Theorie Palaver

I will discuss the real-time dynamics of metric perturbations around the AdS black hole and argue that the dynamic of these modes is captured by a set of designer scalars in the background geometry. Using these results I will obtain the real-time Gaussian effective action, which includes both the retarded response and the associated stochastic fluctuations. Finally, I will discuss extensions beyond linear response.

Cosmological first-order phase transitions are said to be strongly supercooled when the nucleation temperature is much smaller than the critical temperature. The phase transition takes place slowly and the probability distribution of bubble nucleation times is maximally spread. Hubble patches which get percolated later than the average are hotter than the background after reheating and potentially collapse into primordial black holes (PBHs). I will give a review of this PBHs formation mechanism and of its most recent developments.

In the last decade, several measurements have been hinting at the possibility of Beyond Standard Model physics in B decays. Some of these observables have stayed “anomalous” after several experiments released multiple measurements of such quantities, while others have recently suffered a different fate. In this seminar I will recap the current status of experimental anomalies, critically reviewing the theoretical description of these observables in the Standard Model. I will therefore identify which are the quantities with the highest probability of being affected by New Physics, and which are the ones that on the other hand do not require an extension of the SM any longer.

The state-of-the-art in current two-loop QCD amplitude calculations is at five-particle scattering. In contrast, very little is known at present about two-loop six-particle scattering processes. In recent years, the results for one-loop hexagon integrals to higher order in the dimensional regulator become available as well as the results on the maximal cut of the planar two-loop six-point integral families. In this talk, I will show the progress made in computing planar two-loop six-particle Feynman integrals beyond the maximal cut using the differential equations method. In particular, I will discuss the canonical basis for several integral families in four space-time dimensions and their function space.

In recent years, modular invariance has been applied to the SM flavour puzzle, yielding compelling results. In this string-inspired paradigm, one does not require a multitude of scalar fields (flavons) with aligned VEVs and complicated potentials. Taking a bottom-up approach, one may instead rely on a single complex field -- the modulus. Yukawa couplings and mass matrices are obtained from functions of its VEV, which can be the only source of flavour symmetry breaking and of CP violation. Such predictive modular setups may, among other things, shed light on the patterns of fermion mixing, the origin of fermion mass hierarchies and the strong CP problem.

In this talk, I will go over the role of small instantons (SI) in increasing the axion mass. These SI will also enhance the effect of CP-violating operators which shift the axion potential minimum by an amount proportional to the flavorful couplings of the theory. Since physical observables must be flavor basis independent, we construct a basis of determinant-like flavor invariants that arise in instanton calculations containing the effects of dimension-six CP-odd operators. This new basis provides a more reliable estimate of the shift of the minimum of the axion potential, which is severely constrained by neutron electric dipole moment experiments. We show explicitly how these quantities arise in the case of 4-quark and semi-leptonic operators, and how they can be used to constrain the ratio of the scales of SI and CP-violation. More generally, the flavor invariants introduced, together with an instanton NDA, can be used to more accurately estimate small instanton effects in the axion potential arising from any effective operator. We will also discuss how other shift-breaking effects can be enhanced in the presence of SI.

Finding interpretable order parameters for the detection of topological dynamics and critical phenomena can be a challenging endeavour in lattice field theories. Tailored to detect and quantify topological structures in noisy data, topological data analysis (TDA) allows for the construction of sensitive observables. In this talk I will discuss two research projects, which highlight the potential of TDA for lattice field-theoretical studies. The first utilizes TDA to investigate the role of topological defects in regimes governed by universal self-similar dynamics. More specifically, in simulations of the paradigmatic O(N) vector model, the dynamics of topological defects can be studied via Betti curves computed from local energy densities. Based on Monte Carlo simulations of SU(2) lattice gauge theory, the second project shows how TDA computed from chromoelectric and -magnetic fields, topological densities and Polyakov loops can be used to uncover a multifaceted picture of the deconfinement phase transition. This application-oriented talk is based on joint work with Viktoria Noel, Jan Pawlowski and Julian Urban.

Parton showers are essential tools for interpreting particle-collision data. To get the most out of available and upcoming data, it is important that these showers incorporate state-of-the-art theoretical predictions. The PanScales project aims to design parton showers that achieve higher logarithmic accuracy than any of the standard tools used at present. This talk will discuss the construction of logarithmically accurate parton showers, including the recent achievement of next-to-next-to-leading-logarithmic accuracy for the wide class of e+e- observables known as event shapes, and its impact on phenomenology.

Future electron-positron colliders, such as the CEPC, FCCee, and ILC, are poised to explore a new precision frontier, enabling an unprecedented level of scrutiny of the electroweak (EW) sector of the Standard Model (SM) and potentially uncovering new physics beyond the SM. Achieving this requires a deeper understanding of the SM through the calculation of radiative corrections to various well-defined observables, specifically the electroweak precision observables (EWPOs). The first part of the talk provides a brief review of the EWPOs and the forefront of precision studies of these observables at future electron-positron colliders. In the second part, we introduce a novel modular framework for describing EW scattering and decay processes, including but not limited to Z-resonance physics. This framework maintains gauge invariance while ensuring extensibility. It has been implemented in the publicly available object-oriented C++ library GRIFFIN, featuring full NNLO and leading higher-order contributions on the Z-resonance, as well as NLO corrections off resonance. This framework is also capable of making predictions for new physics models relevant to these processes and can interface with Monte Carlo programs to account for real radiation.

In many extensions of the Standard Model, the universe underwent one or several first order phase transitions. Such phase transitions proceed via the formation and collision of bubbles. The bubble collisions can source a stochastic gravitational wave background signal. In the case of the electroweak phase transition, the characteristic frequency would fall right in the sensitivity band of LISA. We can thus use data from gravitational wave experiments to probe physics beyond the standard model. In this talk, I will discuss the contribution to the gravitational wave signal from sound waves, which is often the dominant contribution. Predictions of the gravitational wave spectrum typically rely on hydrodynamic lattice simulations of the scalar-plasma system. Hydrodynamic solutions of a single expanding bubble provide a bridge between the particle physics model and the hydrodynamic lattice simulation and encode much of the underlying particle physics information. Two relevant quantities in this computation are the bubble expansion velocity and the kinetic energy budget. I will discuss the computation of both quantities and present two approximation schemes for computing the wall velocity: the scenario of local thermal equilibrium and of a large enthalpy jump between the two phases.

High-luminosity colliders and fixed-target facilities using proton beams are sensitive to new weakly coupled degrees of freedom across a broad mass range. In this talk, we will discuss various production modes for dark vector particles in proton beam experiments. First, we will set the stage by reviewing light physics models, including new vector particles, discuss how these models could solve the shortcomings of the SM, and present some current and future search strategies. After briefly discussing dark photon production in meson decays and Drell-Yan, we will have a closer look at dark bremsstrahlung. Dark bremsstrahlung is particularly important for dark vectors with masses between 0.5-1.5 GeV due to resonant mixing with hadronic resonances. This production mode will be crucial for sensitivity predictions for future experiments like SHiP and proposals like the Forward Physics Facility. We revisit the calculation of dark photons via initial state radiation in non-single diffractive scattering, using an improved approach to the splitting function and the timelike electromagnetic form factor.

The fact that neutrinos are massive particles can be neatly explained by the existence of (at least two) additional neutrinos, called sterile neutrinos. Depending on their mass, sterile neutrinos can be looked for in various experiments. I will discuss how sterile neutrinos can be probed indirectly in neutrinoless double beta decay experiments and how this search compares to more direct probes and how it can test low-scale leptogenesis as a solution for the baryon number asymmetry of the universe.