KINDAI UNIVERSITY


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TARO INOUE Kaiki

Profile

FacultyDepartment of Science / Graduate School of Science and Engineering Research
PositionProfessor
DegreePhD
Commentator Guidehttps://www.kindai.ac.jp/meikan/272-inoue-kaiki.html
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Last Updated :2020/04/03

Education and Career

Education

  •   1992 04  - 1995 06 , International Christian University, Department of Liberal Arts
  •   1996 04  - 2001 03 , Kyoto University, Graduate School of Science

Academic & Professional Experience

  •   2019 04 ,  - 現在, Professor, Kindai University
  •   2007 04 ,  - 2019 03 , Associate Professor, Department of Science and Engineering, Kinki University
  •   2004 04 ,  - 2006 03 , Lecturer, Department of Science and Engineering, Kinki University

Research Activities

Research Areas

  • Natural sciences, Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics
  • Natural sciences, Astronomy

Research Interests

  • gravitational lensing, cosmic microwave background, cosmology, astrophysics, gravitational wave, cosmic topology, radio astronomy, dark matter

Published Papers

  • Environmental effects on halo abundance and weak lensing peak statistics toward large underdense regions, Yuichi Higuchi, Kaiki Taro Inoue, Aug. 2019
    Summary:The cosmic microwave background (CMB) contains an anomalous cold spot with a
    surrounding hot ring, known as the Cold Spot. Inoue & Silk (2006) proposed that
    this feature could be explained by postulating a supervoid: if such a large
    underdense region exists, then the growth of matter perturbing around the spot
    might differ from the average value in the Universe and the differences might
    affect weak lensing analysis of peak statistics. To investigate environmental
    effects on halo number count and peak statistics, we used a publicly available
    ray-tracing simulation for a box size of 2250$h^{-1}$Mpc on a side (Takahashi
    et al. 2017). We found that the number counts for massive haloes toward the
    largest underdense region in the simulation decreases and the corresponding
    significance of the difference, based on a cosmic average, is $\geq3\sigma$. On
    the basis of the results of peak statistics analysis, the number of high peaks
    decreases with the decrement of massive haloes, but the number of low peaks
    increases with the lack of matter in the line of sight. The highest
    significance of the decrement in peak counts in large underdense regions is
    $5\sigma$ in the total signal-to-noise ratio. Our result implies that
    environmental effects on halo abundance and weak lensing peak statistic can be
    used to probe the presence and properties of supervoids.
  • Probing supervoids with weak lensing, Yuichi Higuchi, Kaiki Taro Inoue, Jan. 2018
    Summary:The cosmic microwave background (CMB) has non-Gaussian features in the
    temperature fluctuations. An anomalous cold spot surrounded with a hot ring,
    called the Cold Spot is one of such features. If a large underdence region
    (supervoid) resides towards the Cold Spot, we would be able to detect a
    systematic shape distortion in the images of background source galaxies via
    weak lensing effect. In order to estimate the detectability of such signals, we
    used the data of $N$-body simulations to simulate full-sky ray-tracing of
    source galaxies. We searched for a most prominent underdense region using the
    simulated convergence maps smoothed at a scale of 20 degree and obtained
    tangential shears around it. The lensing signal expected in a concordant
    $\Lambda$CDM model can be detected at a signal-to-noise ratio $S/N\sim3$. If a
    supervoid with a radius of $\sim 200\,h^{-1}\,\textrm{Mpc}$ and a density
    contrast $\delta_0 \sim -0.3$ at the centre resides at a redshift $z\sim 0.2$,
    on-going and near-future weak gravitational lensing surveys would detect a
    lensing signal with $S/N\gtrsim4$ without resorting to stacking. From the
    tangential shear profile, we can obtain a constraint on the projected mass
    distribution of the supervoid.
  • Constraints on long-lived electrically charged massive particles from anomalous strong lens systems, Ayuki Kamada, Kaiki Taro Inoue, Kazunori Kohri, Tomo Takahashi, Nov. 2017
    Summary:We investigate anomalous strong lens systems, particularly the effects of
    weak lensing by structures in the line of sight, in models with long-lived
    electrically charged massive particles (CHAMPs). In such models, matter density
    perturbations are suppressed through the acoustic damping and the flux ratio of
    lens systems are impacted, from which we can constrain the nature of CHAMPs.
    For this purpose, first we perform $N$-body simulations and develop a fitting
    formula to obtain non-linear matter power spectra in models where cold neutral
    dark matter and CHAMPs coexist in the early Universe. By using the observed
    anomalous quadruple lens samples, we obtained the constraints on the lifetime
    ($\tau_{\rm Ch}$) and the mass density fraction ($r_{\rm Ch}$) of CHAMPs. We
    show that, for $r_{\rm Ch}=1$, the lifetime is bounded as $\tau_{\rm Ch} <
    0.96\,$yr (95% confidence level), while a longer lifetime $\tau_{\rm Ch} =
    10\,$yr is allowed when $r_{\rm Ch} < 0.5$ at the 95% confidence level.
    Implications of our result for particle physics models are also discussed.
  • Probing Dark Dwarf Galaxy and Dark Matter with ALMA, 井上 開輝, 天文月報 = The astronomical herald, 天文月報 = The astronomical herald, 110(5), 341 - 349, May 2017
  • Probing Dark Dwarf Galaxy and Dark Matter with ALMA, 井上開輝, 天文月報, 天文月報, 110(5), 341‐349, Apr. 20 2017
  • Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG0414+0534, Kaiki Taro Inoue, Satoki Matsushita, Takeo Minezaki, Masashi Chiba, The Astrophysical Journal Letters (2017), 835, Number 2, L23 (published on Jan. 30), The Astrophysical Journal Letters (2017), 835, Number 2, L23 (published on Jan. 30), Jan. 19 2017
    Summary:We report the $4 \, \sigma$ detection of a faint object with a flux of ~ 0.3
    mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama
    Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably
    a dusty dark dwarf galaxy, which has not been detected in either the optical,
    near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the
    lensed images observed in Band 7 and the mid-infrared (MIR) band and the
    reddening of the QSO light color can be simultaneously explained if we consider
    the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of
    $0.5 \lesssim z \lesssim 1$. Using the best-fit lens models with three lenses,
    we find that the dark matter plus baryon mass associated with the object is
    $\sim 10^9\, M_{\odot}$, the dust mass is $\sim 10^7\,M_{\odot}$ and the linear
    size is $\gtrsim 5\,$kpc. Thus our findings suggest that the object is a dusty
    dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs)
    in the universe may be attributed to such dark objects.
  • Detecting Sub-lunar Mass Compact Objects toward the Local Group Galaxies, Kaiki Taro Inoue, Sep. 15 2016
    Summary:By monitoring a large number of stars in the Local Group galaxies, we can
    detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as
    primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the
    Milky Way halo. In contarst to microlensing by stellar-mass objects, the
    finite-source size effect becomes important and the lensing time duration
    becomes shorter ($\sim 10^{1-4}\,\textrm{s}$). Using stars with $V<26$ in M33
    as sources, for one-night observation, we would be able to detect $10^{3-4}$
    nanolensing events caused by SULCOs in the Milky Way halo with a mass of
    $10^{-9}M_{\odot}$ to $10^{-7}M_{\odot}$ for sources with S/N$>5$ if SULCOs
    constitute all the dark matter components. Moreover, we expect $10^{1-2}$
    events in which bright blue stars with S/N$>100$ are weakly amplified due to
    lensing by SULCOs with a mass range of $10^{-11}M_{\odot}$ to
    $10^{-9}M_{\odot}$. Thus the method would open a new window on SULCOs in the
    Milky Way halo that would otherwise not be observable.
  • Constraints on mixed dark matter from anomalous strong lens systems, KAMADA Ayuki, INOUE Kaiki Taro, TAKAHASHI Tomo, Physical Review. D. Covering Particles, Fields, Gravitation, and Cosmology, Physical Review. D. Covering Particles, Fields, Gravitation, and Cosmology, 94(2,Pt.A), 023522.1‐023522.10, Jul. 2016
    Summary:Recently it has been claimed that the warm dark matter (WDM) model cannot at
    the same time reproduce the observed Lyman-{\alpha} forests in distant quasar
    spectra and solve the small-scale issues in the cold dark matter (CDM) model.
    As an alternative candidate, it was shown that the mixed dark matter (MDM)
    model that consists of WDM and CDM can satisfy the constraint from
    Lyman-{\alpha} forests and account for the "missing satellite problem" as well
    as the reported 3.5 keV anomalous X-ray line. We investigate observational
    constraints on the MDM model using strong gravitational lenses. We first
    develop a fitting formula for the nonlinear power spectra in the MDM model by
    performing N-body simulations and estimate the expected perturbations caused by
    line-of-sight structures in four quadruply lensed quasars that show anomaly in
    the flux ratios. Our analysis indicates that the MDM model is compatible with
    the observed anomaly if the mass fraction of the warm component is smaller than
    0.47 at the 95% confidence level. The MDM explanation to the anomalous X-ray
    line and the small-scale issues is still viable even after this constraint is
    taken into account.
  • ALMA Imprint of Intergalactic Dark Structures in the Gravitational Lens SDP.81, Kaiki Taro Inoue, Takeo Minezaki, Satoki Matsushita, Masashi Chiba, MNRAS (April 11, 2016) Vol. 457 2936-2950 First published online February 17, 2016, MNRAS (April 11, 2016) Vol. 457 2936-2950 First published online February 17, 2016, Oct. 01 2015
    Summary:We present an analysis of the ALMA long baseline science verification data of
    the gravitational lens system SDP.81. We fit the positions of the brightest
    clumps at redshift z=3.042 and a possible AGN component of the lensing galaxy
    at redshift z=0.2999 in the band 7 continuum image using a canonical lens
    model, a singular isothermal ellipsoid plus an external shear. Then, we measure
    the ratio of fluxes in some apertures at the source plane where the lensed
    images are inversely mapped. We find that the aperture flux ratios of band 7
    continuum image are perturbed by 10-20 percent with a significance at 2 ~ 3
    sigma level. Moreover, we measure the astrometric shifts of multiply lensed
    images near the caustic using the CO(8-7) line. Using a lens model best-fitted
    to the band 7 continuum image, we reconstruct the source image of the CO(8-7)
    line by taking linear combination of inverted quadruply lensed images. At the
    50th channel (rest-frame velocity 28.6 km/s) of the CO(8-7) line, we find an
    imprint of astrometric shifts of the order of 0.01 arcsec in the source image.
    Based on a semi-analytic calculation, we find that the observed anomalous flux
    ratios and the astrometric shifts can be explained by intergalactic dark
    structures in the line of sight. A compensated homogeneous spherical clump with
    a mean surface mass density of the order of 10^8 solar mass h^-1 arcsec^-2 can
    explain the observed anomaly and astrometric shifts simultaneously.
  • Weak Lensing by Minifilament or Minivoid as the Origin of Flux-ratio Anomalies in Lensed Quasar MG0414+0534, Kaiki Taro Inoue, Oct. 04 2014
    Summary:We explore the weak lensing effects by ministructures in the line-of-sight in
    a quadruply lensed quasar MG0414+0534 that shows an anomaly in the flux-ratios.
    We find that the observed flux-ratio anomaly can be explained by a presence of
    either a minifilament or a minivoid in the line-of-sight with a surface mass
    density of the order of 10^(8-9) h^(-1) solar mass /arcsec^2 without taking
    into account any subhalos in the lensing galaxy. The astrometric perturbation
    by a possible minifilament/minivoid is <~ 0.001 arcsec and the amplitudes of
    convergence perturbations due to these perturbers are ~ 0.004-0.008 at the
    place of an image that shows anomaly. In order to discriminate models with the
    line-of-sight ministructures from those with a subhalo(s) in the lensing
    galaxy, we need to precisely measure the projected convergence and shear around
    the lensing galaxy. The differential magnification effect could break the model
    degeneracy if the source size is > ~100 pc. Observation at the submillimeter
    band using interferometers will enable us to determine the origin of anomalies
    in the flux ratios.
  • Weak Lensing by Minifilament or Minivoid as the Origin of Flux-ratio Anomalies in Lensed Quasar MG0414+0534, Kaiki Taro Inoue, MNRAS, Vol. 447, Issue 2, p.1452-1459 (2015), MNRAS, Vol. 447, Issue 2, p.1452-1459 (2015), Oct. 04 2014
    Summary:We explore the weak lensing effects by ministructures in the line-of-sight in
    a quadruply lensed quasar MG0414+0534 that shows an anomaly in the flux-ratios.
    We find that the observed flux-ratio anomaly can be explained by a presence of
    either a minifilament or a minivoid in the line-of-sight with a surface mass
    density of the order of 10^(8-9) h^(-1) solar mass /arcsec^2 without taking
    into account any subhalos in the lensing galaxy. The astrometric perturbation
    by a possible minifilament/minivoid is <~ 0.001 arcsec and the amplitudes of
    convergence perturbations due to these perturbers are ~ 0.004-0.008 at the
    place of an image that shows anomaly. In order to discriminate models with the
    line-of-sight ministructures from those with a subhalo(s) in the lensing
    galaxy, we need to precisely measure the projected convergence and shear around
    the lensing galaxy. The differential magnification effect could break the model
    degeneracy if the source size is > ~100 pc. Observation at the submillimeter
    band using interferometers will enable us to determine the origin of anomalies
    in the flux ratios.
  • Constraints on warm dark matter from weak lensing in anomalous quadruple lenses, Kaiki Taro Inoue, Ryuichi Takahashi, Tomo Takahashi, Tomoaki Ishiyama, Sep. 04 2014
    Summary:We investigate the weak lensing effect by line-of-sight structures with a
    surface mass density of <~10^8 solar mass/arcsec^2 in QSO-galaxy quadruple lens
    systems. Using high-resolution N-body simulations in warm dark matter (WDM)
    models and observed four quadruple lenses that show anomalies in the flux
    ratios, we obtain constraints on the mass of thermal WDM, m_WDM>=
    1.3keV(95%CL), which is consistent with those from Lyman-$\alpha$ forests and
    the number counts of high-redshift galaxies at z>4. Our results show that WDM
    with a free-streaming comoving wavenumber k_{fs} <= 27 h/Mpc is disfavored as
    the major component of cosmological density at redshifts 0.5 <~ z <~ 4.
  • Constraints on warm dark matter from weak lensing in anomalous quadruple lenses, Kaiki Taro Inoue, Ryuichi Takahashi, Tomo Takahashi, Tomoaki Ishiyama, MNRAS (April 11, 2015) 448 (3): 2704-2716. First published online March 9, 2015, MNRAS (April 11, 2015) 448 (3): 2704-2716. First published online March 9, 2015, Sep. 04 2014
    Summary:We investigate the weak lensing effect by line-of-sight structures with a
    surface mass density of <~10^8 solar mass/arcsec^2 in QSO-galaxy quadruple lens
    systems. Using high-resolution N-body simulations in warm dark matter (WDM)
    models and observed four quadruple lenses that show anomalies in the flux
    ratios, we obtain constraints on the mass of thermal WDM, m_WDM>= 1.3keV(95%CL)
    assuming that the density of the primary lens is described by a singular
    isothermal ellipsoid (SIE). The obtained constraint is consistent with those
    from Lyman-$\alpha$ forests and the number counts of high-redshift galaxies at
    z>4. Our results show that WDM with a free-streaming comoving wavenumber k_{fs}
    <= 27 h/Mpc is disfavored as the major component of cosmological density at
    redshifts 0.5 <~ z <~ 4 provided that the SIE models describe the gravitational
    potentials of the primary lenses correctly.
  • Weak lensing by intergalactic ministructures in quadruple lens systems: simulation and detection, TAKAHASHI Ryuichi, INOUE Kaiki Taro, Mon Not R Astron Soc, Mon Not R Astron Soc, 440(1), 870 - 888, May 01 2014
    Summary:We investigate the weak lensing effects of line-of-sight structures on
    quadruple images in quasar-galaxy strong lens systems based on N-body and
    ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass.
    The intervening halos and voids disturb the magnification ratios of lensed
    images as well as their relative positions due to lensing. The magnification
    ratios typically change by O(10%) when the shifts of relative angular positions
    of lensed images are constrained to <0.004 arcsec. The constrained amplitudes
    of projected density perturbations due to line-of-sight structures are O(10^8)
    solar mass per arcsec^2. These results are consistent with our new analytical
    estimate based on the two-point correlation of density fluctuations. The
    observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with
    quadruple images agree well with the numerically estimated values without
    taking into account of subhalos residing in the lensing galaxies. We find that
    the constrained mean amplitudes of projected density perturbations in the
    line-of-sight are negative, which suggests that the fluxes of lensed images are
    perturbed mainly by minivoids and minihalos in underdense regions. We derive a
    new fitting formula for estimating the probability distribution function of
    magnification perturbation. We also find that the mean amplitude of
    magnification perturbation roughly equals the standard deviation regardless of
    the model parameters.
  • Weak Lensing by Intergalactic Mini-Structures in Quadruple Lens Systems: Simulation and Detection, Ryuichi Takahashi, Kaiki Taro Inoue, Aug. 22 2013
    Summary:We investigate the weak lensing effects of line-of-sight structures on
    quadruple images in quasar-galaxy strong lens systems based on N-body and
    ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass.
    The intervening halos and voids disturb the magnification ratios of lensed
    images as well as their relative positions due to lensing. The magnification
    ratios typically change by O(10%) when the shifts of relative angular positions
    of lensed images are constrained to <0.004 arcsec. The constrained amplitudes
    of projected density perturbations due to line-of-sight structures are O(10^8)
    solar mass per arcsec^2. These results are consistent with our new analytical
    estimate based on the two-point correlation of density fluctuations. The
    observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with
    quadruple images agree well with the numerically estimated values without
    taking into account of subhalos residing in the lensing galaxies. We find that
    the constrained mean amplitudes of projected density perturbations in the
    line-of-sight are negative, which suggests that the fluxes of lensed images are
    perturbed mainly by minivoids and minihalos in underdense regions. We derive a
    new fitting formula for estimating the probability distribution function of
    magnification perturbation. We also find that the mean amplitude of
    magnification perturbation roughly equals the standard deviation regardless of
    the model parameters.
  • Reconstruction of Missing Data in the Sky using Iterative Harmonic Expansion, Atsushi J. Nishizawa, Kaiki Taro Inoue, May 01 2013
    Summary:Missing fluctuations in masked regions in the sky can be reconstructed from
    fluctuations in the surrounding unmasked regions if they are sufficiently
    smooth. We propose to reconstruct such missing fluctuations by iteratively
    applying a spherical harmonic expansion to fluctuations in the unmasked region.
    The accuracy of reconstruction depends on the mask geometries, the spectrum of
    underlying density fluctuations, and the number of iterations. For Gaussian
    fluctuations with the Harrison-Zel'dovich spectrum, our method provides more
    accurate restoration than naive methods using the brute-forth matrix inversion
    or the singular value decomposition.
  • Reconstruction of Missing Data using Iterative Harmonic Expansion, Atsushi J. Nishizawa, Kaiki Taro Inoue, MNRAS (October 11, 2016) 462 (1): 588-600, MNRAS (October 11, 2016) 462 (1): 588-600, May 01 2013
    Summary:In the cosmic microwave background or galaxy density maps, missing
    fluctuations in masked regions can be reconstructed from fluctuations in the
    surrounding unmasked regions if the original fluctuations are sufficiently
    smooth. One reconstruction method involves applying a harmonic expansion
    iteratively to fluctuations in the unmasked region. In this paper, we discuss
    how well this reconstruction method can recover the original fluctuations
    depending on the prior of fluctuations and property of the masked region. The
    reconstruction method is formulated with an asymptotic expansion in terms of
    the size of mask for a fixed iteration number. The reconstruction accuracy
    depends on the mask size, the spectrum of the underlying density fluctuations,
    the scales of the fluctuations to be reconstructed and the number of
    iterations. For Gaussian fluctuations with the Harrison--Zel'dovich spectrum,
    the reconstruction method provides more accurate restoration than naive methods
    based on brute--forth matrix inversion or the singular value decomposition. We
    also demonstrate that an isotropic non-Gaussian prior does not change the
    results but an anisotropic non-Gaussian prior can yield a higher reconstruction
    accuracy compared to the Gaussian prior case.
  • Direct Gravitational Imaging of Intermediate Mass Black Holes in Extragalactic Halos, Kaiki Taro Inoue, Valery Rashkov, Joseph Silk, Piero Madau, MNRAS (November 01, 2013) 435 (3): 2092-2098, MNRAS (November 01, 2013) 435 (3): 2092-2098, 435(3), 2092 - 2098, Jan. 22 2013
    Summary:A galaxy halo may contain a large number of intermediate mass black holes
    (IMBHs) with masses in the range of 10^{2-6} solar mass. We propose to directly
    detect these IMBHs by observing multiply imaged QSO-galaxy or galaxy-galaxy
    strong lens systems in the submillimeter bands with high angular resolution.
    The silhouette of an IMBH in the lensing galaxy halo would appear as either a
    monopole-like or a dipole-like variation at the scale of the Einstein radius
    against the Einstein ring of the dust-emitting region surrounding the QSO. We
    use a particle tagging technique to dynamically populate a Milky Way-sized dark
    matter halo with black holes, and show that the surface mass density and number
    density of IMBHs have power-law dependences on the distance from the center of
    the host halo if smoothed on a scale of ~ 1 kpc. Most of the black holes
    orbiting close to the center are freely roaming as they have lost their dark
    matter hosts during infall due to tidal stripping. Next generation
    submillimeter telescopes with high angular resolution (< 0.3 mas) will be
    capable of directly mapping such off-nuclear freely roaming IMBHs with a mass
    of ~ 10^6 solar mass in a lensing galaxy that harbours a O(10^9) solar mass
    supermassive black hole in its nucleus.
  • Weak Lensing by Line-of-sight Halos as the Origin of Flux-ratio Anomalies in Quadruply Lensed QSOs, Kaiki Taro Inoue, Ryuichi Takahashi, MNRAS 426, 2978-2993 (2012), MNRAS 426, 2978-2993 (2012), Jul. 10 2012
    Summary:We explore the weak lensing effect by line-of-sight halos and sub-halos with
    a mass of M < 10^7 solar mass in QSO-galaxy strong lens systems with quadruple
    images in a concordant LCDM universe. Using a polynomially fitted non-linear
    power spectrum P(k) obtained from N-body simulations that can resolve halos
    with a mass of M ~ 10^5 solar mass, or structures with a comoving wavenumber of
    k ~ 3*10^2 h/Mpc, we find that the ratio of magnification perturbation due to
    intervening halos to that of a primary lens is typically ~10 per cent and the
    predicted values agree well with the estimated values for 6 observed QSO-galaxy
    lens systems with quadruple images in the mid-infrared band without considering
    the effects of substructures inside a primary lens. We also find that the
    estimated amplitudes of convergence perturbation for the 6 lenses increase with
    the source redshift as predicted by theoretical models. Using an extrapolated
    matter power spectrum, we demonstrate that small halos or sub-halos in the
    line-of-sight with a mass of M=10^3-10^7 solar mass, or structures with a
    comoving wavenumber of k=3*10^2-10^4 h/Mpc can significantly affect the
    magnification ratios of the lensed images. Flux ratio anomalies in QSO-galaxy
    strong lens systems offer us a unique probe into clustering property of
    mini-halos with a mass of M < 10^6 solar mass.
  • On the origin of the Cold Spot, Kaiki Taro Inoue, MNRAS, 421, p2731-2736 (2012), MNRAS, 421, p2731-2736 (2012), Sep. 21 2011
    Summary:In a concordant $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, large-angle
    Cosmic Microwave Background (CMB) temperature anisotropy due to linear
    perturbations in the local universe is not negligible. We explore a possible
    role of an underdense region (void) that may cause an anomalous Cold Spot (CS)
    in the CMB sky. Although the observed anomalous cold region with a surrounding
    hot ring can be produced by an underdense region surrounded by a massive wall,
    a decrement in the CMB temperature in the line-of-sight is suppressed because
    of blueshift of CMB photons that pass the wall. Therefore, undercompensated
    models give better agreement with the observed data in comparison with
    overcompensated or compensated models. We find that it is likely that $\sim$90
    per cent of the CMB fluctuation is generated due to an overdense region
    surrounded by an underdense region at the last scattering surface, and the
    remaining $\sim 10$ per cent is produced due to a single spherical underdense
    region with a radius $r\sim 6\times 10^2 h^{-1}$Mpc and a density contrast
    $\delta_m\sim -0.009$ ($2 \sigma$) at redshift $z\sim 1$ in the line-of-sight
    to the CS. The probability of chance alignment of such two structures is $\sim
    0.7$ per cent if the perturbation with an underdense region at $z\sim 1$ is
    moderately undercompensated.
  • Evidence of Quasi-linear Super-Structures in the Cosmic Microwave Background and Galaxy Distribution, Kaiki Taro Inoue, Nobuyuki Sakai, Kenji Tomita, Astrophys. J., 724, p12-25 (2010), Astrophys. J., 724, p12-25 (2010), May 24 2010
    Summary:Recent measurements of hot and cold spots on the cosmic microwave background
    (CMB) sky suggest a presence of super-structures on (>100 h^{-1}Mpc) scales. We
    develop a new formalism to estimate the expected amplitude of temperature
    fluctuations due to the integrated Sachs-Wolfe (ISW) effect from prominent
    quasi-linear structures. Applying the developed tools to the observed ISW
    signals from voids and clusters in catalogs of galaxies at redshifts z<1, we
    find that they indeed imply a presence of quasi-linear super-structures with a
    comoving radius 100~300 h^{-1}Mpc and a density contrast ~O(0.1). We find that
    the observed ISW signals are at odd with the concordant \Lambda cold dark
    matter (CDM) model that predicts Gaussian primordial perturbations at equal to
    or larger than 3 sigma level. We also confirm that the mean temperature around
    the CMB cold spot in the southern Galactic hemisphere filtered by a
    compensating top-hat filter deviates from a mean value at ~3 sigma level,
    implying that a quasi-linear supervoid or an underdensity region surrounded by
    a massive wall may reside at low redshifts z<0.3 and the actual angular size
    (16^\circ-17^\circ) may be larger than the apparent size (4^\circ-10^\circ)
    discussed in literature. Possible solutions are briefly discussed.
  • Subaru Mid-infrared Imaging of the Quadruple Lenses. II. Unveiling Lens Structure of MG0414+0534 and Q2237+030, Takeo Minezaki, Masashi Chiba, Nobunari Kashikawa, Kaiki Taro Inoue, Hirokazu Kataza, Astrophys.J.697:610-618,2009, Astrophys.J.697:610-618,2009, Mar. 14 2009
    Summary:We present mid-infrared imaging at 11.7 $\mu$m for the quadruple lens
    systems, MG0414+0534 and Q2237+030, using the cooled mid-infrared camera and
    spectrometer (COMICS) attached on the Subaru telescope. MG0414+0534 is
    characterized by a bright pair of lensed images (A1, A2) and their optical flux
    ratio A2/A1 deviates significantly from the prediction of a smooth lens model.
    Q2237+030 is comprised of four lensed images, which are significantly affected
    by microlensing in a foreground lensing galaxy. Our mid-infrared observations
    of these lensed images have revealed that the mid-infrared flux ratio for A2/A1
    of MG0414+0534 is nearly unity (0.90 +- 0.04). We find that this flux ratio is
    systematically small, at 4 to 5 sigma level, compared with the prediction of a
    best smooth lens model (1.09) represented by a singular isothermal ellipsoid
    and external shear, thereby suggesting the presence of substructures to explain
    our observational result. In contrast, for Q2237+030, our high signal-to-noise
    observation indicates that the mid-infrared flux ratios between all the four
    images of Q2237+030 are virtually consistent with the prediction of a smooth
    lens model. Based on the size estimate of the dust torus surrounding the nuclei
    of these QSOs, we set limits on the mass of a substructure in these lens
    systems, which can cause anomalies in the flux ratios. For MG0414+0534, since
    the required mass of a substructure inside its Einstein radius is > 360 M_sun,
    millilensing by a CDM substructure is most likely. If it is modeled as a
    singular isothermal sphere, the mass inside radius of 100 pc is given as >
    1.0x10^5 M_sun. For Q2237+030, there is no significant evidence of
    millilensing, so the reported anomalous flux ratios in shorter wavelengths are
    entirely caused by microlensing by stars (abridged).
  • Probing violation of the Copernican principle via the integrated Sachs-Wolfe effect, Kenji Tomita, Kaiki Taro Inoue, Phys.Rev.D79:103505,2009, Phys.Rev.D79:103505,2009, Mar. 09 2009
    Summary:Recent observational data of supernovae indicate that we may live in an
    underdense region, which challenges the Copernican principle. We show that the
    integrated Sachs-Wolfe (ISW) effect is an excellent discriminator between
    anti-Copernican inhomogeneous models and the standard Copernican models. As a
    reference model, we consider an anti-Copernican inhomogeneous model that
    consists of two inner negatively curved underdense regions and an outer flat
    Einstein-de Sitter region. We assume that these regions are connected by two
    thin-walls at redshifts z = 0.067 and z=0.45. In the inner two regions, the
    first-order ISW effect is dominant and comparable to that in the concordant
    flat-Lambda models. In the outer Einstein-de Sitter region, the first-order ISW
    effect vanishes but the second-order ISW effect plays a dominant role, while
    the first-order ISW effect is dominant in the flat-Lambda models at moderate
    redshifts. This difference can discrimate the anti-Copernican models from the
    concordant flat-Lambda model. At high redshits, the second-order ISW effect is
    dominant both in our inhomogeneous model and the concordant model. In the outer
    region, moreover, the ISW effect due to large-scale density perturbations with
    a present matter density contrast much less than 0.37 is negligible, while the
    effect due to small-scale density perturbations (such as clusters of galaxies,
    superclusters and voids) with matter density contrast much larger than 0.37
    would generate anisotropies which are larger than those generated by the ISW
    effect in the concordant model.
  • Cosmic Microwave Background Anisotropy from Nonlinear Structures in Accelerating Universes, Nobuyuki Sakai, Kaiki Taro Inoue, Phys.Rev.D78:063510,2008, Phys.Rev.D78:063510,2008, May 22 2008
    Summary:We study the cosmic microwave background (CMB) anisotropy due to spherically
    symmetric nonlinear structures in flat universes with dust and a cosmological
    constant. By modeling a time-evolving spherical compensated void/lump by
    Lemaitre-Tolman-Bondi spacetimes, we numerically solve the null geodesic
    equations with the Einstein equations. We find that a nonlinear void redshifts
    the CMB photons that pass through it regardless of the distance to it. In
    contrast, a nonlinear lump blueshifts (or redshifts) the CMB photons if it is
    located near (or sufficiently far from) us. The present analysis
    comprehensively covers previous works based on a thin-shell approximation and a
    linear/second order perturbation method and the effects of shell thickness and
    full nonlinearity. Our results indicate that, if quasi-linear and large
    ($>100$Mpc) voids/lumps would exist, they could be observed as cold or hot
    spots with temperature variance $>10^{-5}$K in the CMB sky.
  • Harmonic Inpainting of the Cosmic Microwave Background Sky: Formulation and Error Estimate, Kaiki Taro Inoue, Paolo Cabella, Eiichiro Komatsu, Phys.Rev.D77:123539,2008, Phys.Rev.D77:123539,2008, Apr. 03 2008
    Summary:We develop a new interpolation scheme, based on harmonic inpainting, for
    reconstructing the cosmic microwave background temperature data within the
    Galaxy mask from the data outside the mask. We find that, for scale-invariant
    isotropic random Gaussian fluctuations, the developed algorithm reduces the
    errors in the reconstructed map for the odd-parity modes significantly for
    azimuthally symmetric masks with constant galactic latitudes. For a more
    realistic Galaxy mask, we find a modest improvement in the even-parity modes as
    well.
  • Lens Mapping of Dark Matter Substructure with VSOP-2, Shigenori Ohashi, Masashi Chiba, Kaiki Taro Inoue, Feb. 13 2008
    Summary:Hierarchical clustering models of cold dark matter (CDM) predict that about
    5% - 10% of a galaxy-sized halo with mass ~ 10^12 solar masses (M_sun) resides
    in substructures (CDM subhalos) with masses <= 10^8 M_sun. To directly identify
    such substructures, we propose to observe radio continuum emission from
    multiply imaged QSOs using VSOP-2 with a high angular resolution.
  • Second Order Gravitational Effects on CMB Temperature Anisotropy in Lambda dominated flat universes, Kenji Tomita, Kaiki Taro Inoue, Phys.Rev.D77:103522,2008, Phys.Rev.D77:103522,2008, Dec. 09 2007
    Summary:We study second order gravitational effects of local inhomogeneities on the
    cosmic microwave background radiation in flat universes with matter and a
    cosmological constant $\Lambda$. We find that the general relativistic
    correction to the Newtonian approximation is negligible at second order
    provided that the size of the inhomogeneous region is sufficiently smaller than
    the horizon scale. For a spherically symmetric top-hat type quasi-linear
    perturbation, the first order temperature fluctuation corresponding to the
    linear integrated Sachs-Wolfe (ISW) effect is enhanced(suppressed) by the
    second order one for a compensated void(lump). As a function of redshift of the
    local inhomogeneity, the second order temperature fluctuations due to evolution
    of the gravitational potential have a peak before the matter-$\Lambda$ equality
    epoch for a fixed comoving size and a density contrast. The second order
    gravitational effects from local quasi-linear inhomogeneities at a redshift z~1
    may significantly affect the cosmic microwave background.
  • Probing the Origin of the Large-angle CMB Anomalies, Kaiki Taro Inoue, Science and Technology No.19 p 11-14 RIST, Kinki University (2007), Science and Technology No.19 p 11-14 RIST, Kinki University (2007), Oct. 12 2007
    Summary:It has been argued that the large-angle cosmic microwave background
    anisotropy has anomalies at 3-sigma level. We review various proposed ideas to
    explain the origin of the anomalies and discuss how we can constrain the
    proposed models using future observational data.
  • Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant, Kaiki Taro Inoue, Joseph Silk, Astrophys.J.664:650-659,2007, Astrophys.J.664:650-659,2007, Dec. 14 2006
    Summary:We explore the large angular scale temperature anisotropies in the cosmic
    microwave background (CMB) due to homogeneous local dust-filled voids in a flat
    Friedmann-Robertson-Walker universe with a cosmological constant. In comparison
    with the equivalent dust-filled void model in the Einstein-de Sitter
    background, we find that the anisotropy for compensated asymptotically
    expanding local voids can be larger because second-order effects enhance the
    linear integrated Sachs-Wolfe (ISW) effect. However, for local voids that
    expand sufficiently faster than the asymptotic velocity of the wall, the
    second-order effect can suppress the fluctuation due to the linear ISW effect.
    A pair of quasi-linear compensated asymptotic local voids with radius
    (2-3)*10^2 ~h^{-1} Mpc and a matter density contrast ~-0.3 can be observed as
    cold spots with a temperature anisotropy Delta T/T~O(10^{-5}) that might help
    explain the observed large-angle CMB anomalies. We predict that the associated
    anisotropy in the local Hubble constant in the direction of the voids could be
    as large as a few percent.
  • Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing, Junji Hisano, Kaiki Taro Inoue, Tomo Takahashi, Phys.Lett.B643:141-146,2006, Phys.Lett.B643:141-146,2006, Aug. 11 2006
    Summary:We propose to observe QSO-galaxy strong lens systems to give a new constraint
    on the damping scale of the initial fluctuations. We find that the future
    observation of submilliarc scale astrometric shifts of the multiple lensed
    images of QSOs would find \sim 10^{(3-9)} M_{\odot} subhalos inside the
    macrolens halo. The superweakly interacting massive particles (superWIMPs)
    produced from a WIMP decay and the warm dark matter (WDM) particles that
    predict a comoving damping scale larger than \sim 2 kpc can be constrained if
    \sim 10^3 M_{\odot} subhalos are detected.
  • Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I, Kaiki Taro Inoue, Joseph Silk, Astrophys.J.648:23-30,2006, Astrophys.J.648:23-30,2006, Feb. 22 2006
    Summary:We explore the large angular scale temperature anisotropies in the cosmic
    microwave background due to expanding homogeneous local voids at redshift z~1.
    A compensated spherically symmetric homogeneous dust-filled void with radius
    \~3*10^2 h^{-1}Mpc, and density contrast ~-0.3 can be observed as a cold spot
    with a temperature anisotropy -1*10^{-5} surrounded by a slightly hotter ring.
    We find that a pair of these circular cold spots separated by ~50 degree can
    account both for the planarity of the octopole and for the alignment between
    the quadrupole and the octopole in the cosmic microwave background (CMB)
    anisotropy. The cold spot in the Galactic southern hemisphere which is
    anomalous at the ~3sigma level can be explained by such a large void at z~1.
    The observed north-south asymmetry in the large-angle CMB power can be
    attributed to the asymmetric distribution of these local voids between the two
    hemispheres. The statistical significance of the low quadrupole is further
    reduced in this interpretation of the large angular scale CMB anomalies.
  • Direct Detection of Intermediate Mass Compact Objects via Submillilensing, Kaiki Taro Inoue, Masashi Chiba, Annual reports by Research Institute for Science and Technology, (2006) 18, p.11-14, Annual reports by Research Institute for Science and Technology, (2006) 18, p.11-14, Dec. 30 2005
    Summary:A galaxy-sized halo may contain a large number of intermediate mass (10^{2-4}
    solar mass) compact objects (IMCOs), which can be intermediate mass black holes
    (IMBHs) or the CDM subhalos. We propose to directly detect the IMBHs by
    observing multiply imaged QSO-galaxy lens systems with a high angular
    resolution (~ 0.03mas), which would be achieved by the next-VLBI space
    missions. The silhouette of the IMBHs would appear as an either monopole-like
    or dipole-like variation at the scale of the Einstein radius against the QSO
    jets. As a byproduct, we can also directly detect the 10^{4-5} solar mass CDM
    subhalos. From a measurement of the local distortion in the surface brightness
    of the QSO jet, we can make a distinction between a point mass (corresponding
    to an IMBH) and an extended structure (corresponding to a CDM subhalo). It
    would be a unique probe of the IMCOs whose nature has been under the veil of
    mistery.
  • Subaru Mid-infrared Imaging of the Quadruple Lenses PG1115+080 and B1422+231: Limits on Substructure Lensing, Masashi Chiba, Takeo Minezaki, Nobunari Kashikawa, Hirokazu Kataza, Kaiki Taro Inoue, Astrophys.J. 627 (2005) 53-61, Astrophys.J. 627 (2005) 53-61, Mar. 23 2005
    Summary:We present mid-infrared imaging at 11.7 mu m for the quadruple lens systems,
    PG1115+080 and B1422+231, using the cooled mid-infrared camera and spectrometer
    (COMICS) attached on the Subaru telescope. These lensed QSOs are characterized
    by their anomalous optical and radio flux ratios as obtained for (A1, A2)
    images of PG1115+080 and (A, B, C) images of B1422+231, respectively, i.e.,
    such flux ratios are hardly reproduced by lens models with smooth mass
    distribution. Our mid-infrared observations for these images have revealed that
    the mid-infrared flux ratio A2/A1 of PG1115+080 is virtually consistent with
    smooth lens models (but inconsistent with the optical flux ratio), whereas for
    B1422+231, the mid-infrared flux ratios among (A, B, C) are in good agreement
    with the radio flux ratios. We also identify a clear infrared bump in the
    spectral energy distributions of these QSOs, thereby indicating that the
    observed mid-infrared fluxes originate from a hot dust torus around a QSO
    nucleus. Based on the size estimate of the dust torus, we place limits on the
    mass of a substructure in these lens systems, causing the anomalous optical or
    radio flux ratios. For PG1115+080, the mass of a substructure inside an
    Einstein radius, M_E, is < 16 Msun, corresponding to either a star or a
    low-mass CDM subhalo having the mass of M_{100}^{SIS} < 2.2 * 10^4 Msun inside
    radius of 100 pc if modeled as a singular isothermal sphere (SIS). For
    B1422+231, we obtain M_E > 209 Msun, indicating that a CDM subhalo is more
    likely, having the mass of M_{100}^{SIS} > 7.4 * 10^4 Msun
  • Three-dimensional Mapping of CDM Substructure at Submillimeter Wavelengths, Kaiki Taro Inoue, Masashi Chiba, Astrophys.J.633:23-28,2005, Astrophys.J.633:23-28,2005, Mar. 09 2005
    Summary:The cold dark matter (CDM) structure formation model predicts that about 5-10
    percent of a typical galactic halo of mass $\sim 10^{12} \ms$ is in
    substructures with masses $\lesssim 10^8 \ms$. To directly detect such
    substructures, we propose to observe dust continuum emission from a strongly
    lensed QSO-host galaxy using a large submillimeter interferometer array with a
    high angular resolution of $\sim 0.01$arcsec such as the planned Atacama Large
    Submillimeter Array (ALMA). To assess their observational feasibility, we
    numerically simulate millilensing of an extended circular source by a CDM
    substructure modeled as a tidally truncated singular isothermal sphere (SIS)
    embedded in a typical QSO-galaxy lens system, B1422+231, modeled as a singular
    isothermal ellipsoid (SIE) with an external constant shear and a constant
    convergence. Assuming an angular resolution of 0.01arcsec, we find that the
    angular positions of $\sim 10^8 \ms$ substructures at several kpc from the
    center of the macrolens halo can be directly measured if the size of the dust
    continuum emission region and the gradient of the surface brightness at the
    position of the perturber are sufficiently large. From the astrometric shift on
    a scale of a few times $10~$mas of an image perturbed by a subhalo with respect
    to an unperturbed macrolensed image, we can break the degeneracy between
    subhalo mass and distance provided that macrolensing parameters are determined
    from positions and fluxes of multiple images.
  • Extended Source Effects in Substructure Lensing, Kaiki Taro Inoue, Masashi Chiba, Astrophys.J. 634 (2005) 77-89, Astrophys.J. 634 (2005) 77-89, Nov. 07 2004
    Summary:We investigate the extended source size effects on gravitational lensing in
    which a lens consists of a smooth potential and small mass clumps
    (``substructure lensing''). We first consider a lens model that consists of a
    clump modeled as a singular isothermal sphere (SIS) and a primary lens modeled
    as an external background shear and convergence. For this simple model, we
    derive analytic formulae for (de)magnification of circularly symmetric top-hat
    sources with three types of parity for their lensed images, namely, positive,
    negative, and doubly negative parities. Provided that the source size is
    sufficiently larger than the Einstein radius of the SIS, we find that in the
    positive (doubly negative) parity case, an extended source is always magnified
    (demagnified) in comparison with the unperturbed macrolens system, whereas in
    the negative parity case, the (de)magnification effect, which depends on the
    sign of convergence minus unity is weaker than those in other parities. It is
    shown that a measurement of the distortion pattern in a multiply lensed image
    enables us to break the degeneracy between the lensing effects of clump mass
    and those of clump distance if lensing parameters of the relevant macrolens
    model are determined from the position and flux of multiple images. We also
    show that an actual density profile of a clump can be directly measured by
    analyzing the ``fine structure'' in a multiply lensed image within the Einstein
    radius of the clump.
  • Direct Mapping of Massive Compact Objects in Extragalactic Dark Halos, Kaiki Taro Inoue, Masashi Chiba, Astrophys.J. 591 (2003) L83, Astrophys.J. 591 (2003) L83, Apr. 26 2003
    Summary:A significant fraction of non-baryonic or baryonic dark matter in galactic
    halos may consist of MASsive Compact Objects (MASCOs) with mass
    M=10^{1-4}M_{sun}. Possible candidates for such compact objects include
    primordial black holes or remnants of primordial (Population III) stars. We
    propose a method for directly detecting MASCOs in extragalactic halos, using
    the VLBI techniques with extremely high resolution. If a galactic halo
    comprising a large number of MASCOs produces multiple images of a background
    radio-loud QSO by gravitational lensing, then a high-resolution radio map of
    each macro-lensed image should reveal microlensing effects by MASCOs. To assess
    their observational feasibility, we simulate microlensing of the radio-loud,
    four-image lensed QSO, B1422+231, assuming angular resolution of ~0.01 mas.
    MASCOs are represented by point masses. For comparison, we also simulate
    microlensing of B1422+231 by singular isothermal spheres. We find that the
    surface brightness of the macro-lensed images shows distinct spatial patterns
    on the scale of the Einstein radius of the perturbers. In the case of
    point-mass perturbers, many tiny dark spots also appear in the macro-lensed
    images associated with a decrease in the surface brightness toward the fringe
    of the original QSO image, whereas no such spots are available in the SIS
    models. Based on the size, position and magnified or demagnified patterns of
    images, we shall be able to determine the mass and density profile of a MASCO
    as well as its spatial distribution and abundance in a galactic halo.
  • Gravitational Waves from Sub-lunar Mass Primordial Black Hole Binaries - A New Probe of Extradimensions, Kaiki Taro Inoue, Takahiro Tanaka, Phys.Rev.Lett. 91 (2003) 021101, Phys.Rev.Lett. 91 (2003) 021101, Mar. 16 2003
    Summary:In many braneworld models, gravity is largely modified at the electro-weak
    scale ~ 1TeV. In such models, primordial black holes (PBHs) with lunar mass M ~
    10^{-7}M_sun might have been produced when the temperature of the universe was
    at ~ 1TeV. If a significant fraction of the dark halo of our galaxy consists of
    these lunar mass PBHs, a huge number of BH binaries will exist in our
    neighborhood. Third generation detectors such as EURO can detect gravitational
    waves from these binaries, and can also determine their chirp mass. With a new
    detector designed to be sensitive at high frequency bands greater than 1 kHz,
    the existence of extradimensions could be confirmed.
  • How large is our universe?, Kaiki Taro Inoue, Naoshi Sugiyama, Phys.Rev. D67 (2003) 043003, Phys.Rev. D67 (2003) 043003, May 23 2002
    Summary:We reexamine constraints on the spatial size of closed toroidal models with
    cold dark matter and the cosmological constant from cosmic microwave
    background. We carry out Bayesian analyses using the Cosmic Background Explorer
    (COBE) data properly taking into account the statistically anisotropic
    correlation, i.e., off-diagonal elements in the covariance. We find that the
    COBE constraint becomes more stringent in comparison with that using only the
    angular power spectrum, if the likelihood is marginalized over the orientation
    of the observer. For some limited choices of orientations, the fit to the COBE
    data is considerably better than that of the infinite counterpart. The best-fit
    matter normalization is increased because of large-angle suppression in the
    power and the global anisotropy of the temperature fluctuations. We also study
    several deformed closed toroidal models in which the fundamental cell is
    described by a rectangular box. In contrast to the cubic models, the
    large-angle power can be enhanced in comparison with the infinite counterparts
    if the cell is sufficiently squashed in a certain direction. It turns out that
    constraints on some slightly deformed models are less stringent. We comment on
    how these results affect our understanding of the global topology of our
    universe.
  • Analytic Approach to the Cloud-in-cloud Problem for Non-Gaussian Density Fluctuations, Kaiki Taro Inoue, Masahiro Nagashima, Astrophys.J. 574 (2002) 9-18, Astrophys.J. 574 (2002) 9-18, Oct. 23 2001
    Summary:We revisit the cloud-in-cloud problem for non-Gaussian density fluctuations.
    We show that the extended Press-Schechter (EPS) formalism for non-Gaussian
    fluctuations has a flaw in describing mass functions regardless of type of
    filtering. As an example, we consider non-Gaussian models in which density
    fluctuations at a point obeys a \chi^2 distribution with \nu degrees of
    freedom. We find that mass functions predicted by using an integral formula
    proposed by Jedamzik, and Yano, Nagashima and Gouda, properly taking into
    account correlation between objects at different scales, deviate from those
    predicted by using the EPS formalism, especially for strongly non-Gaussian
    fluctuations. Our results for the mass function at large mass scales are
    consistent with those by Avelino and Viana obtained from numerical simulations.
  • Exploring Topology of the Universe in the Cosmic Microwave Background, Kaiki Taro Inoue, Mar. 11 2001
    Summary:We study the effect of global topology of the spatial geometry on the cosmic
    microwave background (CMB) for closed flat and closed hyperbolic models in
    which the spatial hypersurface is multiply connected. If the CMB temperature
    fluctuations were entirely produced at the last scattering, then the
    large-angle fluctuations would be much suppressed in comparison with the simply
    connected counterparts which is at variance with the observational data.
    However, as we shall show in this thesis, for low matter density models the
    observational constraints are less stringent since a large amount of
    large-angle fluctuations could be produced at late times. On the other hand, a
    slight suppression in large-angle temperature correlations in such models
    explains rather naturally the observed anomalously low quadrupole which is
    incompatible with the prediction of the "standard"
    Friedmann-Robertson-Walker-Lemaitre models. Interestingly, moreover, the
    development in the astronomical observation technology has made it possible to
    directly explore the imprint of the non-trivial topology by looking for
    identical objects so called "ghosts" in wide separated directions. For the CMB
    temperature fluctuations identical patterns would appear on a pair of circles
    in the sky. Another interesting feature is the non-Gaussianity in the
    temperature fluctuations. Inhomogeneous and anisotropic Gaussian fluctuations
    for a particular choice of position and orientation are regarded as
    non-Gaussian fluctuations for a homogeneous and isotropic ensemble.
  • Are Compact Hyperbolic Models Observationally Ruled Out?, Kaiki Taro Inoue, Prog.Theor.Phys. 106 (2001) 39, Prog.Theor.Phys. 106 (2001) 39, Feb. 13 2001
    Summary:We revisit the observational constraints on compact(closed) hyperbolic(CH)
    models from cosmic microwave background(CMB). We carry out Bayesian analyses
    for CH models with volume comparable to the cube of the present curvature
    radius using the COBE-DMR data and show that a slight suppression in the
    large-angle temperature correlations owing to the non-trivial topology explains
    rather naturally the observed anomalously low quadrupole which is incompatible
    with the prediction of the standard infinite Friedmann-Robertson-Walker models.
    While most of positions and orientations are ruled out, the likelihoods of CH
    models are found to be much better than those of infinite counterparts for some
    specific positions and orientations of the observer, leading to less stringent
    constraints on the volume of the manifolds. Even if the spatial geometry is
    nearly flat as $\Omega_{tot}=0.9-0.95$, suppression of the angular power on
    large angular scales is still prominent for CH models with volume much less
    than the cube of the present curvature radius if the cosmological constant is
    dominant at present.
  • Cosmic Microwave Background in Closed Multiply Connected Universes, Kaiki Taro Inoue, Nov. 29 2000
    Summary:We have investigated the cosmic microwave background (CMB) anisotropy in
    closed multiply connected universes
    (flat and hyperbolic) with low matter density. We show that the COBE
    constraints on these low matter density models with non-trivial topology are
    less stringent since a large amount of CMB anisotropy on large angular scales
    can be produced due to the decay of the gravitational potential at late time.
  • COBE Constraints on a Compact Toroidal Low-density Universe, Kaiki Taro Inoue, Class.Quant.Grav. 18 (2001) 1967-1977, Class.Quant.Grav. 18 (2001) 1967-1977, Nov. 25 2000
    Summary:In this paper, the cosmic microwave background (CMB) anisotropy in a
    multiply-connected compact flat 3-torus model with the cosmological constant is
    investigated. Using the COBE-DMR 4-year data, a full Bayesian analysis revealed
    that the constraint on the topology of the flat 3-torus model with
    low-matter-density is less stringent. As in compact hyperbolic models, the
    large-angle temperature fluctuations can be produced as the gravitational
    potential decays at the $\Lambda$-dominant epoch well after the last
    scattering. The maximum allowed number $N$ of images of the cell (fundamental
    domain) within the observable region at present is approximately 49 for
    $\Omega_m=0.1$ and $\Omega_\Lambda=0.9$ whereas $N\sim8$ for $\Omega_m=1.0$ and
    $\Omega_\Lambda=0$.
  • Numerical Study of Length Spectra and Low-lying Eigenvalue Spectra of Compact Hyperbolic 3-manifolds, Kaiki Taro Inoue, Class.Quant.Grav. 18 No.4 629-652 (2001), Class.Quant.Grav. 18 No.4 629-652 (2001), Nov. 09 2000
    Summary:In this paper, we numerically investigate the length spectra and the
    low-lying eigenvalue spectra of the Laplace-Beltrami operator for a large
    number of small compact(closed) hyperbolic (CH) 3-manifolds. The first non-zero
    eigenvalues have been successfully computed using the periodic orbit sum
    method, which are compared with various geometric quantities such as volume,
    diameter and length of the shortest periodic geodesic of the manifolds. The
    deviation of low-lying eigenvalue spectra of manifolds converging to a cusped
    hyperbolic manifold from the asymptotic distribution has been measured by
    $\zeta-$ function and spectral distance.
  • Geometric Gaussianity and Non-Gaussianity in the Cosmic Microwave Background, Kaiki Taro Inoue, Phys.Rev.D62:103001,2000, Phys.Rev.D62:103001,2000, Feb. 14 2000
    Summary:In this paper, Gaussianity of eigenmodes and non-Gaussianity in the Cosmic
    Microwave Background (CMB) temperature fluctuations in two smallest compact
    hyperbolic (CH) models are investigated. First, it is numerically found that
    the expansion coefficients of low-lying eigenmodes on the two CH manifolds
    behave as if they are Gaussian random numbers at almost all the places. Next,
    non-Gaussianity of the temperature fluctuations in the (l,m) space in these
    models is studied. Assuming that the initial fluctuations are Gaussian, the
    real expansion coefficients b_{l m} of the temperature fluctuations in the sky
    are found to be distinctively non-Gaussian. In particular, the cosmic variances
    are found to be much larger than that for Gaussian models. On the other hand,
    the anisotropic structure is vastly erased if one averages the fluctuations at
    a number of different observing points because of the Gaussian
    pseudo-randomness of the eigenmodes. Thus the dominant contribution to the
    two-point correlation functions comes from the isotropic terms described by the
    angular power spectra C_l. Finally, topological quantities: the total length
    and the genus of isotemperature contours are investigated. The variances of
    total length and genus at high and low threshold levels are found to be
    considerably larger than that of Gaussian models while the means almost agree
    with them.
  • Temperature correlations in a compact hyperbolic universe, Kaiki Taro Inoue, Kenji Tomita, Naoshi Sugiyama, Mon.Not.Roy.Astron.Soc. 314 (2000) L21, Mon.Not.Roy.Astron.Soc. 314 (2000) L21, Jun. 18 1999
    Summary:The effect of a non-trivial topology on the temperature correlations on the
    cosmic microwave background (CMB) in a small compact hyperbolic universe with
    volume comparable to the cube of the curvature radius is investigated. Because
    the bulk of large-angular CMB fluctuations is produced at the late epoch in low
    $\Omega_0$ models, the effect of a long wavelength cut-off due to the periodic
    structure does not lead to the significant suppression of large-angular power
    as in compact flat models. The angular power spectra are consistent with the
    COBE data for $\Omega_0 \ge 0.1$.
  • CMB Anisotropy in Compact Hyperbolic Universes, Kaiki Taro Inoue, Mar. 30 1999
    Summary:Measurements of CMB anisotropy are ideal experiments for discovering the
    non-trivial global topology of the universe. To evaluate the CMB anisotropy in
    multiply-connected compact cosmological models, one needs to compute eigenmodes
    of the Laplace-Beltrami operator. We numerically obtain the eigenmodes on a
    compact 3-hyperbolic space cataloged as $m003(-2,3)$ in SnapPea (computer
    program by Jeff Weeks) using the direct boundary element method, which enables
    one to simulate the CMB in multiply-connected compact models with high
    precision. The angular power spectra $C_{l}$'s ($2 \leq l\leq18$) are
    calculated using computed eigenmodes for $5.4\leqk<10$ and Gaussian random
    approximation for the expansion coefficients for $10\leqk<20$. Assuming that
    the initial power spectrum is the Harrison-Zeldovich spectrum, the computed
    $C_l$'s are consistent with the COBE data for $0.1 \leq\Omega_o \leq 0.6$.
    In low $\Omega_o$ models, the large-angular fluctuations can be produced at
    periods after the last scattering as the curvature perturbations decay in the
    curvature dominant era.
  • Computation of eigenmodes on a compact hyperbolic 3-space, Kaiki Taro Inoue, Class.Quant.Grav. 16 (1999) 3071-3094, Class.Quant.Grav. 16 (1999) 3071-3094, Oct. 02 1998
    Summary:Measurements of cosmic microwave background (CMB) anisotropy are ideal
    experiments for discovering the non-trivial global topology of the universe. To
    evaluate the CMB anisotropy in multiply-connected compact cosmological models,
    one needs to compute the eigenmodes of the Laplace-Beltrami operator. Using the
    direct boundary element method, we numerically obtain the low-lying eigenmodes
    on a compact hyperbolic 3-space called the Thurston manifold which is the
    second smallest in the known compact hyperbolic 3-manifolds. The computed
    eigenmodes are expanded in terms of eigenmodes on the unit three-dimensional
    pseudosphere. We numerically find that the expansion coefficients behave as
    Gaussian pseudo-random numbers for low-lying eigenmodes. The observed
    gaussianity in the CMB fluctuations can partially be attributed to the Gaussian
    pseudo-randomness of the expansion coefficients assuming that the Gaussian
    pseudo-randomness is the universal property of the compact hyperbolic spaces.

Conference Activities & Talks

  • 巨大低密度領域におけるハローの質量関数とピーク統計, 樋口祐一, 井上開輝, 日本天文学会年会講演予稿集,   2018 08 20
  • クェーサーMG0751+2716の重力レンズモデル, 堀口康男, 井上開輝, 日本天文学会年会講演予稿集,   2018 02 20
  • トラフレンズによる10kpc以下の密度ゆらぎの制限, 井上開輝, 石山智明, 浜名崇, 日本天文学会年会講演予稿集,   2018 02 20
  • 拡がった光源に対する重力レンズ効果のモデリング, 茂野智幸, 井上開輝, 日本天文学会年会講演予稿集,   2017 08 20
  • 弱重力レンズ効果によるCMB Cold Spot方向の質量分布測定, 樋口祐一, 井上開輝, 日本天文学会年会講演予稿集,   2017 08 20
  • 4重像レンズQSOにおける暗黒矮小銀河のエビデンス, 井上開輝, 松下聡樹, 峰崎岳夫, 千葉柾司, 日本天文学会年会講演予稿集,   2017 02 28
  • 弱重力レンズ効果による超ボイドの重力的撮像, 井上開輝, 西澤淳, 浜名崇, 樋口祐一, 宮武広直, 日本天文学会年会講演予稿集,   2016 08 20
  • 4重像レンズにおけるフラックス比異常の起源について, 井上開輝, 日本天文学会年会講演予稿集,   2016 02 20
  • On the Origin of Flux Ratio Anomaly in Quadruple Lens Systems, Kaiki Taro Inoue, MNRAS (2016) 461 (1), p164-175,   2016 01 18
    Summary:We explore the origin of flux ratio anomaly in quadruple lens systems. Using a semi-analytic method based on $N$-body simulations, we estimate the effect of possible magnification perturbation caused by subhaloes with a mass scale of <$\sim 10^9\,h^{-1} \textrm{M}_\odot$ in lensing galaxy haloes. Taking into account astrometric shifts, assuming that the primary lens is described by a singular isothermal ellipsoid, the expected change to the flux ratios per a multiply lensed image is just a few percent and the mean of the expected convergence perturbation at the effective Einstein radius of the lensing galaxy halo is $ 0.003$, corresponding to the mean of the ratio of a projected dark matter mass fraction in subhaloes at the effective Einstein radius $0.006$. In contrast, the expected change to the flux ratio caused by line-of-sight structures is typically $\sim 10$ percent and the mean of the convergence perturbation is $0.008$, corresponding to $0.017$. The contribution of magnification perturbation caused by subhaloes is $\sim 40$ percent of the total at a source redshift $z_S= 0.7$ and decreases monotonically in $z_S$ to $\sim 20$ percent at $z_S= 3.6$. Assuming statistical isotropy, the convergence perturbation estimated from observed 11 quadruple lens systems has a positive correlation with the source redshift $z_S$, which is much stronger than that with the lens redshift $z_L$. This feature also supports an idea that the flux ratio anomaly is caused mainly by line-of-sight structures rather than subhaloes. We also discuss about a possible imprint of line-of-sight structures in demagnification of minimum images due to locally underdense structures in the line of sight.
  • サブミリレンズ銀河SDP.81におけるダークマター小構造の痕跡, 井上開輝, 峰崎岳夫, 松下聡樹, 千葉柾司, 日本天文学会年会講演予稿集,   2015 08 20
  • 4重像重力レンズを用いた温かいダークマターの質量の制限, 井上開輝, 高橋龍一, 高橋智, 石山智明, 日本天文学会年会講演予稿集,   2015 02 20
  • スペース重力波アンテナDECIGO計画(55):DECIGO/DPFの概要, 安東正樹, 川村静児, 瀬戸直樹, 中村卓史, 坪野公夫, 佐藤修一, 田中貴浩, 船木一幸, 沼田健司, 神田展行, 井岡邦仁, 高島健, 横山順一, 阿久津智忠, 武者満, 上田暁俊, 麻生洋一, 新谷昌人, 坂井真一郎, 青柳巧介, 我妻一博, 浅田秀樹, 新井宏二, 池上健, 石川毅彦, 石崎秀晴, 石原秀樹, 和泉究, 市來淨與, 伊東宏之, 伊藤洋介, 井上開輝, 植田憲一, 牛場崇文, 歌島昌由, 江口智士, 江尻悠美子, 榎基宏, 戎崎俊一, 江里口良治, 日本物理学会講演概要集,   2014 08 22
  • ”Probing the origin of flux-ratio anomalies in quadruple lenses with ALMA”, Kaiki Taro Inoue,   2014 03 24
  • Probing the origin of flux-ratio anomalies in quadruple lenses with ALMA, INOUE Kaiki, MATSUSHITA Satoki, CHIBA Masashi, MINEZAKI Takeo, TAKAHASHI Ryuichi, 日本天文学会年会講演予稿集,   2014 02 20
  • "Gravitational mapping of IMBH in the extragalactic halos", Kaiki Taro Inoue,   2013 11 11
  • "Probing the origin of dark matter with mini-gravitational lensing", Kaiki Taro Inoue,   2013 06 27 , 招待有り
  • ”Weak Lensing by Line-of-sight Halos as the Origin of Flux-ratio Anomalies in Quadruply Lensed QSOs”, Kaiki Taro Inoue,   2013 03 23

Misc

  • Discovery of an unusually compact lensed Lyman Break Galaxy from Hyper Suprime-Cam Survey, Anton T. Jaelani, Anupreeta More, Alessandro Sonnenfeld, Masamune Oguri, Cristian E. Rusu, Kenneth C. Wong, James H, H. Chan, Sherry H. Suyu, Issha Kayo, Chien-Hsiu Lee, Kaiki T. Inoue,   2019 08 31 , http://arxiv.org/abs/1909.00120v1
    Summary:We report a serendipitous discovery of HSC J0904--0102, a quadruply lensed
    Lyman Break Galaxy (LBG) in the Survey of Gravitationally Lensed Objects in
    Hyper Suprime-Cam Imaging (SuGOHI). Owing to its point-like appearance, the
    source was thought to be a lensed active galactic nucleus. As a result, we
    obtained follow-up spectroscopic data with the Gemini Multi-Object
    Spectrographs on Gemini South Telescope which confirmed this to be a lens
    system. The deflecting foreground galaxy is a typical early-type galaxy but at
    a high redshift of $z_{\ell} = 0.957$ with stellar velocity dispersion
    $\sigma_v=259\pm56$ km~s$^{-1}$ and the lensed source turned out to be an LBG
    at $z_{\rm s} = 3.403$, based on the sharp drop bluewards of Ly$\alpha$ and
    other absorption features. A simple lens mass model for the system assuming a
    Singular Isothermal Ellipsoid yields an Einstein radius of $\theta_{\rm Ein} =
    1. 23$", a total mass within the Einstein radius for the deflector of $M_{\rm
    Ein} = (5.55\pm 0.31) \times 10^{11}M_{\odot}$ corresponding to the velocity
    dispersion of the deflector of $\sigma_{\rm SIE}= 283\pm4$ km~s$^{-1}$, which
    is in good agreement with the value derived spectroscopically, and a
    magnification factor for more isolated lensed LBG image of $\sim 6.5$. After
    comparing with other lensed LBGs and typical $z\sim4$ LBG populations, our LBG
    is unusually compact, an outlier of over 2$\sigma$. Together with a previously
    discovered SuGOHI lens (More et al. 2017) that had similarly highly compact
    nature, we believe that the HSC Survey is extending LBG studies down to smaller
    sizes.
  • Dark Matter Substructure in Lensing Galaxies, Masashi Chiba, Takeo Minezaki, Kaiki T. Inoue, Nobunari Kashikawa, Hirokazu Kataza, Hajime Sugai,   2008 04 02 , http://arxiv.org/abs/0804.0282v1
    Summary:To set useful limits on the abundance of small-scale dark matter halos
    (subhalos) in a galaxy scale, we have carried out mid-infrared imaging and
    integral-field spectroscopy for a sample of quadruple lens systems showing
    anomalous flux ratios. These observations using Subaru have been successful for
    distinguishing millilensing by subhalos from microlensing by stars. Current
    status for our lensing analysis of dark matter substructure is reported.
  • Gravitational Radiation from Coalescing Supermassive Black Hole Binaries in a Hierarchical Galaxy Formation Model, Motohiro Enoki, Kaiki T. Inoue, Masahiro Nagashima, Naoshi Sugiyama,   2005 02 25 , http://arxiv.org/abs/astro-ph/0502529v2
    Summary:We investigate the expected gravitational wave emission from coalescing
    supermassive black hole (SMBH) binaries resulting from mergers of their host
    galaxies. We employ a semi-analytic model of galaxy and quasar formation based
    on the hierarchical clustering scenario to estimate the amplitude of the
    expected stochastic gravitational wave background owing to inspiraling SMBH
    binaries and bursts rates owing to the SMBH binary coalescence events. We find
    that the characteristic strain amplitude of the background radiation is $h_c(f)
    \sim 10^{-16} (f/1 \mu {\rm Hz})^{-2/3}$ for $f \lesssim 1 \mu {\rm Hz}$. The
    main contribution to the total strain amplitude of the background radiation
    comes from SMBH coalescence events at $0<z<1$. We also find that a future
    space-based gravitational wave interferometer such as the planned \textit{Laser
    Interferometer Space Antenna} ({\sl LISA}) might detect intense gravitational
    wave bursts associated with coalescence of SMBH binaries with total mass
    $M_{\rm tot} < 10^7 M_{\odot}$ at $z \gtrsim 2$ at a rate $ \sim 1.0 {\rm
    yr}^{-1}$. Our model predicts that burst signals with a larger amplitude
    $h_{\rm burst} \sim 10^{-15}$ correspond to coalescence events of massive SMBH
    binary with total mass $M_{\rm tot} \sim 10^8 M_{\odot}$ at low redshift $ z
    \lesssim 1$ at a rate $ \sim 0.1 {\rm yr}^{-1}$ whereas those with a smaller
    amplitude $h_{\rm burst} \sim 10^{-17}$ correspond to coalescence events of
    less massive SMBH binary with total mass $M_{\rm tot} \sim 10^6 M_{\odot}$ at
    high redshift $ z \gtrsim 3$.
  • Gravitational Waves from Supermassive Black Hole Coalescence in a Hierarchical Galaxy Formation Model, Motohiro Enoki, Kaiki T. Inoue, Masahiro Nagashima, Naoshi Sugiyama, Astrophys.J. 615 (2004) 19,   2004 04 21 , 10.1086/424475, http://arxiv.org/abs/astro-ph/0404389v2
    Summary:We investigate the expected gravitational wave emission from coalescing
    supermassive black hole (SMBH) binaries resulting from mergers of their host
    galaxies. When galaxies merge, the SMBHs in the host galaxies sink to the
    center of the new merged galaxy and form a binary system. We employ a
    semi-analytic model of galaxy and quasar formation based on the hierarchical
    clustering scenario to estimate the amplitude of the expected stochastic
    gravitational wave background owing to inspiraling SMBH binaries and bursts
    owing to the SMBH binary coalescence events. We find that the characteristic
    strain amplitude of the background radiation is $h_c(f) \sim 10^{-16} (f/1 \mu
    {\rm Hz})^{-2/3}$ for $f \lesssim 1 \mu {\rm Hz}$ just below the detection
    limit from measurements of the pulsar timing provided that SMBHs coalesce
    simultaneously when host galaxies merge. The main contribution to the total
    strain amplitude of the background radiation comes from SMBH coalescence events
    at $0<z<1$. We also find that a future space-based gravitational wave
    interferometer such as the planned \textit{Laser Interferometer Space Antenna}
    ({\sl LISA}) might detect intense gravitational wave bursts associated with
    coalescence of SMBH binaries with total mass $M_{\rm tot} < 10^7 M_{\odot}$ at
    $z \gtrsim 2$ at a rate $ \sim 1.0 {\rm yr}^{-1}$. Our model predicts that
    burst signals with a larger amplitude $h_{\rm burst} \sim 10^{-15}$ correspond
    to coalescence events of massive SMBH binary with total mass $M_{\rm tot} \sim
    10^8 M_{\odot}$ at low redshift $ z \lesssim 1$ at a rate $ \sim 0.1 {\rm
    yr}^{-1}$ whereas those with a smaller amplitude $h_{\rm burst} \sim 10^{-17}$
    correspond to coalescence events of less massive SMBH binary with total mass
    $M_{\rm tot} \sim 10^6 M_{\odot}$ at high redshift $ z \gtrsim 3$.

Research Grants & Projects

  • Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(Kiban-B), Probing the origin of primordial minihaloes with gravitational lensing
  • Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(Wakate(B)), Probing theory of gravity via inhomogeneity of the universe, We find that the evolution of gravitational potential of super-structures in accelerating universes plays an important role as a cause of claimed anomalies in the large-angle cosmic microwave background temperature anisotropy. In particular, the effects of low density regions with a radius of 200-300h/Mpc are most important and their abundance is at odd with the expected value in theΛCDM model at more than 3σlevel.
  • Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(Wakate(B)), Probing the global and local inhomogeneities of the universe with CMB, 非線形重力ポテンシャルの進化による温度ゆらぎ生成機構の解明「薄い殻」近似、摂動論、Lemaitre-Tolman-Bondi時空モデルの3つの計算方法を駆使して明らかになったのは以下の四点である。(1)宇宙項入りの平坦Friedmann-Robertoson-Walker(FRW)モデルでは、Einsten-de Sitter宇宙の場合と異なり、温度ゆらぎに対して、密度コントラストの一次の項も寄与する。又、密度コントラストの一次の項と二次の項はボイドの場合相関する。(2)二次の項はポテンシャルの符号によらず、常に温度を下げる働きがある。従って、低赤方偏移では、ボイド領域を通過した宇宙背景輻射光子は、より低温になり、質量集中の領域を通過した光子は高温になる。しかし、二次の効果がより効くとやや温度が下がる。又、高赤方偏移の質量集中を通過した光子に対しては一次の効果より二次の効果が利くため、温度揺らぎは負になる。(3)標準モデル(宇宙項入りの平坦FRWモデル)の予測する大角度スケールにおける非線形重力ポテンシャル進化による温度揺らぎの平均値のオーダーは大き目に見積もって1億分の1程度であり、その効果は線形積分Sachs-Wolfe効果に比べて無視できる。(4)しかしながら、高赤方偏移の天体のみの寄与を考えると、その線形積分Sachs-Wolfe効果は質量優勢期において消滅するため、一次の効果対する二次の効果は高赤方偏移では無視できなくなる。