A5090106018- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Particle physics theoretical and experimental studies
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Black Holes and Theoretical Physics
- Geophysics and Gravity Measurements
- Particle Detector Development and Performance
- Atomic and Subatomic Physics Research
- Solar and Space Plasma Dynamics
- Computational Physics and Python Applications
- Astronomy and Astrophysical Research
- Neutrino Physics Research
- Relativity and Gravitational Theory
- Pulsars and Gravitational Waves Research
- Scientific Research and Discoveries
- Climate variability and models
- Carbohydrate Chemistry and Synthesis
- Radio Wave Propagation Studies
- Diamond and Carbon-based Materials Research
- Geomagnetism and Paleomagnetism Studies
- Cold Fusion and Nuclear Reactions
- Stochastic processes and financial applications
- Calibration and Measurement Techniques
High Energy Accelerator Research Organization
2019-2022
Institute of Particle and Nuclear Studies
2021
The University of Tokyo
2008-2020
Institute for Basic Science
2016-2018
DTU Space
2016
University of Helsinki
2014-2016
Technical University of Denmark
2016
Helsinki Institute of Physics
2014-2016
Nagoya University
2011-2014
Kavli Institute for the Physics and Mathematics of the Universe
2010-2013
The cosmological scenario where the Peccei-Quinn symmetry is broken after inflation investigated. In this scenario, topological defects such as strings and domain walls produce a large number of axions, which contribute to cold dark matter universe. previous estimations abundance are updated refined based on field-theoretic simulations with improved grid sizes. possible uncertainties originated in numerical calculations also discussed. It found that axions can be responsible for mass range...
The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO look for axions or axion-like particles (ALPs) originating in the Sun via Primakoff conversion of solar plasma photons. In terms signal-to-noise ratio, about 4–5 orders magnitude more sensitive than CAST, currently most powerful helioscope, reaching sensitivity to axion-photon couplings down few × 10−12 GeV−1 and thus probing large fraction unexplored ALP parameter space....
We analyze the spectrum of axions radiated from collapse domain walls, which have received less attention in literature. The evolution topological defects related to axion models is investigated by performing field-theoretic lattice simulations. simulate whole process defects, including formation global strings, and annihilation due tension walls. has a peak at low frequency, implies that produced walls are not highly relativistic. revisit relic abundance cold dark matter find contribution...
We present a new mechanism for producing the correct relic abundance of dark photon matter over wide range its mass, extending down to $10^{-20}\,\mathrm{eV}$. The is initially stored in an axion which misaligned from minimum. When starts oscillating, it efficiently transfers energy into photons via tachyonic instability. If mass within few orders magnitude $m_{\gamma'}/m_a = {\cal O}(10^{-3} - 1)$, then make up dominant form today. numerical lattice simulation benchmark model that...
Cosmological evolution of axionic string network is analyzed in terms field-theoretic simulations a box 512^3 grids, which are the largest ever, using new and more efficient identification scheme global strings. The scaling parameter found to be \xi=0.87 +- 0.14 agreement with previous results. energy spectrum calculated precisely pseudo power estimator significantly reduces error mean reciprocal comoving momentum. resultant constraint on axion decay constant leads f_a <= 3*10^11 GeV. We...
We study the conditions for adiabatic resonant conversion of cold dark matter (CDM) axions into photons in astrophysically sourced strong magnetic fields such as those neutron star magnetosphere. demonstrate possibility that forthcoming radio telescopes SKA (Square Kilometre Array) can probe photon signals from CDM axions.
We consider decaying dark matter (DDM) as a resolution to the possible tension between cosmic microwave background (CMB) and weak lensing (WL) based determinations of amplitude fluctuations, σ8. perform N-body simulations in model where decays into radiation develop an accurate fitting formula for non-linear power spectrum, which enables us test DDM by combined measurements CMB, WL baryon acoustic oscillation (BAO). employ Markov chain Monte Carlo analysis examine overlap posterior...
We show that the ${H}_{0}$ tension can be resolved by making recombination occur earlier, keeping fit to cosmic microwave background (CMB) data almost intact. provide a suite of general necessary conditions give good CMB while realizing high value suggested local measurements. As concrete example for successful scenario with early recombination, we demonstrate model time-varying ${m}_{e}$ indeed satisfy all conditions. further such also well fitted low-$z$ distance measurements baryon...
We develop a formalism for studying non-Gaussianity in both curvature and isocurvature perturbations. It is shown that the perturbation between dark matter photons leaves distinct signatures cosmic microwave background temperature fluctuations, which may be confirmed future experiments, or possibly even currently available observational data. As an explicit example, we consider quantum chromodynamics axion show it can actually induce sizable inflationary scale, Hinf = O(109–1011) GeV.
We investigate the cosmological constraints on axion models where domain wall number is greater than one. In these models, multiple walls attached to strings are formed, and they survive for a long time. Their annihilation occurs due effects of explicit symmetry breaking term which might be raised by Planck-scale physics. perform three-dimensional lattice simulations compute spectra axions gravitational waves produced long-lived walls. Using numerical results, we estimated relic density...
We study the cosmological evolution of QCD axion coupled to hidden photons. For a moderately strong coupling, motion field leads an explosive production photons by tachyonic instability. use lattice simulations evaluate abundance axion. In doing so, we incorporate backreaction produced on dynamics, which becomes significant in non-linear regime. find that is suppressed at most ${\cal O}(10^{2})$ for decay constant $f_a = 10^{16}$ GeV, compared case without coupling. sufficiently large...
We derive cosmological constraints on the annihilation cross section of dark matter with velocity-dependent structure, motivated by annihilating models through Sommerfeld or Breit-Wigner enhancement mechanisms. In increasing decreasing velocity, big-bang nucleosynthesis and cosmic microwave background give stringent constraints.
Gravitational waves (GWs) are one of the key signatures cosmic strings. If GWs from strings detected in future experiments, not only their existence can be confirmed, but also properties might probed. In this paper, we study determination string parameters through direct detection GW ground-based experiments. We consider two types GWs, bursts and stochastic background, which provide us with different information about properties. Performing Fisher matrix calculation on parameters, such as...
We examine if the cosmological relaxation mechanism, which was proposed recently as a new solution to hierarchy problem, can be compatible with high reheating temperature well above weak scale. As barrier potential disappears at temperature, relaxion rolls down further after reheating, may ruin successful implementation of mechanism. It is noted that coupled dark gauge boson, frictional force arising from boson production efficiently slow motion, allows stabilized electroweak phase...
We present results of new field-theoretic simulation cosmological axion strings, which are eight times longer than previous ones. have upgraded our physical strings in Hiramatsu et al. (2011) terms the number grids as well suite analysis methods. These improvements enable us to monitor a variety quantities characterizing dynamics string network for longest term ever. Our extended simulations revealed that global do not evolve according scaling solution but its parameter, or long per horizon,...
Light scalars may be ubiquitous in nature, and their quantum fluctuations can produce large non-Gaussianity the cosmic microwave background temperature anisotropy. The accompanied with a small admixture of isocurvature perturbations, which often have correlations curvature perturbations. We present general method to calculate adiabatic perturbations without correlations, see how it works several explicit examples. also show that they leave distinct signatures on bispectrum fluctuations.
We study future observational constraints on cosmic string parameters from various types of next-generation experiments: direct detection gravitational waves (GWs), pulsar timing array, and the microwave background (CMB). consider both GW burst stochastic searches by ground- space-based interferometers as well in experiments. also contributions to CMB temperature polarization anisotropies. These different observations offer independent probes strings may enable us investigate properties if...
Light gravitinos of mass $\lesssim \mathcal{O} (10)$ eV are particular interest in cosmology, offering various baryogenesis scenarios without suffering from the cosmological gravitino problem. The may contribute considerably to total matter content Universe and affect structure formation early present epochs. After decouple other particles Universe, they free-stream consequently suppress density fluctuations (sub-)galactic length scales. Observations at relevant length-scales can be used...
The precision measurements of the cosmic microwave background power spectrum put a strong constraint on dark matter annihilation cross section since electromagnetic energy injection by affects ionization history universe. In this paper, we update our previous simulation code for calculating with effect including Helium interactions and improving calculations. We give an updated mass using modified RECFAST Planck 2018 datasets.
We update the constraint on dark matter annihilation cross section by using recent measurements of CMB anisotropy Planck satellite. fully calculate cascade products and their effects ionization, heating excitation hydrogen, hence do not rely any assumption energy fractions that cause these effects.
We propose a new constraint on millicharged dark matter from considerations galaxy clusters. The charged moves under the influence of randomly oriented magnetic fields in clusters, and corresponding density profile can significantly differ concordance CDM predictions which are well supported cluster observations. With typical amplitude $B=\mathcal O(1)\,μ$G velocity $v=\mathcal O(100)\,$km/sec at radius $R\simeq 1\,$Mpc, we claim that charge $εe$ ($e$ is elementary charge) with mass $m$...
We discuss how much we can probe the effective number of neutrino species N_nu with cosmic microwave background alone. Using data WMAP, ACBAR, CBI and BOOMERANG experiments, obtain a constraint on as 0.96< <7.94 at 95% C.L. for power-law LCDM flat universe model. The limit is improved to be 1.39 < 6.38 if assume that baryon density, helium abundance are related by big bang nucleosynthesis theory. also provide forecast PLANCK experiment using Markov chain Monte Carlo approach. In...
Decaying dark matter (DDM) is a candidate which can solve the discrepancies between predictions of concordance $\Lambda$CDM model and observations at small scales such as number counts companion galaxies Milky Way density profile center galaxies. Previous studies are limited to cases where decay particles massless and/or have almost degenerate masses with that mother particles. Here we expand DDM models so one consider arbitrary lifetime products masses. We calculate time evolutions...
The International Axion Observatory (IAXO) is a next generation axion helioscope aiming at sensitivity to the axion-photon coupling of few 10^{-12} GeV^{-1}, i.e. 1-1.5 orders magnitude beyond sensitivities achieved by currently most sensitive helioscope, CERN Solar Telescope (CAST). Crucial factors in improving for IAXO are increase magnetic field volume together with extensive use x-ray focusing optics and low background detectors, innovations already successfully tested CAST....