BIG&C Meetings: Barcelona Initiative for Gravitation and Cosmology

Monday 18 Sept 2023, 12:00 → 18:30 Europe/Madrid

UB Physics Faculty

 

The BIG&C (Barcelona Initiative for Gravitation and Cosmology) aims to bring together all actors working in the field of gravity and cosmology in Barcelona, from observations to theory. 

These series of meetings has the purpose to set an informal stage for the exchange of ideas and to encourage joint discussions on relevant topics in the field.  It also provides the opportunity for people working in Barcelona to get informed on the lines of research of the other institutes.

1st kick off event: 18th September, 2023 at ICCUB, Aula Pere Pascual

Organizers

Diego Blas (IFAE), Jacopo Fumagalli (ICCUB), Jaume Garriga (ICCUB), Cristiano Germani (ICCUB), Oriol Pujolas (IFAE), Carlos Sopuerta (ICE-CSIC/IEEC)

1 Axion clouds and exotic compact objects

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.

Speaker: Takahiro Tanaka (Kyoto U.)

13:00 Lunch

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

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.

Speaker: Silvia Gasparotto (IFAE)

15:15 Break

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

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.

Speaker: Vicharit Yingcharoenrat (IPMU, Tokyo)

16:15 Discussion / Break

4 Towards quantum gravity constraints from S-matrix

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.

Speaker: Katsuki Aoki (YITP, Kyoto University)