Timescape versus Lambda CDM supernovae evidence for foundational change
Institut für Theoretische Physik, Online; Note unusual time
The timescape cosmology returns to first principles, with quasilocal gravitational energy replacing dark energy, to explain apparent cosmic acceleration. As inhomogeneities grow, they back react on average cosmic expansion, which differs from conventional FLRW models. Crucially, dynamical spatial curvature arises as time-varying gradients of the kinetic energy of expansion, and depends directly on the void volume fraction. The timescape expansion history is close to Lambda CDM , but with differences at a precision which we are now finally probing. Whereas Lambda CDM is increasingly challenged, independent observational tests now favour timescape. I will present a recent analysis of the Pantheon+ type Ia supernovae data set by Bayesian methods. When considering the entire Pantheon+ sample, we find very strong evidence (ln B > 5) in favour of timescape over Lambda CDM . Furthermore, even restricting the sample to redshifts beyond any conventional scale of statistical homogeneity, z > 0.075, timescape is preferred over Lambda CDM with ln B > 1. The relation of our results to those of other surveys (DES, DESI etc) that find increasing tensions for Lambda CDM, will be discussed. In particular, the recent DESI evidence for Âevolving dark energy is consistent with timescape's non-FLRW evolution, as predicted in 2009. References: [1] A. Seifert, Z.G. Lane, M. Galoppo, R. Ridden-Harper, D.L. Wiltshire, ÂSupernovae evidence for foundational change to cosmological modelsÂ, MNRAS Letters 537 (2025) L55-L60; [2] Z.G. Lane, A. Seifert, M. Galoppo, R. Ridden-Harper, D.L. Wiltshire, ÂCosmological foundations revisited with Pantheon+Â, MNRAS 536 (2025) 1752-1777.
16:30
Heidelberg Joint Astronomical Colloquium
Nicole Reindl
Unlocking the various evolutionary pathways of sun-like stars
There is no one way to live a life. How true this statement is also for stars is well reflected in the zoo of H-deficient stars, and strikingly beautiful and diverse planetary nebulae morphologies. In this talk, I will explore how late thermal pulses, stellar mergers, Type Ia supernovae, and magnetic fields can dramatically alter the observable characteristics of evolved stars. Understanding these processes helps us piece together the various evolutionary pathways that sun-like stars can follow.
17:00
Particle Colloquium
Dr. Kai Schweda
The ALICE-3 upgrade plans
Physikalisches Institut INF 226, Konferenzraum 1-3 (Room 00.101 bis 00.103)
Wednesday, 2 July 2025
09:30
Seminar Dynamik und Struktur von Atomen und Molekülen
Deepthy Mootheril; Ultra-cold dynamics and collisions
Ultrafast Relaxation Pathways in Hydrogen-Bonded and Aromatic Clusters
Zentraler Seminarraum / Central seminar room (library)
14:15
Kosmologie und Elementarteilchenphysik
Laura Herold
Cosmological neutrino mass bounds with DESI from a Bayesian & frequentist perspective
Institut für Theoretische Physik, Online, Note unusual date (Tunch schedule)
The DESI galaxy survey has recently placed the tightest constraint on the sum of neutrino masses to date. For such effects Âbelow the detection limitÂ, where data can only infer upper bounds, Bayesian and frequentist methods can give important complimentary information. I will begin with an overview of the frequentist profile likelihood method, its advantages and limitations. Using a frequentist and Bayesian toolbox, I will discuss neutrino mass constraints from Planck and DESI data. In particular, I will focus on the impact of different assumptions about the neutrino mass hierarchy on the inferred mass bounds: while it has been shown for previous experiments that the normal and inverted neutrino mass hierarchies are well approximated by three degenerate-mass neutrinos, we scrutinise this approximation in light of recent DESI data.
Thursday, 3 July 2025
11:15
Kaffeepalaver
Chloe Goupy
Probing sub-eV neutrino mass and light sterile neutrinos with the KATRIN experiment
Central seminar room, library building
The absolute mass scale of the neutrino remains one of the key open questions in particle physics and cosmology. The Karlsruhe Tritium Neutrino (KATRIN) experiment addresses this challenge by precisely measuring the energy spectrum of electrons from tritium beta decay near its endpoint. KATRIN combines a high-intensity gaseous molecular tritium source with a high-resolution electrostatic spectrometer with magnetic adiabatic collimation. This approach has enabled KATRIN to reach sub-eV sensitivity and set a world-leading upper limit of 0.45 eV/c^2 (90 % confidence level) on the effective electron anti-neutrino mass, based on data from the first five measurement campaigns. These results reflect major advancements in background suppression, control of systematic uncertainties, and statistical precision.
In this talk, I will present the latest results from KATRIN, including the neutrino mass analysis as well as recent results on probing the eV-scale sterile neutrinos parameter space using the same experimental data.
ARI Institute Colloquium
Nicolas Moens
The future of massive star atmosphere models: Multi-D RHD
ARI, Moenchhofstrasse 12-14, Seminarraum 1.OG
Massive stars drive galactic chemical evolution and are precursors to compact objects and gravitational wave sources. Our understanding of massive stars relies on matching observations to detailed synthetic observables computed using methods that model the star's atmosphere and winds. Traditionally, most modeling efforts of hot massive stars presume 1D spherically symmetric, steady-state atmospheres. These simplifications allow for more computational resources to be spent on accurate NLTE radiative transfer calculations. However, newer models suggest that these simplifications are not sufficiently accurate for stars at the higher end of the mass scale. In reality, multi-dimensional effects create turbulent regions with complex density and velocity structures within both the atmosphere and wind of the star. Our new method simplifies the complex NLTE radiative transfer but incorporates these multi-dimensional, time-dependent dynamics. This approach allows us to capture complex behaviors that have implications for the general atmospheric and wind structure. Applying our method has yielded several successful results. After explaining our methodology, in this talk I will highlight how multi-D models explain the winds of WR stars and predict macro-turbulent broadening of O-stars.
16:15
Teilchen-Tee
Timothy Linden
Celestial Bodies as Dark Matter Detectors
Institut für Theoretische Physik, Phil12, SR106
Terrestrial direct detection experiments have placed very strong constraints on any potential scattering cross-section between dark matter particles and standard model particles. However, the final sensitivity of these detectors are limited both by economic considerations, as well as the relatively narrow theory-target reach of such experiments -- which is focused on GeV-scale spin-independent dark matter/baryon scattering. The large mass of celestial bodies (e.g., planets, stars and compact objects) offer new possibilities to probe rare dark matter interactions. In this talk, I will discuss several exciting studies which show the potential for celestial bodies to provide leading constraints on the direct detection parameter space which are highly complementary to terrestrial experiments.
Friday, 4 July 2025
17:00
Physikalisches Kolloquium
Prof. Dr. Ullrich Köthe
Generative Neural Networks for the Sciences
KIP, INF 227, Hörsaal 1
Generative modelling with normalizing flows has worked well in scientific applications like simulation-based inference. However, the peculiar design makes it difficult to incorporate prior knowledge (such as laws of physics or chemistry) into their architecture. Free-form flows eliminate this restriction by means of a new training algorithm. Manifold free-form flows elegantly exploit these opportunities in the case when we know that the data reside on a manifold. The talk will explain the underlying theory and present experimental evidence for the promising behavior of the new approach.
Tuesday, 8 July 2025
11:15
Seminar Theoretische Quantendynamik
Dr. Sergey Volkov, MPIK
Two-loop vacuum polarization in the Coulomb field of a nucleus
Seminar room 242, Bothe Lab
14:15
Kosmologie und Elementarteilchenphysik
Carlos Pastor Marcos
TBA
Institut für Theoretische Physik, Phil19
TBA
16:30
Heidelberg Joint Astronomical Colloquium
Stephen Smartt
Compact star mergers, kilonovae and r-process element production
To arrange a visit with the speaker during the visit, please contact their host: Fabian Schneider
17:00
Particle Colloquium
Prof. Dr. Pamela Ferrari
Highlights of the HL-LHC physics projections by ATLAS and CMS
Physikalisches Institut INF 226, Konferenzraum 1-3 (Room 00.101 bis 00.103)
Wednesday, 9 July 2025
09:30
Seminar Dynamik und Struktur von Atomen und Molekülen
NN
tba
Zentraler Seminarraum / Central seminar room (library)
16:30
Zentrum für Quantendynamik Kolloquium
Prof. Sylvain Nascimbene
Exploring quantum Hall physics with ultracold dysprosium atoms\n
Physikalisches Institut, INF 226, K 1-3
Exploring quantum Hall physics with ultracold dysprosium atoms Prof. Sylvain Nascimbène Laboratoire Kastler Brossel, Collège de France, Paris Ultracold atomic gases offer a versatile platform for exploring rich phenomena in quantum matter. In particular, topological states akin to those found in the quantum Hall effect can be engineered by simulating orbital magnetic fieldsÂan approach greatly facilitated by the use of synthetic dimensions. In this talk, I will present our experimental realization of a quantum Hall system using ultracold gases of dysprosium atoms. By leveraging the atomÂs large internal spin (J=8), we encode a synthetic dimension and couple it to atomic motion via two-photon optical transitions, which generates an effective magnetic field. We observe hallmark signatures of quantum Hall physics, including a quantized Hall response and gapless, chiral edge modes. I will then describe a more intricate experiment designed to probe spatial entanglement by simulating the so-called entanglement Hamiltonian. Using the Bisognano-Wichmann theoremÂwhich relates the entanglement Hamiltonian to a spatially deformed version of the original systemÂwe implement this deformation along the synthetic dimension. Lastly, I will discuss our recent investigation into a topological phase transition, induced by introducing an additional lattice potential. I will highlight the systemÂs behavior in the critical regime and explore the emergent features associated with the transition.
Thursday, 10 July 2025
11:00
Teekolloquium
Professor Ulrich Uwer, Professor Vincenzo Vagnoni
Precision Physics at a Hadron Collider: Highlights from the LHCb-Experiment
Grosser Hoersaal/Big Lecture Hall (library)
Since the start of the Large Hadron Collider (LHC) the LHCb experiment
has become the leading flavour physics experiment worldwide. Initially
designed to probe the matter-antimatter asymmetry of the universe by
precision measurements of CP violation in heavy flavour decays, it
continuously expanded its physics portfolio to cover also QCD and
electroweak physics, the study of heavy ion collisions and most recently
also fixed target physics. The kolloquium will start with a presentation
of highlights from flavour- and electroweak physics, the second part
will focus on strong interactions and new exotic states found by
the experiment.
11:15
ARI Institute Colloquium
Kai Wu
From Debris Disks to Million-Body Clusters: Planetary Perturbations, Stellar Interactions, and DRAGON-III's First Insights
ARI, Moenchhofstrasse 12-14, Seminarraum 1.OG
This talk has two topics. The first part is about planetary systems in star clusters. Several tens of planetary systems, including our Solar System, contain both planets and debris structures. Most stars are believed to be born in clustered environments, such as in star clusters. In such environments, debris discs evolve through interactions with stellar neighbours and planets. I use gravitational N-body simulations to investigate how the joint effect of star cluster environments and planets affects the dynamical evolution and stability of debris discs. I focus on how (i) the presence of a planet, (ii) the density of the star cluster, and (iii) the orbit of host stars within the cluster affect the stability and evolution of debris discs, as well as the characteristics of escaping particles and remaining discs. The second part of my talk is about globular clusters. They are abundant in galactic disks and spheroids, serve as ideal laboratories for studying stellar evolution alongside Newtonian and relativistic dynamics. The previous study of Dragon-II (Arca Sedda et al. 2023) successfully revealed astrophysical details of these dynamical systems, including gravitational wave signals from compact object mergers that would be measured by LIGO/Virgo/KAGRA. As a continuation of DRAGON-II, I present the DRAGON-III project and report on its preliminary results, which focuses on the simulations of million-body globular clusters and million-body nuclear clusters over 10 Gyr.
Friday, 11 July 2025
17:00
Physikalisches Kolloquium
Prof. Dr. Stefan Filipp
Advancing Quantum Information Processing with Superconducting Circuits
KIP, INF 227, Hörsaal 1
Quantum computers have the potential to solve complex problems efficiently. However, to unleash their full potential, complex quantum systems have to be manufactured, manipulated and measured with unprecedented accuracy and precision. In this presentation I will focus on superconducting qubits as one of the most promising platforms for quantum computing. I will illustrate the building blocks of a quantum processor using a system based on 17 transmon-type qubits, which we are currently operating in our laboratory. In this architecture tunable coupling elements are harnessed to generate multi-qubit operations between two or more qubits and to efficiently create many-body entanglement. Moreover, I will address alternative superconducting qubits with improved protection against environmental influences.
