Yuichiro Tada

Inflationary primordial black holes for the LIGO gravitational wave events and pulsar timing array experiments

Primordial black holes (PBHs) are one of the candidates to explain the gravitational wave (GW) signals observed by the LIGO detectors. Among several phenomena in the early Universe, cosmic inflation is a major example to generate PBHs from large primordial density perturbations. In this paper, we discuss the possibility to interpret the observed GW events as mergers of PBHs which are produced by cosmic inflation. The primordial curvature perturbation should be large enough to produce a sizable amount of PBHs and thus we have several other probes to test this scenario. We point out that the current pulsar timing array (PTA) experiments already put severe constraints on GWs generated via the second-order effects, and that the observation of the cosmic microwave background (CMB) puts severe restriction on its

Consistent generation of magnetic fields in axion inflation models

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Primordial black holes as dark matter in supergravity inflation models

distortion. In particular, it is found that the scalar power spectrum should have a very sharp peak at

Can massive primordial black holes be produced in mild waterfall hybrid inflation

k \sim 10^{6}

Non-perturbative approach for curvature perturbations in stochastic δ N formalism

Mpc

A new algorithm for calculating the curvature perturbations in stochastic inflation

^{-1}

Primordial black holes as biased tracers

to fulfill the required abundance of PBHs while evading constraints from the PTA experiments together with the

Anisotropic CMB distortions from non-Gaussian isocurvature perturbations

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Does the detection of primordial gravitational waves exclude low energy inflation

distortion. We propose a mechanism which can realize such a sharp peak. In the future, simple inflation models that generate PBHs via almost Gaussian fluctuations could be probed/excluded.

Revisiting constraints on small scale perturbations from big-bang nucleosynthesis

There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton