Report: Bad Honnef Physics School on Searching Quantum Gravity in the Sky
In the 3rd week of February of 2025, the German Physical Society (DPG) Bad Honnef Physics school on Searching quantum gravity in the sky was organized at the Physikzentrum in Bad Honnef under the BridgeQG COST action. The 5-day long school, that was attended by roughly 70 masters and PhD students from all over the world, included experimental as well as theoretical lectures on quantum gravity phenomenology, with the central subject being Lorentz invariance violation (LIV) and its experimental observations in high-energy astrophysics.
The school was kickstarted by an introductory talk by Christian Pfeiffer(ZARM), one of the main organisers of the school together with Giulia Gubitosi (U Napoli), Tomislav Terzić (U Rijeka) and Jose Manuel Carmona (U Zaragoza). The theoretical lecture was given by Giacomo Rosati wherein he touched upon two phenomenological approaches that aim at modifying special relativity, viz., LIV and doubly special relativity (DSR). The experimental lectures covered the different aspects and complexities involved in observing potential LIV through astrophysical sources. These were given by Jelena Striškovič, Rafael Alves Batista and Caterina Trimarelli wherein the hunt for LIV observations via time-delays in high-energy gamma-ray photons and via interaction threshold reactions, as well as the experimental challenges in the detection of cosmic messengers, were discussed in detail.
Apart from these main topics of the school, there were two additional talks covering potential deviations between theory and observations. The first of these was given by Jackson Levi Said wherein the current tensions in cosmological observations were discussed. The second of the these, which concluded the school was given by Flaminia Giacomini wherein she discussed theoretical notions in low-energy quantum gravity and introduced some thought-experiments aiming at identifying quantum gravity effects.
During the school, all attendees had the opportunity to visit the Effelsberg 100-m Radio Telescope, gaining hands-on experience with one of the world’s largest fully steerable radio telescopes. Participants learned about its working principles and operational procedures, adding a practical dimension to their understanding of observational techniques relevant to quantum gravity phenomenology.
The Bad Honnef Physics Center, with its castle-like architecture, comfortable accommodations, and excellent dining facilities, provided an ideal setting for immersive learning. The residential format encouraged continuous scientific exchange among students and lecturers, strengthening the sense of community in the field. There were also numerous social activities, including shared meals, a poster session, and a karaoke night, which further fostered interactions among participants. The school was co-funded by the BridgeQG COST action, which aims to bridge the gap between low- and high-energy quantum gravity research initiatives and foster further interaction. In alignment with this objective, the next edition of the school is planned for 2026, with a focus on low-energy quantum gravity.
Paul Hartung, Roman Kemper, Jonas Neuser, Niklas Rodenbücher and Ashay Sathe (Institute for Quantum Gravity, FAU Erlangen)