Scientific Series

Recent developments point to a remarkable resistance of black holes to tidal deformations under the influence of external gravitational fields. Relying on hidden symmetries, compelling progress has been achieved to explain that the Love numbers, characterizing tidal deformations for Kerr black holes, vanish. How does the phenomenon of tidal squeezing manifest in broader dynamical contexts? An examination of the dynamical tidal deformations in rotating black holes will be presented.

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Nonclassical causal modeling was developed in order to explain violations of Bell inequalities while adhering to relativistic causal structure and faithfulness -- that is, avoiding fine-tuned causal explanations. Recently, a no-go theorem stronger than Bell's theorem has been derived, based on extensions of Wigner's friend thought experiment: the Local Friendliness (LF) no-go theorem. Here we show that the LF no-go theorem poses formidable challenges for the field of causal modeling, even when nonclassical and/or cyclic causal explanations are considered. We first recast the LF inequalities, one of the key elements of the LF no-go theorem, as special cases of monogamy relations stemming from a statistical marginal problem; we then further recast LF inequalities as causal compatibility inequalities stemming from a nonclassical causal marginal problem, for a causal structure implied by well-motivated causal-metaphysical assumptions. We find that the LF inequalities emerge from the causal modeling perspective even when allowing the latent causes of observed events to admit post-quantum descriptions, such as Generalised Probabilistic Theories (GPT) or even more exotic theories. We further prove that no nonclassical causal model can explain violations of LF inequalities without violating the No Fine-Tuning principle. Finally, we note that these obstacles cannot be overcome even if one were to appeal to cyclic causal models.

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The Hitchin systems are a remarkable family of integrable models associated to the moduli space of principal bundles on a compact Riemann surface. In this talk, I explain how the loop group uniformization of this moduli space can be used to construct an r-matrix for the Hitchin systems. This r-matrix has been previously used in the description of the Friedan-Schenker connection on the space of conformal blocks.

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When additional degrees of freedom are considered during inflation, a crucial aspect of early universe physics emerges: the generation of isocurvature quantum fluctuations. In this talk, we will present generation and detection forecast for axionic blue-tilted isocurvature power spectra. The large blue-tilt readily evades current CMB bounds. Following a brief review, we will discuss a SUSY-embedded axion model which generates a strongly blue tilted (nI~4) isocurvature spectrum during inflation when the quantum modes are starting to be underdamped ( m/H > 3/2 ). Interestingly, there exist parametric regions with strong resonant spectral behavior that lead to rich isocurvature spectral shapes and large amplitude enhancements. These can be particularly interesting with observational consequences, in relation to the generation of PBH and GWs. The isocurvature spectral tilt is directly linked to the axion mass during inflation. Detecting blue-tilted isocurvatures can offer indirect evidence of a weakly interacting dark matter-like spectator field beyond conventional thermal-relic scenarios. Lastly, we will examine and forecast constraints for experiments such as Euclid (upcoming) and MegaMapper (proposed) using EFTofLSS based perturbative techniques. In the process we will comment upon the consistent renormalization requirements for mixed adiabatic and blue isocurvature primordial spectra.

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“Saturons" are macroscopic objects that saturate the field theoretic upper bound on microstate degeneracy. Due to their maximal microstate entropy, from a quantum information perspective, saturons and black holes belong to the same universality class with common key properties.  However, as opposed to black holes,  saturons do not require gravity and can emerge via ordinary renormalizable interactions, such as QCD, in the form  of soliton-like states. Due to this feature, saturons serve as laboratories for understanding certain properties of black holes. After reviewing the general properties of saturons, we discuss their implications for fundamental physics and cosmology. In particular, we explain how saturons can lead to a new form of phase transition. 

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Studying galaxy evolution is a human endeavour.  Simulations would ideally include physical models based on relevance, but we are often limited by practical considerations like CPU time and code complexity. I will examine energy inputs to galaxies from radiation and stellar feedback, how they are modeled in simulations, and where they are expected to influence the state of the gas and the overall evolution of a galaxy. I will focus on superbubbles (clustered supernova and stellar wind feedback) and local radiation fields, looking at the differences in what these feedbacks can do in terms of where they act in the galaxy, how that impact changes over cosmic time and how the limitations of simulations have affected our view of them.

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Jets of hadrons produced at high-energy colliders provide experimental access to the dynamics of asymptotically free quarks and gluons and their confinement into hadrons. Motivated by recent developments in conformal field theory, we show that questions of interest in collider physics can be reformulated as the study of correlation functions of a specific class of light-ray operators and their associated operator product expansion (OPE). We show that multi-point correlation functions of these operators can be measured in real collider data, allowing us to experimentally verify the scaling properties associated with the OPE, and providing new insights into the dynamics of the confinement transition.

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Carrollian holography aims to express gravity in asymptotically flat space-time in terms of a dual Carrollian CFT living at null infinity. In this talk, I will review some aspects of Carrollian holography and argue that this approach is naturally related to the AdS/CFT correspondence via a flat limit procedure. I will then introduce the notion of Carrollian amplitude, which allows to encode massless scattering amplitudes into boundary correlators, and explain its connection to celestial amplitudes. Finally, I will present recent results concerning Carrollian OPEs and deduce how soft symmetries act at null infinity.

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The theory of General Relativity has successfully passed a large number of observational tests. The theory has been extensively tested in the weak-field regime with experiments in the Solar System and observations of binary pulsars. The past 7-8 years have seen significant advancements in the study of the strong-field regime, which can now be tested with gravitational waves, X-ray data, and mm Very Long Baseline Interferometry observations. In my talk, I will summarize the state-of-the-art of the tests of General Relativity with black hole X-ray data, discussing its recent progress and future developments.

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In a complete theory of gravity we expect space-time singularities to be regularized by quantum effects. From this point of view, we have two possible regular alternatives to singular black holes (BHs) to describe the ultracompact objects that we saw in our universe: regular black holes and horizonless compact objects. I will talk about the possible structures of these black hole mimickers and the gravitational waves ringdown signal that we expect from their coalescence. In particular I will focus on the deviations in the spectrum of QNMs with respect to singular BHs, their possible detectability and the structure of echoes when backreaction effects are taken into account.

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I will summarize recent progress in uncovering the analytic structure of scattering amplitudes. The overarching theme will be exploiting new intricate ways of analytically continuing time, extending beyond the Wick rotation. I will highlight a broad range of applications: from high-precision calculations in particle physics, through computations of gravitational waves, to formal topics in the scattering of strings.

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I will talk about the boundary vertex operator algebra of topologically twisted 3d N=4 rank-zero SCFTs. The latter is recently introduced family of N=4 SCFTs with zero-dimensional Higgs and Coulomb branches, which are expected to support rational VOAs at the boundary. I will discuss the construction of the simplest class of rank-zero SCFTs T_r, and argue that they admit the simple affine VOAs L_r(osp(1|2)) at their boundary. In the simplest case, this leads to a physical realization of a novel level-rank duality between L_1(osp(1|2)) and the Virasoro minimal model M(2,5).

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