The University of Tokyo · 물리·천문학
요코야마 준이치 교수의 연구실은 초기 우주에서 형성된 초기 블랙홀, 특히 원시 블랙홀(PBHs)의 생성 메커니즘과 그 우주론적 영향을 중심으로 연구를 이어가고 있습니다. 특히 인플레이션 이론과 밀접하게 연결된 밀도 불안정성의 진화, 비선형 중력 수축을 통한 PBH 형성 조건, 그리고 다양한 천체물리적 관측 제약과의 비교 분석을 통해 PBH의 질량 스펙트럼과 우주에서의 기여도를 규명하고자 합니다. 이는 블랙홀의 기원뿐 아니라 암흑물질의 후보로 제시되는 PBH의 존재 가능성에 대한 핵심적인 이론적 기초를 제공합니다.
표시된 성과는 수집된 데이터 기준으로 산출되며, 일부 차이가 있을 수 있습니다.
It is shown that in a number of scalar potentials with an unstable local maximum at the origin chaotic inflation is followed by new inflation if model parameters are appropriately chosen. In this model density fluctuation can have a large-amplitude peak on the comoving Hubble scale at the onset of the slow-roll new inflation and can result in the formation of an appreciable amount of primordial black holes on astrophysically interesting mass scales.
We show that it is extremely difficult and perhaps even impossible to have inflation supported by thermal effects.
The mass function of primordial black holes created through the near-critical gravitational collapse is calculated in a manner fairly independent of the statistical distribution of underlying density fluctuation, assuming that it has a sharp peak on a specific scale. Comparing it with various cosmological constraints on their mass spectrum, some newly excluded range is found in the volume fraction of the region collapsing into black holes as a function of the horizon mass.
The spectrum of curvature perturbation generated during inflation is studied in the case the inflation-driving scalar field (inflaton) φ crosses over its potential extremum. It is shown that the nondecaying mode of perturbation has a finite value and a proper formula is given. The result is also extended to more general cases where φ̈ is nonnegligible.
We update the constraints on the fraction of the Universe that may have gone into primordial black holes (PBHs) over the mass range 10<sup>-5</sup>to 10<sup>50</sup> g. Those smaller than ∼10<sup>15</sup> g would have evaporated by now due to Hawking radiation, so their abundance at formation is constrained by the effects of evaporated particles on big bang nucleosynthesis, the cosmic microwave background (CMB), the Galactic and extragalactic<i>γ</i>-ray and cosmic ray backgrounds and the possib
As a nonbaryonic explanation of massive compact halo objects, a phenomenological model is presented which predicts formation of primordial black holes at a desired mass scale. The required feature of initial density fluctuation is realized making use of the primordially isocurvature fluctuation generated in an inflationary universe model with multiple scalar fields.
A new scenario of cosmic strings is presented which is free from the gravitational-radiation constraints imposed on their line density by the primordial nucleosynthesis and the timing data of a millisecond pulsar. In this scenario the phase transition is induced nonthermally during the inflation so that it is not necessary to assume Friedmann-Robertson-Walker universe in thermal equilibrium at the outset.
