São Paulo Research Group meetings in Astro & Cosmo

ICTP-SAIFR is promoting monthly one-day meetings of the São Paulo community working in the related areas of Cosmology/Astrophysics/Astroparticles/Gravity to be held at the Instituto Principia. The idea is to have a light schedule, with a couple of talks and plenty of time for discussion. The main purpose is to explore synergies of the different groups.

Next Meetings:

June 13, 2025

10:00 Ricardo Medina (UFEI): Determining self-force corrections to the equation of the separatrix of a Schwarzschild black hole

Abstract: The separatrix is the 2-dimensional curve, well known in General Relativity textbooks. It consists of a curve in the (b_c, v) plane or in the (E, j_c) plane, where b, v, E and j are respectively the impact parameter, the velocity, the dimensionless Energy and the dimensionless angular momentum of a probe particle which is subject to the gravitational field of a black hole (which, for simplicity, here we consider to be a Schwarzschild one). For a given v and b > b_c, the probe is only scattered by the black hole and it escapes to infinity but for b < b_c the probe is captured by the black hole. The situation that we consider in this talk is the (more realistic) one of a “probe” with non negligible mass, which can indeed be another black hole since the “capture case” is the one that leads to the gravitational waves that have been directly detected on Earth since 2015. Numerical results exist in the literature for this problem but in this talk we are going to expand on the analytic approach for it. We will mention the limitations and benefits of both approaches.

 

11:15 Walter Riquelme (IFT-UNESP): Imprints of Large-Scale Structures in the Anisotropies of the Cosmological Gravitational Wave Background

Abstract: In this talk, I will present recent results on the cross-correlation between the anisotropies of the cosmological gravitational wave background (CGWB) and the galaxy density contrast [2505.15899]. I will review the current state of the art and highlight the role of this cross-correlation as a tool to distinguish between different origins of the stochastic gravitational wave background. I will discuss the detection prospects of the CGWB-LSS cross-correlation signal, considering the impact of cosmic variance and the sensitivity of upcoming large-scale structure and gravitational wave surveys. Finally, I will show that, by considering a CGWB sourced by scalar-induced gravitational waves and including a scale-dependent galaxy bias, this cross-correlation could be used to measure local primordial non-Gaussianity.

 

14:00 Gustavo Figueiredo Severiano Alves (IF-USP): Chasing Serendipity: Tackling Transient Sources with Neutrino Telescopes
Abstract: The discovery of ultra-high-energy neutrinos by IceCube marked the beginning of neutrino astronomy. Yet, the origin and production mechanisms of these neutrinos remain open questions. With the recent observation of the highest-energy neutrino event to date by the KM3NeT collaboration, transient sources—astrophysical objects that emit particles in brief, localized bursts—have emerged as promising candidates. In this work, we revisit the identification of such sources in IceCube and future neutrino telescopes, focusing on how both the timing and sky localization of the source affect the detection sensitivity. We highlight the crucial role of the source’s right ascension in determining the effective area of detectors not located at the poles, such as KM3NeT, and present a framework to consistently account for this dependence. As a case study, we investigate evaporating primordial black holes (PBHs) as transient neutrino sources, showing that the detection prospects and localization accuracy are strongly influenced by the PBH’s position in the sky. Our results emphasize the complementarity between neutrino and gamma-ray observatories and showcase the potential of a global network of neutrino detectors to identify and localize transient events that might be missed by traditional photon-based instruments.