■Faculty | Department of Science / Graduate School of Science and Engineering Research |

■Position | Professor |

■Degree | PhD |

■Commentator Guide | https://www.kindai.ac.jp/meikan/272-inoue-kaiki.html |

■URL | |

Last Updated :2020/04/03

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

- 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

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

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

- 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.

- 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

- 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/1909.00120v1Summary: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/0804.0282v1Summary: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/0502529v2Summary: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/0404389v2Summary: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$.

- 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。