Ph.D. Theses

This thesis provides new non-perturbative numerical methods and exact analytic constructions in the context of low-dimensional conformal field theory and holography.The main results are a six-point extension of the numerical conformal bootstrap and the identification of the holographic dual of anti-de Sitter (AdS) D-branes in minimal pure NSNS AdS$_3$.On the numerical side, the thesis introduces a six-point bootstrap framework that exploits positivity in decompositions of six-point correlation functions into products of four-point correlators to derive rigorous bounds on solutions to six-point crossing equations.The resulting optimisation problem involves semi-definite programming (SDP) with infinite-dimensional constraint matrices.By employing sparse SDP techniques, the problem is recast into a numerically tractable form.As a proof of concept, the method is implemented for conformally invariant correlation functions in one dimension, providing e.g.~a non-perturbative handle on correlations of holographic boundary modes in interacting quantum field theories defined on AdS$_2$.On the analytic side, the thesis introduces a family of one-dimensional holographic interfaces between symmetric product orbifolds.These interfaces are first analysed algebraically via explicit boundary states in the folded theory.In this framework, the partition function of interface-changing operators is computed and exactly matched with the annulus partition function of AdS$_2$ branes in the Eberhardt–Gaberdiel–Gopa\-kumar tensionless limit of superstring theory on pure NSNS AdS$_3 \times S_3 \times \mathbb{T}^4$.Finally, an alternative description of the interfaces in terms of a novel class of generalised covering maps is provided, which yields significantly improved control over interface correlators and higher-genus partition functions.With this new handle on the interface correlators, a 't Hooft-like expansion is established which structurally matches string perturbation theory to all orders in the string coupling..

Despite the Standard Model's ability to describe collider data from all experiments conducted around the world, several questions about the history of the Universe, including the hierarchy problem, the baryon asymmetry, and the dark matter density, remain open. To address these unresolved issues, the particle physics community agrees on the need to construct a next-generation collider that could probe the Standard Model with higher accuracy and potentially reveal deviations from the predictions of this fundamental theory. [...]

In this thesis, a comprehensive investigation of the electronic energy structureand associated radiation- and photostimulated processes in a wide class of perovskite-based scintillation materials is presented. The research encompasses the study ofinorganic crystals Cs₂MCl₆ (M = Hf, Zr), CsPbX₃ (X = Cl, Br, I), as well as organic-inorganic perovskites with the general formula MAPbX₃ (X = Cl, Br, I).The crystal structure of inorganic Cs₂HfCl₆ and Cs₂ZrCl₆ perovskites wasinvestigated. [...]

This thesis investigates the interplay between integrability, defects, and renormal-ization group (RG) flows, in quantum field theories in 2 and 4 dimensions.In the first part, we study the analytic properties and integrable structure of the meson spectrum in the large Nc limit of two-dimensional QCD. In this regime, the integral equation governing meson masses is shown to be equivalent to a TQ-Baxter equation, characteristic of integrable models. [...]

Modulation-based X-ray microtomography is an emerging technique that simultaneously reconstructs three-dimensional maps of attenuation, phase shift, and small-angle scattering from a sample. The complementarity of these signals enables quantitative insights into the sample's composition that no single contrast modality can provide alone. [...]

Direct imaging chemical reactions with atomic-scale spatial resolution and femtosecond-to-attosecond temporal precision is long seeking goal to better understand molecular chemistry. This vision, called "molecular movie'' is a direct step for understanding of molecule dynamics and reactivity during isomerization, bond breaking and reformation, and photocatalytic reactions. [...]

Compact electron accelerators powered by laser-generated terahertz (THz) radiation have the potential to enable novel laboratory-scale X-ray sources. Accelerating electrons to highly relativistic energies in dielectric-loaded waveguides requires narrowband THz pulses at frequencies between 0.1 and 0.5 THz with pulse energies of several millijoules. [...]

We extend the study of black hole superradiance in binary systems, also known as gravitational atomic physics, to include eccentric and inclined orbits. Such systems exhibit Landau-Zener-like transitions between bound states of the bosonic cloud. [...]

Searches for physics beyond the Standard Model can be pursued through high-precision measurements of atomic systems that are sensitive to variations in fundamental constants. In this thesis, highly charged ions (HCI) are investigated as promising candidates for optical clocks to probe new physics. [...]