KEK Theory Seminar (多田　祐一郎　氏）

概要

As a long-studied astrophysical open question, it is known that almost all galaxies possess one or a few supermassive black holes (SMBHs) whose masses reach 106−9.5M⊙${10}^{6-9.5}{M}_{\odot }$ in their centers. Such SMBHs have been found even at high redshifts as z∼6−7$z\sim 6-7$ but their production mechanism is still unknown. One possible solution is the primordial black hole (PBH), which is theoretically suggested to be produced by a gravitational collapse of an overdense Hubble patch in the radiation dominant era. It has been proposed that sufficient massive PBHs can be the seeds of SMBHs. In our recent papers, we studied the possibility whether such massive PBHs can be produced in well-know hybrid inflation which is the inflation model ended by a second order phase transition. While that phase transition is roughly estimated to make large curvature perturbations enough to produce PBHs, there have been no quantitatively complete works yet because of the non-perturbative behavior around the critical point. Therefore, we proposed a non-perturbative algorithm to calculate the curvature perturbations at first, combining the stochastic and δN$\delta N$ formalism. Then we performed a wide numerical parameter search to find that PBHs are rather overproduced with the parameters which can make PBHs massive enough. In other words, we showed that massive PBHs cannot be produced with the proper abundance in hybrid inflation, without any specific assumption of the types of hybrid inflation.