SEMESTER 2025 - SUMMER




04.03.2025

Andreas Trautner

CFTP, IST, University of Lisbon

Electroweak scale hierarchy from conformal and custodial symmetry


I will introduce the idea of "Custodial Naturalness" to explain the origin of the electroweak scale hierarchy. Custodial Naturalness is based on classical scale invariance as well as an extension of the Standard Model (SM) scalar sector custodial symmetry to SO(6). This requires a single new complex scalar field charged under a new U(1)​ gauge symmetry which partially overlaps with B-L. Classical scale invariance and the high-scale scalar sector custodial symmetry are radiatively broken by quantum effects that generate a new intermediate scale by dimensional transmutation. The little hierarchy problem is solved because the Higgs boson arises as pseudo-Nambu-Goldstone boson of the spontaneously broken SO(6) custodial symmetry. The minimal realization of Custodial Naturalness has the same number of parameters as the SM and predicts testable new physics in the form of a heavy Z' as well as a light but close-to invisible dilaton. Simple extensions furthermore allow to explain neutrino masses and Dark Matter - only in a region of parameter space that can be completely excluded by future colliders.

Slides


18.03.2025

Kodai Sakurai

Tohoku University

Primordial black hole formation by inverted bubble collapse


A primordial black hole (PBH) is one of the promising candidates for dark matter. PBHs can form when significant density perturbations are generated in the early Universe. Various mechanisms for producing overdense regions that lead to PBH formation have been proposed in the literature. Many of these mechanisms postulate that such an overdense region has spherical symmetry; however, in general, deviations from a perfect sphere can occur, making PBH formation nontrivial. In this talk, we discuss a novel mechanism for PBH formation in which the generated overdense region maintains spherical symmetry. We also demonstrate that the observed microlensing events in the OGLE and Subaru HSC data can be explained by applying this new mechanism to extended Higgs models.

Slides


01.04.2025

Werner Porod

Univeristy of Würzburg

Using gauge/gravity duality for strongly interacting models


We use a holographic model of chiral symmetry breaking based on gauge/gravity duality to determine the meson and baryon spectrum of strongly interacting models. We introduce this approach by applying it first to two flavour QCD and then include also flavour effects like different quark masses for three flavour QCD. Moving to Composite Higgs models, we use this approach for different models with varying number of colors and flavours. We will focus in particular on models where we can compare part of our results to related lattice studies.

Slides


15.04.2025

Ayuki Kamada

University of Warsaw

Quantum theory of dark matter scattering


A long-range force between dark matter particles makes significant impacts on dark matter phenomenology. It enhances the annihilation cross section at the late Universe (Sommerfeld enhancement), which affects the prospects for detecting annihilation products (indirect detection experiments). It also leads to a large self-scattering cross section, which forms a significant core in dark matter halos. When the Sommerfeld enhancement factor is significantly large for a certain value of the parameter (resonance), the self-scattering cross section is also resonantly enhanced. In this talk, we first review how the Sommerfeld enhancement factor and self-scattering cross section are usually computed in quantum mechanics. Then, we show that partial-wave unitarity of Sommerfeld-enhanced annihilation cross section is violated on resonance. In the end, we discuss the on-going efforts to restore unitarity.

Slides


29.04.2025

Sreemanti Chakraborti

IPPP Durham


Seminar is broadcast online at Zoom

Searching Ultralight Axions with Quantum Technology


In this talk, I will discuss axion-like particles (ALP) as dark matter candidates in the "ultralight mass regime". Starting from the ALP Lagrangian at the UV scale, a consistent QFT treatment is required to obtain interactions at low energy. A plethora of quantum sensor experiments has been designed so far to search for very light ALPs that are particularly sensitive to these effects because they probe large values of the decay constant for which running effects become important. In addition, while linear axion interactions are set by its pseudoscalar nature, quadratic interactions are indistinguishable from scalar interactions. This makes the two types of interactions sensitive to different categories of experiments. I will discuss the reach of various experiments exploiting quantum technology via quantum sensors like atomic clocks, optical interferometers, atom interferometers, etc, and microwave cavity-haloscopes. Lastly, I will touch on the nonlinear behaviour of the ALP field close to the surface of the earth and identify the experiments impacted by this effect.


13.05.2025

Stefan Lederer

Technische Universität München



27.05.2025

Aditya Batra

CFTP, University of Lisbon



10.06.2025

Dominik Stöckinger

TU Dresden