Misao Sasaki – författare

Early Universe cosmology is an active area of research and cosmic inflation is a pillar of modern cosmology. Among predictions of inflation, observationally the most important one is the generation of cosmological perturbations from quantum vacuum fluctuations that source all inhomogeneous structures in the Universe, not to mention the large-scale structures such as clusters of galaxies.Cosmological perturbation theory is the basic tool to study the perturbations generated from inflation. There are a few different approaches to primordial cosmological perturbations. In the conventional approach one perturbs the field equations and after quantizing the perturbations by the use of the corresponding action, one calculates the power spectrum of cosmological observables. This approach extends to higher order perturbations such as bispectrum etc., but the analysis becomes increasingly difficult.The delta N formalism, the topic of this book, is an alternative approach. The novelty of this approach is that, under the condition that the scale of interest is very large so that the spatial derivatives may be ignored in the dynamics, it can be applied to all orders in perturbation theory and has a rigorous foundation in general relativity. Thanks to the fact that one can evaluate perturbations with only the knowledge of background solutions, it is proved to be much easier than the conventional approach in evaluating higher order effects in many cases.

Primordial black holes (PBHs) were proposed more than 50 years ago as black holes possibly formed across a vast mass range in the early universe. They represent a unique probe to access the primordial universe and cosmological inflation. Furthermore, in certain mass ranges, they could comprise the entirety of the dark matter, seed supermassive black holes at high redshift, be responsible for some gravitational-wave events detected so far, and be novel gravitational-wave sources detectable with future instruments. However, detecting PBHs has proved to be extremely challenging and extensive research focused on setting a variety of constraints on the fraction of dark matter composed by these objects. This book highlights an up-to-date, comprehensive overview on this subject, including pedagogical details on the PBH formation scenarios, cosmological evolution, astrophysical implications, connections with gravitational-wave astronomy, and critical discussion of the latest and future constraints. At variance with all existing reviews on this subject, this book addresses graduate students and researchers not necessarily familiar with all areas of the topic, providing details on important key results rather than collecting and reviewing the latest literature. The topic is naturally interdisciplinary and connects areas as diverse as cosmology, particle physics, gravitational-wave astronomy, and numerical simulations. To reflect this diversity, the book includes 25 contributions from key researchers working in these different areas. It provides a unique reference both to approach the topic for the first time and to learn a specific specialized sub-area.