises jpg files, adds 2 footnotes and 2 references

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 $\alpha$. 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., Comment: 7 pages, 3 figures; v2, revised top sentence on p. 6

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., Comment: 10 pages, 4 figures. Expanded section 2 and added discussion on the Re decay in section 4

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., Comment: 9 pages LaTeX 1 figure; an added reference and partial revisions

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 $\alpha$. 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., Comment: Delivered at JENAM 2002, Porto, Portugal, 2-7 September, 2002; 5 pages LaTex, 3 figures; typographical errors corrected

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, $|\dot{\alpha}/\alpha |\lsim 10^{-17}{\rm y}^{-1}$, was basically correct. In addition to this upper bound, however, we obtained another result that indicates a different value of $\alpha$ 2 billion years ago. We add comments on the recent result from QSO's., Comment: 3 pages, 1 figure, presented at Int. Conf. on Nuclear Data for Science and Technology, ND2001, 7-12 October, 2001, Tsukuba, Japan

In 1976, Shlyakhter showed that the Sm data from Oklo results in the upper bound on the time-variability of the fine-structure constant: $|\dot{\alpha}/\alpha| \lsim 10^{-17}{\rm y}^{-1}$, 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 $\alpha$: $\dot{\alpha}/\alpha = -(0.44 \pm 0.04)\times 10^{-16}{\rm y}^{-1}$. 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., Comment: 13 pages including 3 figures; delivered at First Int ASTROD School and Symposium, Sep 13-23, 2001, Beijing, to appear in Int. J. Modern Phys. D, as part of Proceedings. Minor changes in the references

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., Comment: 11 pages including 3 figures. Delivered at The Ninth Workshop on General Relativity and Gravitation, Hiroshima University, Nov. 3--6, 1999: International Seminar Nara 99, Space, Time and Interactions, Nara Women's University, December 4--5, 1999. To appear in Proceedings: Added footnote and references

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 $\Lambda$ 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., Comment: 12 pages LaTex including 1 eps figure

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 $\rho_s$ 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, $\rho_s$ and the ordinary matter density $\rho_m$ 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 $\rho_s$ overtakes $\rho_m$, 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., Comment: 9 pages plus 7 figures

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., Comment: 20 pages LaTex including 6 figures. Theoretical interpretation changed. More detailed discussions on the temperature estimate also added

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., Comment: LaTex, 5 pages, no figures

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., Comment: LaTex, 6 pages, 2 figures

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., Comment: Latex 29 pages, including 9 figures

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., Comment: Latex 12 pages, including 4 eps figures

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.'', Comment: Latex 13 pages, including 3 eps figures

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 $\Lambda$ is not a true constant but decays like $t^{-2}$, thus explaining why any effect of $\Lambda$ 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 $\Lambda$ 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., Comment: uuencoded, gzipped Latex 7 pages including 4 postscript figures using epsf.sty; to appear in Proceedings of RESCEU Symposium "Cosmological Constant and the Evolution of the Universe," 7-10 November 1995, University of Tokyo

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., Comment: 12 pages, latex, 5 figures as epsf files included, compressed uuencoded

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 $\omega$ 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., Comment: 7 pages, LaTex