Kiyotomo Ichiki
A5084797980- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Black Holes and Theoretical Physics
- Scientific Research and Discoveries
- Particle physics theoretical and experimental studies
- Neutrino Physics Research
- Superconducting and THz Device Technology
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- Relativity and Gravitational Theory
- Advanced Differential Geometry Research
- Geomagnetism and Paleomagnetism Studies
- History and Developments in Astronomy
- Antenna Design and Optimization
- Radio Wave Propagation Studies
- Computational Physics and Python Applications
- Astrophysics and Star Formation Studies
Nagoya University
2015-2024
Obayashi (Japan)
2014-2024
University of Rome Tor Vergata
2024
Centre National de la Recherche Scientifique
2020
McGill University
2020
Yunnan University
2020
Stockholm University
2020
Université Paris-Sud
2020
Cardiff University
2020
University of California, San Diego
2020
We derive the complete spectrum of gravitational waves induced by primordial scalar perturbations ranging over all observable wavelengths. This scalar-induced contribution can be computed directly from observed and general relativity is, in this sense, independent cosmological model for generating perturbations. The is scale invariant on small scales, but has an interesting dependence large intermediate where do not redshift are hence enhanced relative to background density Universe. tensor...
Abstract The Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future Japanese space mission with frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection primordial gravitational waves, which could have been produced during inflationary period right after birth Universe. There are many other scientific objectives DECIGO, including direct measurement acceleration expansion Universe, and reliable accurate predictions timing locations neutron star/black hole binary...
Abstract LiteBIRD, the Lite (Light) satellite for study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission primordial cosmology fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as strategic large-class (L-class) mission, with an expected launch late 2020s using JAXA’s H3 rocket. planned to orbit Sun–Earth Lagrangian point L2, where it will map microwave over entire sky three years, telescopes 15...
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes.Whereas detections have been made sources (Lyman-α emitters, quasars drop-outs) in this redshift regime relatively small fields view, no direct detection neutral hydrogen, via redshifted 21-cm line, has yet established.Such a expected coming years, surveys, could entire universe from z ∼6-200 astrophysical cosmological studies, opening not only Reionization, but also...
The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as clusters galaxies, is yet unclear. If second-order couplings between photons electrons considered, then cosmological density fluctuations, which explain large-scale structure universe, can also produce scales before epoch recombination. By evaluating power spectrum these a range we show here 10(-18.1) gauss generated at 1-megaparsec scale be stronger smaller (10(-14.1) 10 kiloparsecs)....
We study the spherical, top-hat collapse model for a mixed dark matter including cold (CDM) and massive neutrinos of mass scales ranging from m_nu= 0.05 to few 0.1eV, range lower- upper-bounds implied neutrino oscillation experiments cosmological constraints. To develop this model, we properly take into account relative differences between density perturbation amplitudes different components (radiation, baryon, CDM neutrinos) around overdensity region assuming adiabatic initial conditions....
Abstract We show that the cosmic birefringence and miscalibrated polarization angles can be determined simultaneously by microwave background (CMB) experiments using cross-correlation between $E$- $B$-mode data. This is possible because of CMB are rotated both miscalibration effects, whereas those Galactic foreground emission only latter. Our method does not require prior knowledge power spectra emission, but uses spectra. Specifically, we relate observed $EB$ correlation to difference...
We analyze the observational constraints on brane-world cosmology whereby universe is described as a three-brane embedded in five-dimensional anti--de Sitter space. In this brane-universe cosmology, Friedmann equation modified by appearance of extra terms which derive from existence dimensions. present work we concentrate ``dark radiation'' term diminishes with cosmic scale factor ${a}^{\ensuremath{-}4}.$ show that, although primordial abundances allow only small contribution when positive,...
The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies cosmic microwave background (CMB). It also provides plausible explanation for possible disparity between observations theoretical fits to CMB power spectrum. Here we report on calculations not only numerical spectrum from PMF, but correlations PMF primary curvature perturbations. We then deduce precise estimate effect all modes find that affects TT (temperature fluctuation), TE...
We present the newest statistical and numerical analysis of matter cosmic microwave background power spectrum with effects primordial magnetic field (PMF) included. New limits to PMF strength spectral index are obtained based upon accumulated data for both CMB spectra on small angular scales. find that a maximum develops in probability distribution magnitude $|{B}_{\ensuremath{\lambda}}|=0.85\ifmmode\pm\else\textpm\fi{}1.25(\ifmmode\pm\else\textpm\fi{}1\ensuremath{\sigma})\text{ }\text{...
Lower bounds are derived on the amplitude B of intergalactic magnetic fields (IGMFs) in region between Galaxy and blazar Mrk 421, from constraints delayed GeV pair-echo flux that emitted by secondary e^-e^+ produced \gamma\gamma interactions primary TeV gamma-rays cosmic infrared background. The distribution galaxies mapped Sloan Digital Sky Survey shows this is dominated a large void. We utilize data long-term, simultaneous GeV-TeV observations Fermi Large Area Telescope ARGO-YBJ experiment...
Redshifted 21 cm signal is a promising tool to investigate the state of intergalactic medium (IGM) in cosmic dawn (CD) and epoch reionization (EoR). In our previous work, we studied variance skewness fluctuations give clear interpretation power spectrum found that good indicator when X-ray heating becomes effective. Thus, non-Gaussian feature spatial distribution expected be useful astrophysical effects CD EoR. this paper, order such more detail, focus on bispectrum signal. It brightness...
We perform a Fisher analysis to estimate the expected constraints on epoch-of-reionization (EoR) model parameters (i.e. minimum virial temperature, ionizing efficiency and mean free path of photons) taking into account thermal noise existing telescopes, MWA LOFAR. consider how inclusion 21-cm bispectrum improves compared using power spectrum alone. Assuming that we perfectly remove foregrounds, found bispectrum, which is calculated by 21-cmfast code, can constrain EoR more tightly than since...
Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application future satellite CMB polarization experiments. LiteBIRD is most advanced phase among such satellites, targeting its launch Japanese Fiscal Year 2027 (2027FY) with JAXA's H3 rocket. It will accommodate more than 4000 TESs focal planes reflective low-frequency and refractive medium-and-high-frequency...
We reformulate cosmological perturbations in the decaying cold dark mattermodel, and calculate microwave background anisotropies. By comparingour predictions with data from Wilkinson Microwave Anisotropy Probe, wederive a new bound on abundance lifetime of matter particles.The is constrained to ${\ensuremath{\Gamma}}^{\ensuremath{-}1}\ensuremath{\ge}123\text{ }\mathrm{G}\mathrm{y}\mathrm{r}$ at 68% C.L. (52 Gyrat 95.4% C.L.) when consists only such particles.We also consider more general...
We discuss the polarization signature of primordial gravitational waves imprinted in cosmic microwave background (CMB) anisotropies. The high-energy physics motivated by superstring theory or M-theory generically yields parity violating terms, which may produce a circularly polarized wave (GWB) during inflation. In contrast to standard prediction inflation with unpolarized GWB, GWB generates non-vanishing TB- and EB-mode power spectra CMB evaluate taking into account secondary anisotropies...
Weak lensing (WL) distortions of distant galaxy images are sensitive to neutrino masses by probing the suppression effect on clustering strengths total matter in large-scale structure. We use latest measurements WL correlations, Canada-France-Hawaii Telescope Legacy Survey data, explore constraints masses. find that, while data alone cannot place a stringent limit due parameter degeneracies, constraint can be significantly improved when combined with other cosmological probes, such as WMAP...
We derive lower bounds on intergalactic magnetic fields (IGMFs) from upper limits the pair echo emission blazar Mrk 501, that is, delayed GeV secondary e−e+ pairs produced via interactions of primary TeV gamma rays with cosmic infrared background. Utilizing only simultaneous GeV–TeV light curves observed by VERITAS, MAGIC, and Fermi Large Area Telescope during a multiwavelength campaign in 2009 included flare, are deduced IGMF strength B ≳ 10−20 G at 90% confidence level for field coherence...
We investigate bounds on the strength of primordial magnetic field (PMF) from cosmic microwave background (CMB) bispectra intensity (temperature) modes induced auto- and cross-correlated scalar tensor components PMF anisotropic stress. At first, we construct a general formula for CMB polarization PMFs composed any type perturbation. Then derive an approximate expression which traces exact shape bispectrum in order to reduce computation time with respect large number multipole configurations,...