4th BIG Meeting: Barcelona Initiative for Gravitation

Friday 29 Nov 2024, 11:30 → 18:30 Europe/Madrid

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)

1 Welcome and gathering

2 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)

3 Self-presentation time

We encourage everyone for a brief self-introduction

13:00 Lunch

4 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)

5 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)

15:50 Discussion / Break

6 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)

7 Testing General Relativity with gravitational waves from compact binaries

Observations of gravitational waves (GWs) from compact binary mergers enable us to test General Relativity (GR) in the strong-field, highly relativistic regime. Since the breakthrough observation of the first GW signal produced by the merger of two black holes in September 2015, the number of confirmed detections has increased to nearly 100. The current observing run, O4, has already racked up more than 150 detection candidates. I will discuss a selection of tests of GR applicable to GW observations, touching upon different aspects of the generation and propagation of these signals. I will also present a brief overview of the challenges and prospects for present and future GW observatories.

Speaker: Marta Colleoni (U. Iles Balears, Palma)