4th BIG Meeting: Barcelona Initiative for Gravitation

Friday Nov 29, 2024, 11:30 AM → 6:30 PM Europe/Madrid

V12M (UB Physics Faculty)

 

The BIG meetings aim 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.

Organizers

Diego Blas (IFAE), Jacopo Fumagalli (ICCUB), Jaume Garriga (ICCUB), Sascha Husa (ICE-CSIC), Oriol Pujolas (IFAE), Carlos Sopuerta (ICE-CSIC)

11:30 AM → 11:45 AM Welcome and gathering

11:45 AM → 12:30 PM Constraining Primordial Black Holes with Gravitational Waves

Primordial black holes (PBHs) are hypothetical black holes that may have formed in the early Universe. They offer a rich phenomenology and are attracting attention as potential dark matter candidates. In this talk, I will discuss constraints on PBHs through gravitational wave (GW) observations, focusing on data from the LIGO-Virgo-KAGRA collaboration. One approach sets an upper bound on the stochastic GW background that could be produced in connection with PBH formation, while another examines the background generated by the superposition of numerous PBH binary events. I will also mention searches for individual GW events from PBH binaries, along with current challenges and future prospects.

Speaker: Sachiko Kuronayagi (IFT-Madrid)

BarcelonaKuroyanagi.pdf

12:30 PM → 1:00 PM Self-presentation time

We encourage everyone for a brief self-introduction

1:00 PM → 2:45 PM Lunch

2:45 PM → 3:30 PM Phase transitions in the early Universe: defects, bubbles, and gravitational waves

Cosmological phase transitions (PTs) are of interest in high energy physics as they probe energy scales that can match or even exceed the reach of current and future colliders. They are also among the loudest sources of gravitational waves (GWs) of primordial origin, thus allowing to explore new fundamental physics with GW observations. In this talk, I will give an overview of the different mechanisms driving GW production that are linked to PTs. These are associated with the dynamics of bubble nucleation and expansion during first order PTs, as well as with the formation and subsequent annihilation of topological defects. These two mechanisms can also have a non-trivial interplay in “seeded” PTs where the defects can act as impurities enhancing the nucleation rate in their vicinity, as it is the case in minimal extensions of the SM including the axion solution to the strong CP problem.

Speaker: Simone Blasi (DESY)

BIG talk.pdf

3:30 PM → 4:05 PM Neural networks and holography: gravitational duals from equations of state

Holography relates gravitational theories in five dimensions to four-dimensional quantum field theories in flat space. Under this map, the equation of state of the field theory is encoded in the black hole solutions of the gravitational theory. Solving the five-dimensional Einstein’s equations to determine the equation of state is an algorithmic, direct problem. Determining the gravitational theory that gives rise to a prescribed equation of state is a much more challenging, inverse problem. We present a novel approach to solve this problem based on physics-informed neural networks. The resulting algorithm is not only data-driven but also informed by the physics of the Einstein’s equations. We successfully apply it to theories with crossovers, first- and second-order phase transitions.

Speaker: Yago Bea (ICCUB)

BIG_Yago_Bea.pdf

4:05 PM → 5:00 PM Discussion / Break

5:00 PM → 5:35 PM Gravitational Waves from Supermassive Black Hole Binaries: Statistical Properties and Implications

Supermassive black hole binaries (SMBHBs) are anticipated to be the primary contributors to the stochastic gravitational wave background (SGWB) in the nanohertz frequency range. This talk will examine the statistical properties of the SGWB produced by SMBHBs and explore how SGWB detection informs our understanding of black hole population models and galaxy evolution.

Speaker: Xiao Xue (IFAE)

BIG_Xiao.pdf

5:35 PM → 6:10 PM Integrability in Binary Black Holes Dynamics

In this talk we discuss the presence of integrable hidden structures in the dynamics of perturbed non-rotating black holes (BHs). This can also be considered as a seed for a wider program of an effective identification of “slow” and “fast” degrees of freedom (DoFs) in the (binary) BH dynamics, following a wave-mean flow perspective. The slow DoFs would be associated with a nonlinear integrable dynamics, on which the fast ones propagate following an effective linear dynamics. BH perturbation theory offers a natural ground to test these properties. Indeed, the decoupling of Einstein equations into wave master equations with a potential provides an instance of such splitting into (frozen) slow DoFs (background potential) over which the linear dynamics of the fast ones (perturbation master functions) evolve. It has been recently shown that these wave equations possess an infinite number of symmetries that correspond to the flow of the infinite hierarchy of Korteweg-de Vries (KdV) equations. Starting from these results, we talk about the presence of integrable structures in BH perturbation theory, first in Cauchy slices and then in hyperboloidal foliations. This second step introduces a splitting of the master equation into bulk and boundary contributions, unveiling an underlying structural relation with the slow and fast DoFs. This insight represents a first step to establish the integrable structures associated to the slow DoFs as bulk symmetries of the dynamics of perturbed BHs.

Speaker: Michele Lenzi (ICE-CSIC)

4thBIG_MLenzi.pdf