We show that highly spinning primordial black holes of mass $M\sim 10^{12}$ kg, potentially born in a matter-dominated era after inflation, can produce clouds of pions in their vicinity via the superradiant instability, with densities up to that of nuclear matter. We discuss the electromagnetic signatures of this process, via neutral pion decay and charged pion annihilation into photons, computing in particular their contribution to the isotropic gamma-ray background. This allows us to place upper bounds on the abundance of such primordial black holes that are comparable to the ones obtained from Hawking evaporation. We also discuss the possibility of directly observing such clouds in high-redshift superclusters.
The superradiant instability can lead to the generation of extremely dense axion clouds around rotating black holes. We show that, despite the long lifetime of the QCD axion with respect to spontaneous decay into photon pairs, stimulated decay becomes significant above a minimum axion density and leads to extremely bright lasers. The lasing threshold can be attained for axion masses $μ\gtrsim 10^{-8}\ \mathrm{eV}$, which implies superradiant instabilities around spinning primordial black holes with mass $\lesssim 0.01M_\odot$. Although the latter are expected to be non-rotating at formation, a…
Dark radiation from Kerr primordial black holes: the role of superradiance
College of Sciences, Northeastern University（东北大学理学院）；Liaoning Key Laboratory of Cosmology and Astrophysics（辽宁省宇宙学与天体物理重点实验室）；MOE Key Laboratory of Data Analytics and Optimization for Smart Industry（教育部智能工业数据分析与优化重点实验室）；National Frontiers Science Center for Industrial Intelligence and Systems Optimization（国家工业智能与系统优化前沿科学中心）
String Axiverse Enhancement of Superradiant Dark Matter Production
University of Groningen（格罗宁根大学）；Faculdade de Ciências e Tecnologia da Universidade de Coimbra（科英布拉大学科学与技术学院）；Centro de Física da Universidade de Coimbra（科英布拉大学物理中心）；Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto（波尔图大学理学院天体物理学系）
Institute for Nuclear Research of the Russian Academy of Sciences（俄罗斯科学院核物理研究所）；National Research Nuclear University MEPhI（国立核研究大学莫斯科工程物理学院）；Sternberg Astronomical Institute, Lomonosov Moscow State University（莫斯科罗蒙诺索夫国立大学斯捷尔伯格天文学研究所）
We consider the imprint of superradiant instabilities of nonevaporating primordial black holes (PBHs) on the spectrum of the cosmic microwave background (CMB). In the radiation dominated era, PBHs are surrounded by a roughly homogeneous cosmic plasma which endows photons with an effective mass through the plasma frequency. In this setting, spinning PBHs are unstable to a spontaneous spindown through the well-known "black-hole bomb" mechanism. At linear level, the photon density is trapped by the effective photon mass and grows exponentially in time due to superradiance. As the plasma density d…
We show that in a pioneering paper by Polnarev and Zembowicz, some conclusions concerning the characteristics of the Turok-strings are generally not correct. In addition we show that the probability of string collapse given there, is off by a large prefactor (~1000).
The mass distribution of Primordial Black Holes (PBHs) is affected by drops in the pressure of the early Universe plasma. For example, events in the standard model of particle physics, such as the $W^\pm/Z^0$ decoupling, the quark-hadron transition, the muon and pion becoming non-relativistic, and the annihilation of electrons and positrons, cause a suppression in the Equation of State parameter and leave peaks in the PBH mass function around $10^{-6},\,2,\,60$, and $10^6\, M_\odot$, respectively, in the case of a nearly scale-invariant primordial power spectrum. The superposition of unresolve…
We consider a superradiance effect around rotating dilatonic black holes. We analyze two cases: one is an exact solution with the coupling constant $α=\sqrt{3}$, which effective action is reduced from the 5-dimensional Kaluza-Klein theory, and the other is a slowly rotating dilatonic black holes with arbitrary coupling constant. We find that there exists a critical value ($α\sim 1$), which is predicted from a superstring model, and the superradiant emission rate with coupling larger than the critical value becomes much higher than the Kerr-Newman case ($α=0$) in the maximally charged limit. Co…
Enlightening dark moments of neutrino with superradiance
Institute of Mathematical Sciences, HBNI（数学科学研究所，HBNI）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Indian Institute of Science Education and Research Berhampur（贝赫拉普尔印度科学教育研究学院）
We consider the evolution of a cosmic string loop that is captured by a much more massive and compact black hole. We show that after several reconnections that produce ejections of smaller loops, the loop that remains bound to the black hole moves on a nearly-periodic non-self-intersecting trajectory, "the orbit". The orbit evolves due to an energy and angular momentum exchange between the loop and the spinning black hole. We show that such evolution is mathematically equivalent to a certain continuous deformation of an auxiliary closed curve in a 3-dimensional space; for zero black-hole spin …
Stephen Hawking's contributions to the understanding of gravity, black holes and cosmology were truly immense. They began with the singularity theorems in the 1960s followed by his discovery that black holes have an entropy and consequently a finite temperature. Black holes were predicted to emit thermal radiation, what is now called Hawking radiation. He pioneered the study of primordial black holes and their potential role in cosmology. His organisation of and contributions to the Nuffield Workshop in 1982 consolidated the picture that the large-scale structure of the universe originated as …
Black Holes, Gravitational Waves and Space-Time Singularities Lemaitre Conference 2024
Università di Roma ‘Tor Vergata’（罗马托尔维尔加塔大学）；INFN, Sezione di Roma Tor Vergata（罗马托尔维尔加塔意大利国家核物理研究所）；DiSAT, Università dell’Insubria（因苏布里亚大学 DiSAT 学院）；INFN, Sezione di Milano（米兰意大利国家核物理研究所）；Como Lake centre for AstroPhysics (CLAP)（科莫湖天体物理中心）；Vatican Observatory（梵蒂冈天文台）；INAF/OAS Bologna（博洛尼亚意大利国家天体物理研究所观测天文学与天体物理学部门）；INFN, Sezione di Bologna（博洛尼亚意大利国家核物理研究所）；Laboratori Nazionali di Frascati, INFN（弗拉斯卡蒂意大利国家核物理研究所）；Dipartimento di Matematica, Politecnico di Milano（米兰理工大学数学系）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）
