arXiv subjects

Motohiko Yoshimura

Publications and source records attributed to Motohiko Yoshimura.

At least 19 recordsLinked to original sources

arXiv2026

Control of emission interval and timing in triggered periodic superradiance

To achieve more controllable development of coherence in solids, we investigated the effect of a trigger laser tuned to the superradiance transition wavelength on periodic superradiance observed in an Er:YSO crystal. For period control, applying the trigger laser reduced both the superradiance period and its variance, demonstrating enhanced controllability of coherence development dynamics. As the trigger laser power increased, both the period and the number of emitted superradiance photons decreased while maintaining a proportional relationship. This behavior is explained by a reduced superradiance threshold under a constant excitation rate and is reproduced by numerical simulations based on the Maxwell-Bloch equations. For timing control, we found that superradiance could be triggered even when the excitation laser alone was insufficient. This enabled us to control the emission timing of superradiance using short trigger pulses and provided a device capable of generating superradiance at desired timing.

physics.atom-ph↗

arXiv2025

Observational tests for a class of scalar-tensor gravity

We study observational bounds in a class of scalar-tensor gravity theories recently proposed. Either an upper or lower bound on a conformal factor in these theories is derived from null observation in composition dependent fifth force search, microscope mission. The important case of a lower bound implies that future improved observations have chances of verifying this class of theories. Future prospect for a particular type of observation is mentioned. The considered class of scalar-tensor gravity was shown elsewhere to explain the conversion of inflationary early phase to late time quintessence type dark energy.

astro-ph.CO↗

arXiv2025

A common origin of two accelerating universes: inflation and dark energy

We develop a quantum theory of inflaton and its decay product of various gauge boson pairs to investigate the preheating towards thermalized universe. The inflaton decay into gauge-boson pairs is shown to be inevitably accompanied by tachyon-mass-like correction to inflation potential that ultimately leads to an inflaton escape out of trapped local potential minimum towards the field infinity. This gives rise to a conversion mechanism of early inflationary acceleration to a quintessence dark energy acceleration at late stages of cosmic evolution. The success of the escape depends on how standard particles are incorporated into a scheme of extended Jordan-Brans-Dicke gravity. New types of super-radiance mechanism that enhance the ending of preheating are identified and compared with the Dicke model.

hep-ph↗

arXiv2024

Analytical and numerical studies of periodic superradiance

We conduct a theoretical study to understand the periodic superradiance observed in an Er:YSO crystal. First, we construct a model based on the Maxwell-Bloch equations for a reduced level system, a pair of superradiance states and a population reservoir state. Analysis of the eigenvalues of the linearized differential equations shows that periodic superradiance can be realized only for certain parameters. We also derive two-variable equations consisting of the coherence and population difference between the two superradiance states, which contain the essential feature of the periodic superradiance. The two-variable equations clarify a mathematical structure of this periodic phenomenon and give analytical forms of the period, pulse duration, and number of emitted photons. Our model successfully reproduces the periodic behavior, but the actual experimental parameters are found to be outside the parameter region for the periodic superradiance. This result implies that some other mechanism(s) is required. As one example, assuming that the field decay rate varies with the electric field, the periodic superradiance can be reproduced even under the actual experimental condition.

physics.atom-ph↗

arXiv2024

Parametrically amplified super-radiance towards hot big bang universe

We propose a mechanism of preheating stage after inflation, using a new idea of parametrically amplified super-radiance. Highly coherent state, characterized by macro-coherence of scalar field coupled to produced massless particle in pairs, is created by parametric resonance effects associated with field oscillation around its potential minimum, within a Hubble volume. The state is described effectively by the simple Dicke-type of super-radiance model, and super-radiant pulse is emitted within a Hubble time, justifying neglect of cosmic expansion. Produced particles are shown to interact to change their energy and momentum distribution to realize thermal hot big bang universe. A long standing problem of heating after inflation may thus be solved. A new dark matter candidate produced at the emergence of thermalized universe is suggested as well.

hep-ph↗

arXiv2024

Accelerating universe at early and late times in extended Jordan-Brans-Dicke gravity

We propose a scenario that can explain the early-time inflation and the late-time dark energy within a unified framework. A scalar potential combining power-law and exponential type in a context of extended Jordan-Brans-Dicke gravity is critically important for this realization. A realistic scenario can be achieved in a two-field model in which one directional motion in field space realizes the slow-roll inflation. The inflaton ends up with oscillatory period and turns its direction to another direction that is identified as the quintessence field, giving rise to the dark energy at late times. The inflaton oscillation is expected to realize efficient heating if parametric amplification works. Along the quintessence direction, the present universe is on the way to reach the asymptotic fixed point. We search for successful parameter region, taking potential function in the form of low-order field powers times decreasing exponential in two dimensional field space.

astro-ph.CO↗

arXiv2023

Gravitational and dark wave emission at binary merger

The recently proposed formalism of extended Jordan-Brans-Dicke gravity makes it possible to calculate energy loss rate due to both gravitational wave and scalar field (giving the origin of dark energy) wave emission at merger of a black hole and a neutron star; a binary system of no scalar hair and a star with the scalar charge. The scalar field emission changes orbit parameters of the binary system, thereby changes detectable gravitational wave emission. When neutron stars carry significantly large scalar charge, significant dark wave (namely, scalar field wave) emission occurs at the same time of gravitational wave emission. It is found that solutions of coupled differential equations predict non-vanishing remnant dark charge after the gravitational collapse. This gives two interesting possibilities: (1) the no-hair conjecture of black hole is violated, or (2) a bosonic cloud is formed outside the event horizon of black hole. The bosonic cloud proposed in the literature is a gigantic atom made of gravitationally bound dark energy quanta surrounding a black hole. One can either constrain, or even determine, parameters of extended Jordan-Brans-Dicke gravity from accumulated gravitational wave observations of merging black hole and neutron star.

gr-qc↗

arXiv2023

Periodic super-radiance in Er:YSO crystal

We observed periodic optical pulses from an Er:YSO crystal during irradiating with an continuous-wave excitation laser. We refer to this new phenomenon as "periodic super-radiance". This periodicity can be understood qualitatively by a simple model, in which a cyclic process of a continuous supply of population inversion and a sudden burst of super-radiance is repeated. The excitation power dependences of peak interval and the pulse area can be interpreted with our simple model. In addition, the linewidth of super-radiance is much narrower than an inhomogeneous broadening in a crystal. This result suggests that only Er3+ ions in a specific environment are involved in super-radiance.

physics.atom-ph↗

arXiv2023

Constraints on extended Jordan-Brans-Dicke gravity

Cosmological analysis of extended Jordan-Brans-Dicke (eJBD) gravity is presented in the Einstein metric frame in which gravitational interaction is readily understandable. Our formulation is the first systematic investigation of how to introduce lagrangian of standard particle physics in eJBD framework consistently with the general principle of spontaneously broken gauge symmetry, which makes it possible to confront eJBD-based cosmology with observational and laboratory bounds on time variation of parameters, masses, and coupling constants, caused by time evolution of eJBD fields. Decomposition of standard particle physics lagrangian into independent gauge invariant pieces is proposed to avoid serious conflict that may arise from standard lagrangian transformed from the Jordan frame. Independent conformal factors are assigned to each of five gauge invariant pieces. The formulation is most unambiguously made possible by defining fields having canonical kinetic terms that allow us to use the canonical quantization rule of field theory. This construction gives as one of its consequences the canonical eJBD field $\chi$ that couples to the universal fermion current, a linear combination of baryon and lepton number currents, $\partial_{\mu} \chi (\frac{1}{3} j_B^{\mu} + j_L^{\mu})$, in addition to the conventional trace of the energy-momentum tensor. Field equation of eJBD field along with gravitational equation is analyzed by using a simplified polynomial class of potential and conformal functions, giving time evolution of radiation, matter and dark energy densities consistent with observations when an appropriate set of model parameters are used. Finite temperature corrections are further calculated to give temperature dependent terms in eJBD field potential.

hep-ph↗

arXiv2022

Axion cosmology in the presence of non-trivial Nambu-Goldstone modes

Axion cosmology is reexamined taking into account effect of kinetic pseudo Nambu-Goldstone modes, with its importance recently pointed out. When Peccei-Quinn (PQ) symmetry is broken by a chiral U(1) singlet, it is found that the effect of kinetic Nambu-Goldstone mode makes the axion dark matter untenable. When PQ symmetry is extended and is broken by two singlets, we find axion cosmology to work, but there are several differences from the axion cosmology studied in the literature. The differences are (1) ordinary type of dark matter scaling as $1/{\rm cosmic \; scale\; factor}^3$ arising from a modulus field and not from the usual angular field, (2) mass of the dark matter quantum in the ultralight range, $(10^{-32} \sim 10^{-14})\,$eV, (3) emergence of dark energy with the present density of order (a few meV)$^4$ consistent with observations, (4) presence of a long range spin-dependent force, (5) slow-roll inflation after PQ symmetry breaking when conformal coupling to gravity is introduced.

hep-ph↗

arXiv2019

QED background against atomic neutrino process with initial spatial phase

Atomic deexcitation emitting a neutrino pair and a photon is expected to provide a novel method of neutrino physics if it is enhanced by quantum coherence in a macroscopic target. However, the same enhancement mechanism may also lead to a serious problem of enhanced QED background process. We show that the QED background can be suppressed enough in the photonic crystal waveguide by using the spatial phase that is imprinted in the process of initial coherence generation in the target at excitation.

hep-ph↗

arXiv2019

Testing unitarity of the $3\times 3$ neutrino mixing matrix in an atomic system

Unitarity of the $3\times 3$ lepton flavor mixing matrix $V$ is unavoidably violated in a seesaw mechanism if its new heavy degrees of freedom are slightly mixed with the active neutrino flavors. We propose to use the atomic transition process ${\left| \rm e \right> \to\left|\rm g \right> + γ+ ν^{}_{i} + \overlineν^{}_{j}}$ (for $i, j = 1, 2, 3$), where $\left|\rm e \right>$ and $\left|\rm g \right>$ stand respectively for the excited and ground levels of an atomic system, to probe or constrain the unitarity-violating effects of $V$. We find that the photon spectrum of this transition will be distorted by the effects of $V V^\dagger \neq {\bf 1}$ and $V^\dagger V \neq {\bf 1}$ as compared with the $V V^\dagger = V^\dagger V = {\bf 1}$ case. We locate certain frequencies in the photon spectrum to minimize the degeneracy of effects of the unitarity violation and uncertainties of the flavor mixing parameters themselves. The requirements of a nominal experimental setup to test the unitarity of $V$ are briefly discussed.

hep-ph↗

arXiv2019

X-ray pumping of the Th-229 nuclear clock isomer

Thorium-229 is a unique case in nuclear physics: it presents a metastable first excited state Th-229m, just a few electronvolts above the nuclear ground state. This so-called isomer is accessible by VUV lasers, which allows transferring the amazing precision of atomic laser spectroscopy to nuclear physics. Being able to manipulate the Th-229 nuclear states at will opens up a multitude of prospects, from studies of the fundamental interactions in physics to applications as a compact and robust nuclear clock. However, direct optical excitation of the isomer or its radiative decay back to the ground state has not yet been observed, and a series of key nuclear structure parameters such as the exact energies and half-lives of the low-lying nuclear levels of Th-229 are yet unknown. Here we present the first active optical pumping into Th-229m. Our scheme employs narrow-band 29 keV synchrotron radiation to resonantly excite the second excited state, which then predominantly decays into the isomer. We determine the resonance energy with 0.07 eV accuracy, measure a half-life of 82.2 ps, an excitation linewidth of 1.70 neV, and extract the branching ratio of the second excited state into the ground and isomeric state respectively. These measurements allow us to re-evaluate gamma spectroscopy data that have been collected over 40~years.

nucl-ex↗

arXiv2019

Coherent two-photon emission from hydrogen molecules excited by counter-propagating laser pulses

We observed two-photon emission signals from the first vibrationally excited state of parahydrogen gas excited coherently by counter-propagating laser pulses. A single narrow-linewidth laser source was used to excite the parahydrogen molecules and induce the two-photon emission process. We measured how the signal energy depended on the detuning, target gas pressure, and input pulse energies. These results are qualitatively consistent with those obtained by numerical simulations based on the Maxwell-Bloch equations with one spatial dimension and one temporal dimension. This study of two-photon emission with counter-propagating injection is an important step toward neutrino mass spectroscopy.

physics.atom-ph↗

arXiv2018

Geometry-dependent spectra and coherent-transient measurement of nearly degenerate four-wave mixing using two-photon resonance

We study nearly degenerate four-wave mixing using a two-photon-allowed vibrational transition of parahydrogen. A signal photon is generated by a trigger photon and coherence among parahydrogen, which is prepared by two counterpropagating pump pulses. The dependence of the signal pulse energy on the trigger frequency are investigated. The measured spectra vary depending on the geometry. They shift depending on the direction of the signal pulse and on the small angle formed by the counterpropagating pump pulses. Furthermore, the dependence of signal pulse energy on the incident time of the trigger pulse is investigated. The measured signal pulse energy is high if the trigger pulse is slightly delayed with respect to the pump pulses. We demonstrate that these geometry-dependent spectra and coherent-transient response can be explained by using simple models.

physics.atom-ph↗

arXiv2018

Tomography by neutrino pair beam

We consider tomography of the Earth's interior using the neutrino pair beam which has recently been proposed. The beam produces a large amount of neutrino and antineutrino pairs from the circulating partially stripped ions and provides the possibility to measure precisely the energy spectrum of neutrino oscillation probability together with a sufficiently large detector. It is shown that the pair beam gives a better sensitivity to probe the Earth's crust compared with the neutrino sources at present. In addition we present a method to reconstruct a matter density profile by means of the analytic formula of the oscillation probability in which the matter effect is included perturbatively to the second order.

hep-ph↗

arXiv2017

Effects of initial spatial phase in radiative neutrino pair emission

We study radiative neutrino pair emission in deexcitation process of atoms taking into account coherence effect in a macroscopic target system. In the course of preparing the coherent initial state to enhance the rate, a spatial phase factor is imprinted in the macroscopic target. It is shown that this initial spatial phase changes the kinematics of the radiative neutrino pair emission. We investigate effects of the initial spatial phase in the photon spectrum of the process. It turns out that the initial spatial phase provides us significant improvements in exploring neutrino physics such as the Dirac-Majorana distinction and the cosmic neutrino background.

hep-ph↗

arXiv2017

Towards Background-free RENP using a Photonic Crystal Waveguide

We study how to suppress multiphoton emission background in QED against radiative emission of neutrino pair (RENP) from atoms. We purse the possibility of background suppression using the photonic band structure of periodic dielectric media, called photonic crystals. The modification of photon emission rate in photonic crystal waveguides is quantitatively examined to clarify the condition of background-free RENP.

physics.optics↗