Kazunori Kohri

Whether or not the primordial gravitational wave (GW) produced during inflation is sufficiently strong to be observable, GWs are necessarily produced from the primordial curvature perturbations in the second order of perturbation. The induced GWs can be enhanced by curvature perturbations enhanced at small scales or by the presence of matter-dominated stages of the cosmological history. We analytically calculate the integral in the expression of the power spectrum of the induced GWs, which is a

The chemical nature of urinary stone protein is poorly understood. We have sequenced a cDNA of urinary calcium oxalate stone protein extracted with EDTA. cDNA sequences showed complete identity between urinary stone protein and human osteopontin. Osteopontin protein was detected by staining with Stains-All, which specifically stains phosphoproteins, and by digestion with the highly specific protease thrombin, demonstrating that urinary calcium oxalate stones consist of osteopontin protein. We us

We study the effects of unstable gravitino on big-bang nucleosynthesis. If the gravitino mass is smaller than $\ensuremath{\sim}10\text{ }\text{ }\mathrm{TeV}$, primordial gravitinos produced after inflation are likely to decay after big-bang nucleosynthesis starts, and light-element abundances may be significantly affected by hadro and photodissociation processes as well as by $p\ensuremath{\leftrightarrow}n$ conversion process. We calculate the light-element abundances and derive upper bounds

It is often considered that a massive torus with solar mass or so surrounding a stellar-mass black hole may be a central engine of a gamma-ray burst. We study the properties of such massive accretion tori (or disks) based on the $\alpha$ viscosity model. For surface density exceeding about $10^{20}$ g cm$^{-2}$, which realizes when about a solar-mass material is contained within a disk with a size of $\sim 5 \times 10^6$ cm, we find that (1) luminosity of photons is practically zero due to signi

The NANOGrav collaboration for the pulsar timing array (PTA) observation recently announced evidence of an isotropic stochastic process, which may be the first detection of the stochastic gravitational-wave (GW) background. We discuss the possibility that the signal is caused by the second-order GWs associated with the formation of solar-mass primordial black holes (PBHs). This possibility can be tested by future interferometer-type GW observations targeting the stochastic GWs from merger events

Supermassive black holes and intermediate mass black holes are believed to exist in the Universe. There is no established astrophysical explanation for their origin, and considerations have been made in the literature that those massive black holes (MBHs) may be primordial black holes (PBHs), black holes which are formed in the early universe (well before the matter-radiation equality) due to the direct collapse of primordial overdensities. This paper aims at discussing the possibility of exclud

We consider big bang nucleosynthesis (BBN) with long-lived charged massive particles. Before decaying, the long-lived charged particle recombines with a light element to form a bound state like a hydrogen atom. This effect modifies the nuclear-reaction rates during the BBN epoch through the modifications of the Coulomb field and the kinematics of the captured light elements, which can change the light element abundances. It is possible for heavier nuclei abundances such as $^{7}\mathrm{Li}$ and