title: Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914.
abstract: We point out that the gravitational-wave event GW150914 observed by the LIGO detectors can be explained by the coalescence of primordial black holes (PBHs). It is found that the expected PBH merger rate would exceed the rate estimated by the LIGO Scientific Collaboration and the Virgo Collaboration if PBHs were the dominant component of dark matter, while it can be made compatible if PBHs constitute a fraction of dark matter. Intriguingly, the abundance of PBHs required to explain the suggested lower bound on the event rate, >2  events  Gpc^{-3} yr^{-1}, roughly coincides with the existing upper limit set by the nondetection of the cosmic microwave background spectral distortion. This implies that the proposed PBH scenario may be tested in the not-too-distant future.
authors.affiliation: Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Misao
authors.initials: M
authors.lastname: Sasaki
authors.affiliation: Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Teruaki
authors.initials: T
authors.lastname: Suyama
authors.affiliation: Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan.|Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Department of Physics, Rikkyo University, Tokyo 171-8501, Japan.
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Yokoyama