General Relativity & Quantum Cosmology

Gravitational-wave observations by LIGO and Virgo are revealing a population of merging stellar-mass binary black holes. Thus far, the broad connection between the inferred population and the physics that underlies black hole formation remains elusive. The O4a run of the LVK has more than doubled the number of binary black hole detections, and this new data is revealing new features in the population and elucidating old ones. In this talk, I survey several interesting and sometimes perplexing features and subpopulations in the population distribution. I show how they let us glean some information about the underlying formation channels and connect with transient and compact object astrophysics. As the number of detections balloons in the future, these subpopulations will be footholds to a more global understanding of binary black hole formation and the rich physics behind it. 

In the search for a consistent and renormalizable quantum theory of gravity, a conservative possibility is that gravity admits a field-theoretic description valid up to arbitrarily high energies. This amounts to going beyond the perturbative non-renormalizability of general relativity and it can be achieved following different strategies. One is to abandon Lorentz invariance as a fundamental symmetry to gain power-counting renormalizability, as in Hořava Gravity. In Asymptotically Safe Gravity, ultraviolet completeness instead arises from a non-perturbative renormalization group fixed point, preserving spacetime symmetries. In both cases, the peculiar UV structure of the theory reflects in its low-energy description, with a particular imprint on black hole physics. In this talk, I will explore these two scenarios as UV description of gravity. I will focus both on their high-energy description, reviewing some recent developments, and on the possible low-energy physics stemming from each assumption.

Neutron stars are ultra-dense remnants of massive stellar cores, observable across the electromagnetic spectrum. Their emission reflects a delicate interplay of magnetic, thermal, and structural processes under extreme conditions of density, temperature, and magnetic fields—regimes unattainable in terrestrial laboratories. Among neutron stars, magnetars stand out, hosting the strongest magnetic fields in the Universe. Their intense X-ray activity, recurrent outbursts, and unusually slow rotation point to powerful interior dynamics, yet the origin of the large-scale dipolar fields that drive their long spin periods remains a longstanding mystery. In this talk, I will introduce MATINS, a new open-access 3D code for modeling the coupled magneto-thermal evolution of isolated neutron stars. Focusing on the evolution of magnetic fields in magnetar interiors, I will discuss the key mechanisms operating under these extreme conditions, in particular the chiral magnetic effect—a phenomenon arising from the chiral anomaly that enables the conversion between magnetic helicity and electron chiral asymmetry. I will present simulations for both non-zero and vanishing initial magnetic helicity, the latter reflecting realistic conditions at the birth of a proto–neutron star. Our results show that the chiral magnetic effect can naturally transfer energy from small-scale magnetic fields at birth into the large-scale dipolar fields observed in magnetars without requiring external energy input. This provides a compelling mechanism for magnetar formation.