| Speaker: | Luis Padilla (Rikkyo University) |
|---|---|
| Title: | Primordial Black Hole Formation during Kination: Critical Behaviour and Mass Functions |
| Date (JST): | Thu, Aug 20, 2026, 13:30 - 15:00 |
| Place: | Seminar Room A |
| Abstract: |
Primordial black holes can provide a unique probe of the matter content and expansion history of the early Universe. In this talk, I will discuss primordial black hole formation during a kination era dominated by the kinetic energy of a scalar field. Although a homogeneous massless scalar field behaves as a stiff perfect fluid at the background level, its nonlinear collapse dynamics can be significantly different. Using numerical relativity simulations in the Misner–Sharp formalism, we find that near the threshold for black hole formation the system exhibits scalar-field-like critical behaviour, including discrete self-similarity and log-periodic oscillations in the black hole mass-scaling relation. I will then discuss how this nonlinear collapse map can be incorporated into calculations of the primordial black hole mass function. In particular, I will show that discrete self-similarity can generate approximately log-periodic modulations in the mass spectrum, whose characteristic spacing is determined by the critical solution. These features are most clearly preserved for narrow primordial power spectra, while integration over a broad range of formation scales tends to wash them out. |
