## Title: *Formation and Evolution of Primordial Black Hole Binaries in the Early Universe*
## Reporter: Jia-Ning Wang
| 11.11| 10.00 AM | 6420 | Wang-Wei Yu |
## Title: *Implications for the Hubble tension from the ages of the oldest astrophysical objects*
## Reporter: Wang-Wei Yu
## Abstract
The abundance of primordial black holes (PBHs) in the mass range 0.1~1000 M _{sun} can potentially be tested by gravitational wave observations due to the large merger rate of PBH binaries formed in the early universe. To put the estimates of the latter on a firmer footing, we first derive analytical PBH merger rate for general PBH mass functions while imposing a minimal initial comoving distance between the binary and the PBH nearest to it, in order to pick only initial configurations where the binary would not get disrupted. We then study the formation and evolution of PBH binaries before recombination by performing N-body simulations. We find that the analytical estimate based on the tidally perturbed 2-body system strongly overestimates the present merger rate when PBHs comprise all dark matter, as most initial binaries are disrupted by the surrounding PBHs. This is mostly due to the formation of compact N-body systems at matter-radiation equality. However, if PBHs
make up a small fraction of the dark matter, these estimates become more
reliable. In that case, the merger rate observed by LIGO imposes the strongest constraint on the PBH abundance. Finally, we argue that, even if most
initial PBH binaries are perturbed, the present BH-BH merger rate of binaries formed in the early universe is larger than O(10)Gpc^{−3} yr^{−1} f^3
_{PBH}.
In the Journal Club, I want to share a paper named *Implications for the Hubble tension from the ages of the oldest astrophysical objects* written by *Sunny Vagnozzi* et al. I will explain why the Hubble tension will only be solved using the early physics and late physics togther according to the paper. I will introduce the old astrophysical objects data and what we can do by using the data.
## References
-[Arxiv:1812.01930](https://arxiv.org/abs/1812.01930)*Formation and Evolution of Primordial Black Hole Binaries in the Early Universe* by *Martti Raidal* at al.
-[Arxiv:2105.10421](https://arxiv.org/abs/2105.10421)*Implications for the Hubble tension from the ages of the oldest astrophysical objects* by *Sunny Vagnozzi* at al.
## Title: *Back-reaction on inflationary model with parametric resonance*
## Reporter: Zhi-Zhang Peng
| 11.11 | 2.30 PM | 6420 | Cheng-Hu Ge |
## Title: *Interior Structure of Anisotropic Black Holes with Charged Vector Hairs*
## Reporter: Cheng-Hu Ge
## Abstract
In this group seminar, I will introduce the parameterization of inflationary model with resonant amplification of perturbations and briefly discuss the back-reaction of perturbations.
In this work, we establish a no inner-horizon theorem for black holes with charged vector hairs. Firstly, introducing a free charged vector field into the Einstein-Maxwell theory with a negative cosmological constant, by constructing a radially conserved charged, we prove that there is no
Cauchy horizon for black holes with charged vector hairs. According to numerical results, we
obtain asymptotic behaviors of metric and matter fields near the singularity and show that
the geometry near the singularity presents anisotropic Kasner epochs, Kasner complements
and Kasner opposite. Considering metric and matter field ansatz, we numerically solve holographic P-wave superconductor to illustrate that when the charge vector field in space-time is very weak (i.e. the black hole temperature is close to the critical temperature) nonlinear dynamics occur inside the black hole. These include Collapse of the Einstein-Rosen bridge, Josephson oscillation and oscillation of the x component of metric gxx. We also obtain the equation solutions of anisotropic factor u and charged vector field ρµ in the oscillation regime. Finally, we extend the no inner-horizon theorem to the case of the general potential field and the modified gravity with the Gauss-Bonnet term.
## References
<!-- - [Arxiv:2101.01282](https://arxiv.org/abs/2101.01282)*A cuspy dark matter halo* by *Yong Shi* et al.
-[Arxiv:2109.01402](https://arxiv.org/abs/2109.01402)*A shallow dark matter halo in Ultra Diffuse Galaxy AGC 242019: are UDGs structurally similar to low surface brightness galaxies?* by *Chris B.Brook* et al. -->
