| 研究実績の概要 |
(1) There is a common spectrum in the 12.5-yr data of pulsa timing array released by NANOGrav, which could be interpreted as nanohertz stochastic gravitational waves. My collaborator Guillem Domenech and I use the gravitational waves induced by scalar perturbation which reenter the horizon in an early dust-like stage to explain it. The by product is the rising of planet-mass primordial black holes, which is consistent with the recent discovery of ultra-short timescale microlensing events found in OGLE data. Our paper has been published in Sci.China Phy.Mech.Astron. 65 (2022) 3, 230411, which received much attention of the community.
(2) I helped to write a review on gravitational-wave physics, published in Sci.China Phys.Mech.Astron. 64 (2021) 12, 120401. I was on charge of the scalar-perturbation-induced gravitational wave part.
(3) Together with Misao Sasaki, we wrote a paper working on the induced gravitational wave in the non-minmal curvaton scenario, which can increase the curvature perturbation on a small scale to generate primordial black holes (e.g. as all the dark matter). The generation will be greatly enhanced by the non-Gaussianity of the curvature perturbation. For the first time, we calculate the primordial black hole abundance taking into account the full nonlinear effects. Interestingly, we found that in the large non-Gaussian limit the curvature perturbation can be well approximated by a quadratic form, while in the moderate non-Gaussian case the curvature perturbation has the same logarithmic form as that of the ultra-slow-roll inflation.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
As is written in the plan, the project is to find the energy spectrum of stochastic gravitational waves, which can be used to distinguish them in the inteferometers. My research this year has found a new spectral shape of the scalar-perturbation induced gravitational wave, i.e. the one from non-minimal curvaton scenario. The non-Gaussian limit of this model is distinguishable with other induced gravitational waves, as its ultraviolet behavior has some characteristic features.
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| 今後の研究の推進方策 |
This year I will focus on the ultra-slow-roll inflation, which can enhance the scalar power spectrum thus induce substantial gravitational waves. The energy spctrum from the ultra-slow-roll inflation seems to have some universal features which is now not very well appreciated by the community. By extract the key essence of such models, I will try to find such features, which can help us to distinguish such a physical mechanism in the spectral shape of the gravitational wave.
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