Date: August 11, 2026
Venue: IAFE Auditorium, Institute of Astronomy and Space Physics (CONICET-UBA). IAFE Building, Ciudad Universitaria, CABA - Argentina.
PROGRAM
10:30–11:30: Federico Huxhagen (DF-UBA)
Title: “Searching for ultralight dark matter through binary pulsar timing data”
Abstract: A well-motivated possibility to explain the nature of dark matter is that it is composed of ultralight bosons, and can therefore be effectively described as a field undergoing oscillations at its Compton frequency. In particular, in the lower region of the mass spectrum, these oscillations can develop coherently over decades, leaving imprints on high-precision astrophysical experiments. In this context, binary pulsars act as powerful probes to study these ultralight dark matter candidates. In this talk, we will describe how the field perturbs the orbits of the binary systems under study, inducing variations in the pulse times of arrival at Earth. In addition, we present the exclusion limits obtained from the analysis of binary pulsar timing data, exploring regions of parameter space that are inaccessible to other astrophysical probes.
11:30–12:00: Coffee break
12:00–13:00: Valentina Crespi (IALP)
Title: “Fermionic dark matter: applications on galactic scales”
Abstract: The nature and composition of dark matter remain among the greatest open questions in modern cosmology. In this talk, we will explore the fermionic dark matter paradigm within the Ruffini-Argüelles-Rueda (RAR) model for galactic halos. In this framework, particles in the keV mass range naturally generate, from first principles, density profiles with a characteristic dense-core/extended-halo structure. We will present applications of this model using different tracers of the gravitational potential across a range of galactic scales. The results show that current astrophysical observables make it possible to constrain both the mass and the parameter space of these dark matter particles.
13:00–14:00: Lunch
14:00–15:00: Agustina Pereyra Grau (IAFE)
Title: “Hidden symmetries in compactified gravity theories”
Abstract: The effective action of string theory admits an expansion in powers of the parameter α′, whose leading term is supergravity and whose successive orders involve an increasing number of derivatives. Since these theories are formulated in ten or eleven dimensions, describing physics in four dimensions requires compactifying the remaining ones, a procedure in which some symmetries are preserved, others are broken, and new symmetries emerge. In this talk, I will show that a class of diffeomorphisms that compactification appears to break actually survives as a global symmetry of the reduced theory, giving rise to a principle that strongly constrains the effective action and allows one to predict α′ corrections.
15:00–15:30: Coffee break
15:30–16:30: Nicolás Yunes (University of Illinois Urbana-Champaign)
Title: “The sound of a merger: quasinormal modes and gravity beyond Einstein”
Abstract: Gravitational waves allow us to study black holes as dynamical objects, not only as stationary solutions of Einstein’s equations. In this talk, I will introduce the relaxation phase following a merger, known as the ringdown, and explain why its structure is governed by quasinormal modes: the characteristic “notes” through which a perturbed black hole returns to equilibrium.
After presenting the basic idea, I will discuss what general relativity predicts for these modes and what is required to use the ringdown as a test of strong-field gravity. The main focus will be on how to extend this program beyond general relativity: what changes when the gravitational dynamics, the perturbation equations, or the boundary conditions are modified, and which observables could distinguish among these possibilities. I will conclude by connecting this modal description with the gravitational-wave signal itself, showing how different parts of the waveform encode complementary information about the nature of black holes and gravity.