231 citations · 1.9k across the 26 of their papers we have counts for
26 papers
Gravitational waves from binary black holes as probes of the structure formation history
Tomohiro Nakama
Gravitational-wave detectors on earth have detected gravitational waves from merging compact objects in the local Universe. In future we will detect gravitational waves from higher…
A gigaparsec-scale local void and the Hubble tension
Qianhang Ding, Tomohiro Nakama, Yi Wang
We explore the possibility of using a gigaparsec-scale local void to reconcile the Hubble tension. Such a gigaparsec-scale void can be produced by multi-stream inflation where diff…
Ultracompact minihalos associated with stellar-mass primordial black holes
Tomohiro Nakama, Kazunori Kohri, Joseph Silk
The possibility that primordial black hole binary mergers of stellar mass can explain the signals detected by the gravitational-wave interferometers has attracted much attention. I…
Spectral Distortions of the CMB as a Probe of Inflation, Recombination, Structure Formation and Particle Physics
J. Chluba, A. Kogut, S. P. Patil +98
Following the pioneering observations with COBE in the early 1990s, studies of the cosmic microwave background (CMB) have focused on temperature and polarization anisotropies. CMB…
Enhancement of Gravitational Waves Induced by Scalar Perturbations due to a Sudden Transition from an Early Matter Era to the Radiation Era
Keisuke Inomata, Kazunori Kohri, Tomohiro Nakama +1
We study gravitational waves induced from the primordial scalar perturbations at second order around the reheating of the Universe. We consider reheating scenarios in which a trans…
Gravitational Waves Induced by Scalar Perturbations during a Gradual Transition from an Early Matter Era to the Radiation Era
Keisuke Inomata, Kazunori Kohri, Tomohiro Nakama +1
We revisit the effects of an early matter-dominated era on gravitational waves induced by scalar perturbations. We carefully take into account the evolution of the gravitational po…
Gravitational Production of Superheavy Dark Matter and Associated Cosmological Signatures
Lingfeng Li, Tomohiro Nakama, Chon Man Sou +2
We study the gravitational production of super-Hubble-mass dark matter in the very early universe. We first review the simplest scenario where dark matter is produced mainly during…
Detectability of Gravitational Waves from the Coalescence of Massive Primordial Black Holes with Initial Clustering
Qianhang Ding, Tomohiro Nakama, Joseph Silk +1
We show that the effect of initial non-Gaussian clustering can significantly enhance the event rate for primordial black hole (PBH) coalescence. The impact of such clustering is st…
Gravitational waves induced by scalar perturbations as probes of the small-scale primordial spectrum
Keisuke Inomata, Tomohiro Nakama
Compared to primordial perturbations on large scales, roughly larger than megaparsec, those on smaller scales are not severely constrained. We revisit the issue of probing smal…
Micro black holes formed in the early Universe and their cosmological implications
Tomohiro Nakama, Jun'ichi Yokoyama
High energy collisions of particles may have created tiny black holes in the early Universe, which might leave stable remnants instead of fully evaporating as a result of Hawking r…
Do we need fine-tuning to create primordial black holes?
Tomohiro Nakama, Yi Wang
Recently, the formation of primordial black holes (PBHs) from the collapse of primordial fluctuations has received much attention. The abundance of PBHs formed during radiation dom…
Reheating through the Higgs amplified by spinodal instabilities and gravitational creation of gravitons
Tomohiro Nakama, Jun'ichi Yokoyama
It is shown that a positive non-minimal coupling of the Higgs field to gravity can solve the two problems in inflation models in which postinflationary universe is dominated by an…
Constraints on small-scale primordial power by annihilation signals from extragalactic dark matter minihalos
Tomohiro Nakama, Teruaki Suyama, Kazunori Kohri +1
We revisit constraints on small-scale primordial power from annihilation signals from dark matter minihalos. Using gamma rays and neutrinos from extragalactic minihalos and assumin…
Limits on primordial black holes from distortions in cosmic microwave background
Tomohiro Nakama, Bernard Carr, Joseph Silk
If primordial black holes (PBHs) form directly from inhomogeneities in the early Universe, then the number in the mass range is severely constrained by upp…
Shedding light on the small-scale crisis with CMB spectral distortions
Tomohiro Nakama, Jens Chluba, Marc Kamionkowski
The small-scale crisis, discrepancies between observations and N-body simulations, may imply suppressed matter fluctuations on subgalactic distance scales. Such a suppression could…
Stochastic gravitational waves associated with the formation of primordial black holes
Tomohiro Nakama, Joseph Silk, Marc Kamionkowski
Primordial black hole (PBH) mergers have been proposed as an explanation for the gravitational wave events detected by the LIGO collaboration. Such PBHs may be formed in the early…
Supermassive black holes formed by direct collapse of inflationary perturbations
Tomohiro Nakama, Teruaki Suyama, Jun'ichi Yokoyama
We propose a mechanism of producing a new type of primordial perturbations that collapse to primordial black holes whose mass can be as large as necessary for them to grow to the s…
Primordial black holes as a novel probe of primordial gravitational waves. II: Detailed analysis
Tomohiro Nakama, Teruaki Suyama
Recently we have proposed a novel method to probe primordial gravitational waves from upper bounds on the abundance of primordial black holes (PBHs). When the amplitude of primordi…
Primordial black holes as a novel probe of primordial gravitational waves
Tomohiro Nakama, Teruaki Suyama
We propose a novel method to probe primordial gravitational waves by means of primordial black holes (PBHs). When the amplitude of primordial tensor perturbations on comoving scale…
Cosmological long-wavelength solutions and primordial black hole formation
Tomohiro Harada, Chul-Moon Yoo, Tomohiro Nakama +1
We construct cosmological long-wavelength solutions without symmetry in general gauge conditions compatible with the long-wavelength scheme. We then specify the relationship among…
The double formation of primordial black holes
Tomohiro Nakama
Primordial black holes (PBHs) are a useful tool in cosmology to probe primordial inhomogeneities on small scales that reenter the Hubble radius during the radiation dominated epoch…
Testing scenarios of primordial black holes being the seeds of supermassive black holes by ultracompact minihalos and CMB -distortions
Kazunori Kohri, Tomohiro Nakama, Teruaki Suyama
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 considerati…
Reheating the Universe Once More: The Dissipation of Acoustic Waves as a Novel Probe of Primordial Inhomogeneities on Even Smaller Scales
Tomohiro Nakama, Teruaki Suyama, Jun'ichi Yokoyama
We provide a simple but robust bound on the primordial curvature perturbation in the range , which has not been constrained so far un…
Investigating formation condition of primordial black holes for generalized initial perturbation profiles
Tomohiro Nakama, Tomohiro Harada, A. G. Polnarev +1
Primordial black holes (PBHs) are an important tool in cosmology to probe the primordial spectrum of small-scale curvature perturbations that reenter the cosmological horizon durin…