Axion clouds and exotic compact objects

• Takahiro Tanaka (Kyoto U.)

Axion clouds are thought to form spontaneously around rotating black holes due to superradiance. Research is underway to find the existence of Axion by capturing traces of these clouds. Here, we discuss the influence of self-interactions and tidal interactions on the evolution of axion clouds. Furthermore, boson stars are often discussed as alternative compact objects to black holes, but its formation process is less clear. We will discuss what scenarios are possible for compact boson star formation.

The impact of gravitational wave memory in parameter estimation of massive binary black holes

• Silvia Gasparotto (IFAE)

Besides the transient effect, the passage of a gravitational wave also causes a persistent displacement in the relative position of an interferometer's test masses through the "nonlinear memory effect". This effect is generated by the gravitational backreaction of the waves themselves and encodes additional information about the source. In this talk, we present the implications of using this information for the parameter estimation of massive binary black holes with LISA. The main focus is the potential breaking of the degeneracy between the inclination and luminosity distance of the source. We also present the latest forecast of the detectability of the signal with LISA for different astrophysical models of a population of massive binary black holes.

Non-perturbative Wavefunction of the Universe in Inflation with (Resonant) features

• Vicharit Yingcharoenrat (IPMU, Tokyo)

In this talk I will first discuss a motivation why one needs to go beyond perturbation theory (PT) in inflation as going to the tail of the distribution of the primordial fluctuations. Then I will propose that the way to go beyond PT is equivalent to performing a calculation in the semi-classical limit which captures classical non-linearities at the non-perturbative level. I will move to the application of our non-perturbative method in the resonant inflationary models, in which the inflaton potential exhibits a small oscillatory modulation. As a result, given a late-time profile of the primordial fluctuations, their probability distribution function features a non-perturbative behaviors, for example, the oscillation in the late-time field value. Finally, I will show that this result can be analytically studied using the saddle-point approximation.

Towards quantum gravity constraints from S-matrix

• Katsuki Aoki (YITP, Kyoto University)

The S-matrix unitarity and causality have gained renewed interest recently in understanding the possible structures of low-energy effective field theories and quantum gravity. However, there are obstructions to applying it to gravitational EFTs due to the massless spin-2 nature of the graviton. First, I will discuss that under a certain assumption on the UV spectrum of quantum gravity, the GUT scale naturally arises from the consistency of the standard model of particle physics and general relativity. Furthermore, under the same assumption, the parameter space of dark photons is strongly constrained, ruling out the light mass range by combining theoretical and observational constraints. If I have time, I will talk about some progress for obtaining constraints on unstable states of a theory, which may be crucial to elucidating possible UV spectra of quantum gravity.