Organizers: Almudena Arcones, Jens Braun, Michael Buballa, Hans-Werner Hammer, Kai Hebeler, Gabriel Martínez-Pinedo, Daniel Mohler, Guy Moore, Robert Roth, Achim Schwenk, Jochen Wambach
Time: Tuesdays, 13:30 o'clock (new time!)
Place: S2|11, Room 10
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25.06.2026 13:30 S2|14, IKP Lecture Hall |
Prof. Gail McLaughlin (NC State University, USA) r-process element synthesis: neutrinos, neutron capture, and gamma rays Although heavy elements like gold and platinum are known to form through the rapid neutron capture process (r-process), their exact cosmic origins remain uncertain. Neutron star mergers account for some r-process production, but a substantial second component may come from other environments, such as magnetorotational supernovae. I will discuss a few key open questions surrounding the r-process, including the influence of neutrínos, neutron capture physics, and observational prospects with gamma-ray satellites |
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18.06.2026 13:30 S2|11 10 |
Dr. Smaranika Banerjee (TU Darmstadt) The cosmic treasure hunt: how does the universe make the elements like gold We are made of, and surrounded by, elements such as oxygen, carbon, iron, and even gold, yet the question of where the heaviest elements, such as gold, come from remains one of the great mysteries in astrophysics. A leading theoretical hypothesis is that these heavy elements are produced in binary neutron star mergers. When two neutron stars collide, they eject neutron-rich matter in which heavy elements are formed through rapid neutron-capture nucleosynthesis, or the r-process. The radioactive decay of these newly synthesized elements powers a short-lived ultraviolet, optical, and infrared transient known as a kilonova, which can be observed with telescopes. At the same time, the merger produces gravitational waves detectable by ground based observatories, making these systems powerful multi-messenger sources. The first joint detection of gravitational waves and a kilonova in 2017 confirmed neutron star mergers as sites of heavy-element production, but important questions remain: do they produce enough material to explain the heavy elements we observe, what can kilonova light curves and spectra reveal about the ejecta, and are additional cosmic sources needed? In this talk, I will introduce the broader context and importance of this field, discuss these open questions, and highlight recent progress in understanding kilonovae and neutron star mergers. |
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27.05.2026 ! 11:00 ! S2|11 10 |
Prof. Charlotte Elster (Ohio University, Athens OH) Ab Initio Folding Optical Potentials for Proton-Nucleus Scattering based on NCSM and SA-NCSM One-Body Densities The calculation and derivation of microscopic optical potentials for calculating scattering observables for elastic scattering from spin-zero nuclei has a long tradition. So-called microscopic `full-folding' models based on a nuclear density matrix and a fully-off-shell two nucleon t-matrix have been developed mainly for closed shell nuclei heavier than Oxygen-16 in the 1990s. With the advent of ab initio structure calculations in the No-Core-Shell Model (NCSM) for light nuclei, and the symmetry-adapted (SA) NCSM for heavier nuclei, nonlocal as well as translationally invariant one-body densities can be constructed and employed in calculations of effective interactions in proton-nucleus scattering. This talk will explain the approach based on the spectator expansion to proton-nucleus scattering and show how the first order term can be obtained consistently based on a given chiral nucleon-nucleon interaction. Results for proton and neutron scattering from 6He to 40Ca in the energy regime between 65 and 200 MeV laboratory projectile energy will be shown with emphasis on recent work of proton and neutron scattering from 24Mg to 32Mg, where we show that ab initio calculations may give guidance to extrapolations of phenomenological optical potentials away from the valley of stability. I will also discuss some current work based on SVD decomposition of off-shell NCSM one-body density matrices and leading order optical potentials derived from them. |
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21.05.2026 13:30 S2|11 10 |
Prof. Dr. Nathan Harshman (American University, Washington, DC) The Golden Age of One-Dimensional Anyons: Theory and Experiment All fundamental particles obey bosonic or fermion statistics, but for effective theories in low dimensional systems, topological quantization provides a non standard possibility: anyons. Anyons in two-dimensional systems are theoretically well-understood and quasiparticles with anyons obeying fractional statistics have been directly measured. A proliferation of theoretical models has sought to replicate anyons with fractional statistics in one-dimensional systems, and recent experimental advances with ultracold atoms in one-dimensional optical traps have implemented some of these models. What can we learn about indistinguishability, topological interactions, and topological quantum computation from these models? And wait … are anyons even possible in one dimension? In this talk, I will motivate the search for anyons in one dimension, explain the three interaction mechanisms that generate one-dimensional anyons, and comment on recent experimental implementations. |
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12.02.2026 13:30 S2|11 10 |
Prof. Mark Alford (Washington University, St. Louis) Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the “Urca process”) is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation. |
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26.01.2026 16:15 S1|03 283 Wilhelm-Köhler-Saal |
Jun.-Prof. Lena Funcke (Universität Bonn) Towards Solving Computational Challenges in Lattice Field Theory: From Deep Learning to Quantum Computing In lattice field theory, several parameter regimes remain inaccessible to conventional Monte Carlo methods, including topological terms, non-zero baryon density, and real-time dynamics. Using lower-dimensional benchmark models as examples, I will review new approaches to overcoming these challenges, based on deep learning, tensor networks, and quantum computing. Finally, I will discuss the requirements for integrating these methods into (3+1)-dimensional lattice simulations in the future, with a focus on Lattice QCD. |
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15.01.2026 13:30 S2|11 10 |
Dr. Maxim Mai (Universität Bern) A strange-ness loop: QCD to EFT to dynamically generated resonances and back to (lattice) QCD The study of strongly interacting particles (hadrons) is a field that remains riddled with many unanswered questions. One of the most fundamental is the form of the excited states spectrum. Additionally, the reasons behind the varying complexities and the nature of some individual states also remain elusive. To address these questions several powerful tools have been developed, including Lattice QCD, Chiral Perturbation theory, and S-Matrix techniques. In my talk I will review recent progress in combining these techniques. Specifically, I will focus on the bridge between Lattice QCD based and traditional hadron spectroscopy through models based on Effective Field Theories and S-Matrix theory. The showcased examples will range from the elusive Lambda(1405) to recently re-discovered three-body resonance omega(782) and pi(1300). |
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18.12.2025 13:30 S2|11 10 |
Dr. Takami Kuroda (Max Planck Institute for Gravitational Physics (Albert Einstein Institute)) Accretion induced collapse of white dwarfs and multi-messenger signals The nature of lower ejecta mass in accretion- or merger-induced collapse (AIC/MIC) of white dwarfs (WDs) could be the key to understanding rapidly evolving transients, whose features are hardly interpreted by standard supernovae (SNe). WDs in a binary system may acquire mass from its non-degenerate companion star or through a merger with its companion WD. Depending on the mass accretion history, WDs can avoid a violent nuclear burning, i.e., Type Ia SNe, and steadily increases both their mass and central density, resulting in electron capture SN (ECSN). Aiming at discussing such ECSN dynamics and associate multi-messenger signals, we conducted numerical relativity simulations for the collapse of rotating magnetized white dwarfs (WDs) in three dimension. We observed prompt-like explosions dominated by a bipolar structure and the emergence of strong spiral waves in rapidly rotating models, which can efficiently eject neutron rich material. In this talk I will present more detailed explosion dynamics and their potential observed features aiming at some of the rapidly evolving optical transients, such as fast blue optical transients (FBOTs). |
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27.11.2025 13:30 S2|11 10 |
Evan O’Connor (Stockholm University) 3D Core Collapse simulations spanning compactness I will present recent 3D core-collapse supernova and multimessenger work from the Stockholm Supernova theory group. These simulations include: (a) magnetohydrodynamic simulations of a high compact progenitor, touching upon the explosion mechanism of rapidly rotating, magnetized core collapse events and particularly on the impact of rotation and magnetic fields; (b) the core-collapse, and long term evolution of a low-metallicity, low-mass, commonly-explored progenitor allowing a comparison among simulation groups; and (c) a preliminary look at a larger set of simulations spanning progenitor mass using a more approximate neutrino treatment and (d) a sneak peak at several cases of precollapse, multidimensional evolution in 3D. Collectively these simulations span a broad range of the progenitor population and highlight the growing diversity of outcomes from core collapse, including neutron stars, magnetars, as well as simultaneous explosions and black hole formation. |
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25.11.2025! 10:00! S2|11 10 |
Dr. Lucca Boccioli (University of California, Berkeley) Explodability matters: how realistic neutrino-driven explosions change explosive nucleosynthesis and remnant masses When a core-collapse supernova explodes, it ejects elements synthesized during the post-main-sequence evolution of the star, and it produces new elements during the explosion (the so-called explosion nucleosynthesis). In the aftermath of the explosion, a neutron star is left behind. How massive the leftover neutron star is, and how much mass of each element is ejected during the explosion are two of the questions I will address during this talk. The neutron star mass distribution impacts the remnant population of the galaxy, and therefore is a key input for population synthesis studies (for example, it makes up the seeds for neutron star merger events). The ejected elements contribute to enriching the interstellar medium, which is used to form the next generation of stars, and can therefore be observed in their photosphere. One of the biggest uncertainties in predicting both remnant masses and nucleosynthetic yields is the explodability, i.e., which stars explode? Which ones do not and, instead, end up as failed supernovae, forming a black hole? Only state-of-the-art models of the explosion can answer this question. In this talk, I will present recent results using 1D simulations that include sophisticated neutrino transport, general relativistic effects, and a mixing-length theory model for neutrino-driven convection, which, as I will show, is a key aspect in the explosion. |
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19.11.2025! 12:00! S2|11 10 |
Dr. Somdutta Ghosh (University of New Hampshire, Durham, USA) Neutrino flavor oscillation in neutron star mergers Neutrino flavor oscillations are ubiquitous in neutron star mergers, affecting the merger dynamics and the electron fraction of the ejecta, which will subsequently impact the r-process nucleosynthesis and heavy-element abundances. Over the years, numerous studies have explored neutrino physics in dense environments such as those found in neutron star mergers. These studies suggest that flavor oscillation due to instabilities can be significant close to the central compact object. To account for these flavor instabilities, merger simulations need to solve the neutrino quantum kinetic equations. However, solving the quantum kinetic equation directly in a merger simulation is far from feasible, even with the available high-performance computational resources. In this talk, I will present our efforts to incorporate flavor instabilities, particularly fast flavor instabilities, in mergers using sub-grid modeling. I will present a machine-learning model and an analytical mixing scheme that can predict the outcome of fast flavor oscillation on post-merger snapshots and compare their performance. I will also discuss the challenges of incorporating these models into the available neutrino transport scheme. |
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06.11.2025 13:30 S2|11 10 |
Prof. Jonathan Engel (University of North Carolina) CP Violation and Nuclear Schiff Moments: Ab Initio and DFT After discussing the search for CP violation beyond the Standard Model through atomic and molecular dipole moments, I review the argument that for CP violation coming from the nucleus, the quantity that usually induces these dipole moments is the Schiff moment. I then review existing calculations of Schiff moments in several important nuclei and discuss work in progress in ab initio schemes to improve the accuracy of the calculations. |
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30.10.2025 13:30 S2|11 10 |
Nanae Domoto (Research Center for the Early Universe, The University of Tokyo) Signatures of heavy elements in optical and near-infrared spectra Binary neutron star (NS) mergers are promising sites for the rapid neutron capture nucleosynthesis (r-process). The radioactive decay of synthesized elements powers electromagnetic emission called a kilonova. The detection of gravitational waves from an NS merger GW170817 and the observations of the associated kilonova AT2017gfo have provided us with evidence that r-process occurs in the NS merger. However, the abundance pattern synthesized in this event, which is important to reveal the origin of the r-process elements, is not yet fully understood. In the talk, I will present our recent results for identification of elements in the kilonva spectra a few days after the merger. We found that only several elements are important for absorption features, Sr, La, Ce, Gd, and Th, and some of them can explain the observed features in the spectra. We also confirmed our results of identification by utilizing stellar spectra. The direct identification of elements allows us to constrain amounts of synthesized elements. |
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11.09.2025 13:30 S2|11 10 |
Bhabani Sankar Tripathy (Institute of Mathematical Sciences, Chennai/India) Study of doubly bottom and bottom-strange tetra-quark from lattice QCD We present a lattice QCD investigation of isoscalar tetraquark systems involving bottom quarks with explicit flavor content $bb\bar{u}\bar{d}$ and $bs\bar{u}\bar{d}$. In the doubly bottom sector, the study focuses on axialvector $J^P=1^+$ quantum numbers, whereas in the $bs\bar{u}\bar{d}$ channel both axial vector $J^P=1^+$ and scalar $J^P=0^+$ quantum numbers are investigated in search of signatures for possible tetraquark bound states. The calculations are performed on four ensembles with dynamical quark fields up to the charm quark generated by the MILC Collaboration, with lattice spacings ranging from approximately 0.058 fm to 0.12 fm, and at different values of the valence light quark mass $m_{u/d}$, corresponding to pseudoscalar meson masses, $M_{ps}=0.5$, 0.6 and 0.7 GeV. The energy eigenvalues in the finite volume are determined by applying a variational procedure to correlation matrices constructed from two-meson interpolating operators and diquark-antidiquark operators. Continuum extrapolated elastic $S$-wave scattering amplitudes of $BB^*$, $KB^*$ and $KB$ are extracted from the ground state eigenenergies following a finite-volume analysis a' la Leuscher. The chiral and continuum extrapolated binding energy estimates for the isoscalar axial vector doubly bottom tetraquark $T_{bb}$ from the extracted elastic $BB^*$ $S$-wave scattering amplitudes is found to be $\Delta E_{T_{bb}}(1^+)=-116(^{+30}_{-36})$ MeV. In the $bs\bar{u}\bar{d}$, no statistically significant deviations were observed in the ground state energies from the respective elastic threshold energies, leading to no conclusive evidence for any bound states. |
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28.08.2025 13:30 S2|11 10 |
Dr. Rob Pisarski (Brookhaven National Laboratory) Moaty dileptons At nonzero temperature and chemical potential, it is expected that a “moat” regime arises in a large region in T and mu. In such a regime, the energy of the pion has a minimum at nonzero spatial momentum. Such a region may arise experimentally in STAR at low energies, and at CBM at FAIR. I discuss two signals of a moat regime: non-monotonic behavior in Hanbury Brown-Twiss radii (or correlation functions), and new thresholds in dilepton spectra. |
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24.07.2025 13:30 S2|11 10 |
Prof. Bhupal Dev (Washington University in St. Louis) Neutrino Tridents Neutrino tridents are rare Standard Model (SM) processes involving the creation of a charged-lepton pair via an energetic neutrino scattering with a nucleus. These processes provide a precision test of the SM weak sector, and can also serve as a sensitive probe of beyond-the-SM physics. We will present a detailed study of the SM neutrino tridents, including (i) a full 2→4 analytic calculation of the cross section, (ii) both coherent and incoherent scatterings, and (iii) the nuclear modeling uncertainties, in a systematic way. Finally, we comment on the detection prospects of trident events at future accelerator neutrino facilities, such as DUNE. |
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30.06.2025 10:30 (!) S2|11 10 |
Prof. Agnieszka Sorensen (Michigan State University) Searching for the QCD Critical Point with Heavy-Ion Collisions Uncovering the phase diagram of quantum chromodynamics (QCD) is at the heart of numerous theoretical, experimental, and observational efforts worldwide. Prominent efforts include studies aiming to identify the location of the QCD critical point (CP) or understand the apparent peak in the speed of sound in high-density nuclear matter. In pursuing these goals, relativistic collisions of heavy nuclei provide unique opportunitiesto probe hot and dense systems and to study the QCD equation of state (EOS). Recent and upcoming results from the Beam Energy Scan at the Relativistic Heavy Ion Collider (RHIC), given its extraordinary range of available collision energies which can probe systems with vastly different properties, are especially promising. Interpretation of the experimental observables across the RHIC energy range, necessary for uncovering theQCD phase diagram, has been an inspiring challenge for both experiment and theory. In this talk, I will summarize recent advancements in using experimental data and simulations of heavy-ion collisions to put constraints on the QCD EOS and support the search for the QCD CP. |
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26.06.2025 13:30 S2|11 10 |
PhD Stella Schindler New Phases of QCD at finite density In the coming years, the FAIR accelerator will come online at GSI, opening up a new window into the phase structure of QCD. Now is the time to develop a better understanding of what the CBM experiment may find, with particular attention to signals of new physics. Lattice simulations can provide us first-principles information about QCD at zero density, but at nonzero density a sign problem arises from non-Hermiticity of the Dirac operator, obstructing our progress. In this talk, we bring insights from the field of non-Hermitian physics to bear on high energy theory, helping us develop new analytical and numerical tools for QCD phase structure. We show how non-Hermiticity can give rise to a “moat regime” in the vicinity of a critical point. We discuss experimental signatures for these phenomena at FAIR. |
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22.05.2025 13:30 S2|11 10 |
Dr. Yonghui Lin (TU Darmstadt) Phenomenological Study on the Spectroscopy of Charm and Charm-Strange Meson Families In this talk, I will begin with a brief introduction to the fundamental strategies used by both theoretical and experimental communities to identify hadronic states in the context of hadron physics. I will then focus on two recent studies concerning the spectroscopy of charm and charm-strange mesons. The first involves the long-standing puzzle surrounding the nature of the Ds1(2460), one of the earliest observed heavy-flavor mesons exhibiting properties beyond the expectations of the quark model. We demonstrate that its isospin-conserving three-body decay provides a valuable benchmark for probing its internal structure. The second study concerns the identification of the two-pole structure of the D_0^*(2300), incorporating the latest lattice QCD data. Both examples highlight the growing significance of hadronic molecular configurations-bound states driven by one-hadron exchange interactions – as an essential component of hadron spectroscopy, particularly in the heavy quark sector. |
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29.04.2025 (!) 11:00 (!) S2|11 10 |
Prof. Sanjay Reddy (INT, Seattle) Axion condensation in neutron stars The QCD axion was originally proposed nearly five decades ago as a solution to the strong CP problem, providing a dynamical mechanism to explain the preservation of CP symmetry in QCD. In this talk, I will examine the possibility of axion condensation within neutron stars, driven by the extreme baryon densities present in their cores. The analysis employs Chiral Perturbation Theory alongside nuclear interaction models constructed from Chiral Effective Field Theory to evaluate the plausibility of axion condensation under such conditions. Preliminary results suggest that this phenomenon is theoretically well-motivated, though a more refined understanding of nuclear physics at a pion mass near 82 MeV is essential for establishing more definitive conclusions. Should observational or theoretical evidence support—or rule out—the occurrence of axion condensation in neutron stars, it would offer a powerful probe of the axion parameter space. The resulting insights would have profound implications for both axion phenomenology and the microphysical structure of dense nuclear matter within neutron stars. |
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14.04.2025 (!) 10:30 (!) S2|11 10 |
Dr. Jorge Luis Golan Dasilva (Brookhaven National Laboratory) Temperature Dependence of Heavy Quark Diffusion from 2+1-Flavor Lattice QCD We present new lattice results for the heavy quark diffusion coefficient in 2+1 flavor QCD in the temperature range from 163 MeV to 10 GeV. Compared to previous lattice calculations with unphysical light quark masses, we consider near-physical values and a much wider temperature range. Our results for the spatially heavy diffusion coefficient near the crossover temperature are considerably smaller than the estimates obtained by comparing phenomenological models with experimental data and by T-matrix calculations, and are close to the AdS/CFT limit. At high temperatures, however, the spatial heavy diffusion coefficient increases and approaches the NLO weak coupling prediction within the estimated errors. We also find that the dependence of the spatial heavy quark diffusion coefficient on the heavy quark mass on the lattice is weaker compared to the model calculations. Above 10 GeV, lattice calculations lose access to the correlation functions, so in a sense our calculations represent the wilder temperature range that can be reliably extracted with lattice techniques, and also represent the only available results for near-physical light quark masses. |
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03.04.2025 13:30 S2|11 10 |
Prof. Dr. Richard Furnstahl (The Ohio State University) Field theory approach to neural networks Informal Theory Seminar |
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17.02.2025 (!) 14:00 (!) S2|11 10 |
Dr. Alexander Haber (University of Southampton) Weak Interactions in Neutron Star Mergers Weak processes like neutron decay and electron capture play a fundamental role in the transport properties of neutron stars and their mergers. In dense nuclear matter, these processes are called direct and modified Urca processes. In this talk, I will discuss the importance of flavor equilibration via Urca processes in mergers and present a new, more accurate, systematically improvable, and consistent approach to in-medium Urca rates called the “nucleon width approximation”. This novel approach allows us to fundamentally improve the in-medium calculation of weak decays by taking the interactions of the decaying nucleons with the medium consistently into account. |
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13.02.2025 13:30 S2|11 10 |
Dr. Philipp Mösta (University of Amsterdam) Magnetically-powered explosions in the multimessenger era Magnetic fields, turbulence, and jet-driven outflows play a critical role in core-collapse supernovae and compact-object mergers. These transients belong to the most luminous and energetic events observed in the universe and are unique cosmic laboratories probing extreme physics via their multimessenger signals. I will discuss the challenges in both input physics and computational modelling for these systems and highlight recent breakthroughs in full 3D simulations. I will pay particular attention to how these simulations can be used to reveal the engines driving these events and conclude by discussing what remains to be done to maximize what we can learn from current and future time-domain transient surveys. |
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06.02.2025 13:30 S2|11 10 |
Dr. Caroline Robin (Universität Bielefeld and GSI) Complexity, Entanglement and Quantum Simulations of Nuclear Many-Body Systems The development of quantum information has provided new perspectives on quantum many-body problems. In nuclear physics, investigations of concepts such as entanglement and non-stabilizerness (“quantum magic”) can shed further light on the structure of nuclei and underlying forces. At the same time, the language of quantum information is facilitating communication and exchanges of ideas and techniques between fields of physics. Such cross-fertilization, together with the gained insights, are, in turn, enabling the development of improved methods and algorithms for describing nuclear structure and dynamics on classical and quantum computers. I will discuss some recent developments in these areas. |
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30.01.2025 13:30 S2|11 10 |
Dr. Haakon Andresen (Stockholm University) Core-Collapse Supernovae and the Gravitational Waves they emit In this talk, I will summarise the state of core-collapse supernovae research. I will discuss the canonical neutrino-driven machanism and highlight its successes and failures. Where does supernovae research stand today? I will highlight current challanges, focusing on equation-of-state effects. After a broad introduction, I will focus on the gravitational waves emiited by core-collapse supernovae and the information the gravitational radiation conveys regarding the underlying particles, nuclear, and astrophysics. I will round off the talk with a breif survey of detection prospects in current and future networks, both terrestrial and space-based. |
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12.12.2024 13:30 S2|11 10 |
Dr. Zhen Li (TU Darmstadt) Some advances in many-body perturbation theory and ab initio half-lives of r-process waiting point nuclei The Rayleigh-Schrödinger (RS) formulation of many-body perturbation theory (MBPT) has been widely used in nuclear structure calculations, while the Brillouin-Wigner (BW) formulation has received comparatively less attention in the theoretical nuclear physics community. In the first part of this talk, I will present recent developments and applications of BW MBPT for closed- and open-shell nuclei. The beta-decay half-lives of neutron-rich nuclei with magic neutron numbers, a critical input for r-process simulations, remain largely unknown experimentally. In the second part of this talk, I will show ab initio predictions for the beta-decay half-lives of N=50 isotones. |
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14.11.2024 13:30 S2|11 10 |
Prof. Dr. David Blaschke (Universität Wroclaw) Twin stars and the QCD phase diagram It has been suggested that the observation of pulsars with the same mass but significantly different radii (twin stars) would prove that the existence of a critical endpoint in the QCD phase diagram since this phenomenon requires a strong phase transition in cold neutron star matter. We explore whether such a phase transition in neutron star cores, possibly coupled with a secondary kick mechanism such as neutrino or electromagnetic rocket effect, may provide a formation path for isolated and eccentric millisecond pulsars (MSPs). We show that a gravitational mass loss of approximately 0.01 solar masses suffices to produce an eccentricity of the order of 0.1 without the need of a secondary kick mechanism. We also show that in warm supernova and merger matter, thermal twin stars can be formed, even when the mass-radius diagram of cold neutron stars has no twins. We speculate about a correlation of the thermal twin phenomenon with the supernova explodability of massive blue supergiant stars and discuss the accessibility of color superconducting quark matter phases in heavy-ion collisions. |
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31.10.2024 13:30 S2|11 10 |
Patrick Cook (MSU) Parametric Matrix Models: Model Emulation, Model Discovery, and General Machine Learning Parametric Matrix Models (PMMs) are a new class of implicit machine learning algorithms and techniques which aim to learn the underlying governing equations of data. This talk will give a conceptual and practical overview of PMMs for model emulation, highlight some ongoing work in using PMMs for model discovery, and show results demonstrating state-of-the-art parameter efficiency in general machine learning tasks. Finally, I will discuss ongoing theoretical efforts to extend PMMs to state-vector emulation and nonlinear problems as well as to unify PMMs with existing methods such as Dynamic Mode Decomposition, Proper Orthogonal Decomposition, and Eigenvector Continuation in a single framework. |
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24.10.2024 13:30 S2|11 10 |
Prof. Dr. Fernando Romero-López (Universität Bern) Hadronic resonances from Lattice QCD The majority of known hadrons in the low-energy QCD spectrum are resonances observed in multi-particle scattering processes. First-principles determinations of the properties of these unstable hadrons are a crucial goal in lattice QCD calculations. Significant progress has been made in developing, implementing and applying theoretical tools that connect finite-volume lattice QCD quantities to scattering amplitudes, enabling determination of masses and widths of various hadronic resonances. In this talk, I will discuss recent advances in lattice QCD studies of meson-baryon resonances, including the Delta(1232) and Lambda(1405) resonances, as well as three-hadron resonances such as the doublycharmed tetraquark. |
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02.10.2024 13:30 S2|11 10 |
Dr. Rajeev Singh (West University of Timisoara, Romania) Stochastic relativistic advection-diffusion equation from the Metropolis We study an approach to simulating the stochastic relativistic advection-diffusion equation based on the Metropolis algorithm. We show that the dissipative dynamics of the boosted fluctuating fluid can be simulated by making random transfers of charge between fluid cells, interspersed with ideal hydrodynamic time steps. The random charge transfers are accepted or rejected in a Metropolis step using the entropy as a statistical weight. This procedure reproduces the expected strains of dissipative relativistic hydrodynamics in a specific (and non-covariant) hydrodynamic frame known as the density frame. Numerical results, both with and without noise, are presented and compared to relativistic kinetics and analytical expectations. An all order resummation of the density frame gradient expansion reproduces the covariant dynamics in a specific model. In contrast to all other numerical approaches to relativistic dissipative fluids, the dissipative fluid formalism presented here is strictly first order in gradients and has no non-hydrodynamic modes. We will also present the extension to relativistic viscous hydrodynamics and its comparison with BDNK formalism. |
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18.07.2024 13:30 S2|11 10 |
Prof. Dr. André da Silva Schneider (Universidade Federal de Santa Catarina) Equation of State Effects in Astrophysical Phenomena Uncertainties in our knowledge of the properties of dense matter near and above nuclear saturation density are one of the main sources of variation in multi-messenger signatures predicted for the core-collapse of massive stars and the properties of the resulting remnants. In this talk I will discuss how variations in the equation of state of dense nuclear matter affect the core collapse of massive stars and what we can hope to learn about the equation of state from a future galactic supernova detection in neutrinos and gravitational waves. |
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11.07.2024 13:30 S2|11 10 |
Oscar Garcia Montero (Universität Bielefeld) 3D initial energy and charge deposition in Heavy Ion Collisions within a saturation-based formalism I present our novel 3D resolved model for the initial state of ultrarelativistic heavy-ion collisions, based on the $k_\perp$-factorized Color Glass Condensate hybrid approach. The McDIPPER framework responds to the need for a rapidity-resolved initial-state Monte Carlo event generator which can deposit the relevant conserved charges (energy, charge and baryon densities) both in the midrapidity and forward/backward regions of the collision. This event-by-event generator computes the gluon and (anti-) quark phase-space densities using the IP-Sat model, from where the relevant conserved charges can be computed directly. In the present work we have included the leading order contributions to the light flavor parton densities. In this talk, I present our studies on the emergence of long-range rapidity correlations in nuclear collisions due to the inclusion of event-by-event nucleonic and sub-nucleonic fluctuations in the initial state. Additionally, I will discuss current research avenues to expand the formalism, focusing on the effect of low-energy nuclear structure on the energy and charge deposition, and the connections this may have with the physics of Deeply Inelastic Scattering-like experiments, such as in ultra peripheral collisions at the LHC and the upcoming Electron Ion Collider. |
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04.07.2024 13:30 S2|11 10 |
Prof. Dr. Dean Lee (Michigan State University) Parametric Matrix Models I give an introduction to a new machine learning approach called parametric matrix models, which are based on the matrix equations of quantum physics rather than the biology of neurons. Rather than fitting output functions according to some specified form, PMMs learn the underlying equations that produce the desired output, similar to how physics problems are solved. I discuss the connection to eigenvector continuation and reduced basis methods, show the proof of the universal function approximation theorem, and then go through several applications to scientific computing as well as more general machine learning applications related to image recognition. |
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26.06.2024 13:30 S2|11 10 |
Dr. Shinya Wanajo (Albert Einstein Institute Potsdam) Production of heaviest nuclei in neutron star mergers The origin of r-process elements such as gold and uranium has long been a mystery in astrophysics. The discovery of an electromagnetic counterpart (kilonova) associated with the gravitational wave event GW170817 has confirmed that neutron star mergers are sites where the r-process occurs. However, whether neutron star mergers are the dominant sources of r-process nuclei in the universe remains uncertain. In this presentation, I will share our latest nucleosynthesis study results, which are based on magnetohydrodynamic simulations of neutron star mergers, as well as other potential sites such as black hole-neutron star mergers and collapsar. |
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13.06.2024 13:30 S2|11 10 |
Dr. Melissa Mendes (TU Darmstadt) Investigating the nuclear equation of state from neutron star cooling and mass-radius information Investigating the behavior of the nuclear equation of state (EOS) is an open research question. In particular, the study of neutron stars has been especially fruitful to probe the EOS at densities above saturation thanks to observations of its properties such as mass, radius, tidal deformability and temperature. In this talk, I discuss two works dealing with constraining the neutron star EOS. First, I use observations of the luminosity of fast cooling transiently-accreting neutron stars to investigate a possible first-order quark-hadron phase transition. Then, I discuss how new NICER mass-radius data combined with gravitational wave observations and chiral effective theory constraints provide information for the neutron star EOS. |
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06.06.2024 13:30 S2|11 10 |
Dr. Andrea Porro (TU Darmstadt) Ab initio description of monopole resonances in light- and medium-mass nuclei Giant monopole resonances have a long-standing theoretical importance in nuclear structure. The interest resides notably in the so-called breathing mode that has been established as a standard observable to constrain the nuclear incompressibility. The Random Phase Approximation (RPA) within the frame of phenomenological Energy Density Functionals (EDF) has become the standard tool to address giant resonances and extensive studies, have been performed throughout the years. A proper study of collective excitations within the ab initio framework is, however, missing. Additionally, the ab initio many-body methods developed over the past two decades encounter limitations when it comes to dealing with excited-state properties. In this perspective, I will present a systematic ab initio predictions of (giant) monopole resonances. Ab initio Quasiparticle-RPA (QRPA) and Projected Generator Coordinate Method (PGCM) calculations of monopole resonances are compared in light- and mid-mass closed- and open- shell nuclei. Monopole resonances represent the starting point for exploring higher multipolarities, the goal in the medium term being to establish PGCM and QRPA as complementary tools in the development of a fundamental theory of nuclear excitations. |
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16.05.2024 13:30 S2|11 10 |
Dr. Aurore Betranhandy (Albert Einstein Institute Potsdam) Neutrino and axion impact in the early phase of core-collapse supernova simulations Core-collapse supernova simulations are cornerstone in our understanding of stellar evolution, and global nucleosynthesis. While we now achieve consistent explosions in multi-dimensional simulations, a lot of approximations are still present in our codes, especially in the micro-physical aspect, such as neutrino interactions and possible axion emission. In this talk I will present my research on the impact of these approximations in our simulations, and how the resulting explosion and signal can vary depending on the micro-physics we chose to include. I will more specifically talk about the impact of the proto neutron star's early cooling, with an accent on a cooling process through heavy-lepton neutrinos and potentially axions, on the final explosion. |
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02.05.2024 13:30 S2|11 10 |
Prof. Dr. Silas Beane (University of Washington) Unnuclear physics at large charge After reviewing the unitary Fermi gas and relevant aspects of non-relativistic conformal symmetry (Schrödinger symmetry), I will introduce the superfluid effective field theory (EFT) that describes the Fermi gas at and near unitarity in the far infrared. This EFT admits a large-charge expansion which allows the systematic computation of large-charge n-point functions. I will discuss the potential relevance of the large-charge formalism to the study of special nuclear reactions with many low-energy neutrons in the final state. |
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18.04.2024 13:30 S2|11 10 |
Dr. Lotta Jokiniemi (TRIUMF) Neutrinoless double-beta decay and how to probe it with muon capture Neutrinoless double-beta decay is a hypothetical weak-interaction process in which two neutrons inside an atomic nucleus simultaneously transform into protons and only two electrons are emitted. Since the electrons are emitted without accompanying antiparticles, the process violates the lepton-number conservation and requires that neutrinos are Majorana particles, hence providing unique vistas in the physics beyond the Standard Model of particle physics. The potential to discover new physics drives ambitious experimental searches around the world. However, extracting interesting physics from the experiments relies on nuclear-theory predictions, which remain a major obstacle. I will talk about two approaches to tackle this problem. First, I will discuss the evaluation of recent effective-field-theory corrections to the operators and their effect on the theory predictions based on phenomenological nuclear many-body methods. Then, I will discuss first-principles calculations of muon capture in light nuclei, which have the potential to shed light on the high-momentum-exchange currents driving neutrinoless double-beta decay. |
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08.02.2023 13:30 S2|11 10 |
Prof. Dr. Rob Pisarski (Brookhaven National Laboratory) Why the chiral phase transition for three light flavors is so interesting In QCD, the eta prime meson is heavy because the breaking of the anomalous U_A(1) symmetry is large. A simple argument suggests that it should then be easy to see a first order chiral transition for light quarks. Nevertheless, numerical simulations on the lattice see no evidence for such a first order chiral transition. I suggest that this occurs because the usual power counting for anomalous operators is more subtle than expected. This leads to numerous predictions for different numbers of quark flavors. The case of a single flavor is especially interesting. It also suggests novel experimental signals. |
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25.01.2023 13:30 S2|11 10 |
Dr. Isak Svensson (TU Darmstadt) Bayesian uncertainty quantification in ab initio nuclear theory The theory of the strong interaction – quantum chromodynamics (QCD) – is unsuited to practical calculations of nuclear observables and approximate models for nuclear interaction potentials are required. In contrast to phenomenological models, chiral effective field theories (chiral EFTs) of QCD grant a handle on the theoretical uncertainty arising from the truncation of the chiral expansion. Uncertainties in chiral EFT are preferably quantified using Bayesian inference, but quantifying reliable posterior predictive distributions for nuclear observables presents several challenges. First, chiral EFT is parametrized by unknown low-energy constants (LECs) whose values must be inferred from low-energy data of nuclear structure and reaction observables. There are 31 LECs at fourth order in Weinberg power counting, leading to a high-dimensional inference problem which I approach by developing an advanced sampling protocol using Hamiltonian Monte Carlo (HMC). This allows me to quantify LEC posteriors up to and including fourth chiral order. Second, the chiral EFT truncation error is correlated across independent variables such as scattering energies and angles; I model correlations using Gaussian processes. Third, the computational cost of computing few- and many-nucleon observables typically precludes their direct use in Bayesian parameter estimation as each observable must be computed in excess of 10^5 times during HMC sampling. However, eigenvector-continuation emulators today provide the necessary leverage to include observables beyond the two-nucleon sector in Bayesian inferences. In this talk I discuss the progress I made in this area during my PhD studies, presenting findings regarding the LEC inference problem as well as resulting posterior predictive distributions for nuclear observables. |
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14.12.2023 13:30 S2|11 10 |
Prof. Dr. Sören Schlichting (Bielefeld University) Collectivity in Heavy-Ion collisions – exploring the applicability of fluid dynamics far from equilibrium High-energy heavy-ion collisions provide a unique environment to explore the properties of strong-interaction matter under extreme conditions. Since the theoretical description of the complex reaction dynamics from the underlying theory of QCD poses an outstanding challenge, a macroscopic description in relativistic hydrodynamics is commonly employed to describe the emergence of collective phenomena in heavy-ion collisions. In this talk, we will discuss recent progress to understand the non-equilibrium dynamics of QCD plasmas from kinetic theory, and assess the range of applicability of hydrodynamics as an effective description for non-equilibrium systems. |
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07.12.2023 13:30 S2|11 10 |
Mariam Gogilashvili (Florida State University) Predicting Which Massive Stars Explode At the end of their lives, most massive stars undergo core collapse. Some stars explode as a core-collapse supernova (CCSN) explosion leaving behind neutron stars (NS) while others fail to explode and collapse to stellar-mass black holes (BH). One of the major challenges in CCSN theory is to predict which stars explode and which fizzle. We develop an analytic force explosion condition (FEC) to predict which massive stars explode. The FEC depends upon four dimensionless parameters only: 1. net neutrino heating deposited in the gain region, 2. neutrino opacity that parameterizes the neutrino optical depth in the accreted matter near the neutron-star surface, 3. the integrated buoyant driving, and 4. the radial component of the Reynolds stress. The FEC promises to be an accurate explosion condition for multi-dimensional simulations as well as being useful diagnostic to measure a “distance” to explosion. I will present a progress in validating the FEC with multi-dimensional simulations and discuss potential to expand the model by including additional effects that may be important to predict explosions in nature. |
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30.11.2023 13:30 S2|11 10 |
Dr. Marta Molero (Universita degli studi di Trieste) Chemical evolution of neutron-capture elements across the Milky Way Modelling the evolution of the elements in galaxies of different morphological types is a multidisciplinary and challenging task. Chemical evolution simulations must be able to follow ~ 13 billion years of evolution of a galaxy and also to keep track of the elements synthesized and ejected from every astrophysical site of interest. In this talk, I will give a general overview of the Chemical Evolution of Galaxies field describing both its aims and explaining which are the basic ingredients necessary to build a Chemical Evolution simulation. I will then focus on the study of the evolution of heavy elements abundances. The majority of elements beyond the Fe peak are produced by neutron capture processes which can be rapid (r-process) or slow (s-process) with respect to the beta-decay in nuclei. Understanding which are the astrophysical formation sites of these two processes has become one of the major challenges in chemical evolution. In this talk, I will first present the main steps done in chemical evolution simulations to understand the origin of neutron capture elements and then I will show results from our latest work. |
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23.11.2023 13:30 S2|11 10 |
Dr. Johannes Weber (Humboldt-Universität Berlin) Hard Probes of Hot Nuclear Matter The hot nuclear medium that permeated the early universe can be studied experimentally with heavy-ion collisions and through various theoretical approaches. New or upgraded experiments turn our attention to hard processes and a more fine-grained resolution of this primordial state of matter. In this endeavor quarkonia, open heavy flavors, and jets turn out to be versatile probes, which are usually described through models based on resummed perturbative QCD, AdS, and effective field theories. The lattice provides nonperturbative input and constraints to such models. In-medium bottomonia, the complex static quark-antiquark potential, as well as the heavy-quark momentum and the jet transverse momentum diffusion transport coefficients are key quantities where lattice gauge theory has recently achieved significant progress with major impact for heavy-ion phenomenology. I review these lattice results, relate them to phenomenological applications, and close with an outlook towards expectations for the next few years. |
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16.11.2023 13:30 S2|11 10 |
Dr. Theo F. Motta (TU Darmstadt and JLU Giessen) A Stability Analysis of Inhomogeneous Phases in QCD Understanding the phase structure of Quantum Chromodynamics (QCD) is of paramount importance for nuclear and particle physics. At large densities and low temperatures, many complex phases are expected to appear. This is where the lattice sign problem is unavoidable and extrapolation methods such as Taylor expansions are out-of-bounds. Alongside colour-superconductivity, quarkyonic matter, and so on, the possibility of a crystalline phase has been studied for over twenty years. In simplified models of QCD such as NJL or quark-meson models, these phases are present. However, no unambiguous determination exists that they appear in QCD. In this talk, I will discuss our efforts to develop a method of stability analysis that is compatible with full QCD via Dyson-Schwinger Equations. |
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09.11.2023 13:30 S2|11 10 |
Martin Obergaulinger (Valencia University) Core-collapse supernovae with magnetic jets Magnetic fields are a common feature of both the progenitors of core-collapse supernovae, i.e., massive stars, and of their remnants, neutron stars. If combined with rapid rotation, they can affect the explosion dynamics and eject a part of the gas in the form of jets along the rotational axis. Besides the high explosion energies, these events also differ from the majority of neutrino-driven supernovae by their nucleosynthetic yields and observables like the gravitational-wave signal. I will present recent simulations of a set of three-dimensional simulations combining magnetohydrodynamics and neutrino transport in which explosions with different degree of magnetic influence occur and highlight some of the key processes that determine the outcome. |
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10.08.2023 14:00 S2|11 10 |
Dr. Aman Abhishek (Institute of Mathematical Sciences, Chennai, India) Towards a universal description of hadronic phase of QCD Mean-field model quantum field theories of hadrons were traditionally developed to describe cold and dense nuclear matter and are by now very well constrained from the recent neutron star merger observations. We show that when augmented with additional known hadrons and resonances but not included earlier, these mean-field models can be extended beyond its regime of applicability. Calculating some specific ratios of baryon number susceptibilities for finite temperature and moderate values of baryon densities within mean-field approximation, we show that these match consistently with the lattice QCD data available at lower densities, unlike the results obtained from a non-interacting hadron resonance gas model. We also estimate the curvature of the line of constant energy density, fixed at its corresponding value at the chiral crossover transition in QCD, in the temperature-density plane. The number density at low temperatures and high density is found to be about twice the nuclear saturation density along the line of constant energy density of 348 +- 41 MeV/fm3. Moreover from this line we can indirectly constrain the critical end-point of QCD to be beyond 597 MeV mu_B for temperature 125 MeV. |
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28.06.2023 14:00 S2|11 10 |
Prof. Dr. Mark Alford (Washington University, St. Louis) Is nuclear matter in neutron star mergers driven out of equilibrium? In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on chemical (beta) equilibration and its consequences such as bulk viscosity and damping of oscillations. |
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22.06.2023 14:00 S2|11 10 |
Prof. Dr. Dam T. Son (University of Chicago) Nonrelativistic conformal field theory and nuclear reactions We develop a formalism of nonrelativistic conformal field theory, which is then used to describe neutrons at low energies. We show that the rates of nuclear reactions with emission of a few neutrons in the final state show a power-law behavior in the kinematic region where the emitted neutrons have almost the same momentum. We show how corrections to this power-law behavior can be computed using conformal perturbation theory. |
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15.06.2023 14:00 S2|11 10 |
Assistant Prof. Dr. Luka Leskovec (Universität Ljubljana) Baryonic Resonances in Lattice QCD In recent decades, lattice QCD has been crucial in understanding the Standard Model. As a new era of experiments centered around nuclear physics begins, we also focus on baryons and their phenomena. In this talk, I will motivate some reasons for a deeper understanding of baryons from first principles QCD. After a brief overview of the formalism and the intricacies involved with baryons, I will present our lattice QCD calculation of the lightest baryonic resonance, the (1232) – mass and decay width. |
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25.05.2023 14:00 S2|11 10 |
PD Dr. Sara Collins (Universität Regensburg) Properties of the baryon octet from lattice QCD Numerous ongoing experimental investigations into physics beyond the Standard Model focus on nucleons as fundamental probes, prompting extensive efforts to extract nucleon structure observables on the lattice. This includes the determination of quantities like the weak charges and axial form factors. However, it is also interesting to extend such studies to hyperons, which have received less attention. Exploring the properties of hyperons provides valuable insights into the SU(3) flavor symmetry encoded in low-energy effective field theory descriptions. Moreover, studying their weak decays offers alternative means of determining the elements of the CKM matrix. As a first step we determine the spectrum, weak charges and sigma terms of the baryon octet controlling all sources of systematic uncertainty. |
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24.04.2023 15:00 S2|11 207 |
Frederic Noël (Uni Bern) Mu -> e conversion, LFV pseudoscalar decays, and nuclear charge densities Mu -> e conversion in nuclei gives one of the leading limits on BSM lepton-flavor violating (LFV) processes. In this process a muon bound to a nucleus converts into an electron without neutrinos. Upcoming measurements call for a more consistent theoretical description of mu -> e conversion, which can be done model independently using an effective field theory frame work in terms of effective BSM operators. As it turns out, the relevant operators for the spin dependent part of mu -> e conversion also mediates LFV pseudoscalar decays, which makes it possible to relate these processes and their experimental limits. Furthermore for the treatment of the bound state physics appearing in mu -> e conversion, quantifiable knowledge on the charge densities of the considered nuclei is needed. In this talk I will give an overview over our ongoing work on mu -> e conversion, including some recent results regarding LFV pseudoscalar decays, as well as the determination of nuclear charge densities from electron scattering. |
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20.04.2023 14:00 S|11 10 |
Dr. Saga Aurora Säppi (TU München) Exploring extremely dense matter with perturbative QCD With LIGO and its friends observing colliding neutron stars, and astrophysicists measuring their radii and masses with unprecedented precision, understanding how dense QCD matter behaves is a particularly timely goal. I will approach this from the side of (very-)high-density theory: How do first-principles calculations in dense QCD in the small-coupling limit work, and how have they advanced in the last few years? Some of the advancements I will discuss in this talk include an efficient and simple way to incorporate the effects of quark masses in perturbative calculations, particularly useful for near-future calculations of the bulk viscosity, as well as an ongoing computation of the next-to-next-to-next-to-leading order pressure of cold dense QCD, where there are both concrete recent (and upcoming) results for the self-energy as well as improved theoretical methods necessary for finishing the full computation. |
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26.01.2023 14:00 via Zoom |
Dr. Zhonghao Sun (Oak Ridge National Laboratory) Ab-initio computation of exotic nuclei Precise and predictive calculations of the atomic nuclei from realistic nuclear force help us to understand how the fundamental interaction leads to the emergence of various exotic phenomena. The advances in computational power, emerging machine learning technology, and the development of many-body methods make it possible to perform uncertainty quantification and sensitivity analyses in the nuclear structure calculations. In this talk, I will report the progress of the ab-initio coupled-cluster method in describing spherical and deformed atomic nuclei. I will also introduce the quantified predictions of the neutron skin thickness of 208Pb and the drip line of oxygen isotopes. |
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15.12.2022 15:00 via Zoom |
Dr. Agnieszka Sorensen (INT Seattle) The speed of sound of dense nuclear matter from heavy-ion collisions The equation of state (EOS) of dense nuclear matter has been the center of numerous research efforts over the years. While numerous studies indicate that the EOS is relatively soft around the saturation density of nuclear matter, recent analyses of neutron star data strongly suggest that in the cores of neutron stars, where densities may reach several times that of normal nuclear matter, the EOS becomes very stiff – so stiff, in fact, that the speed of sound squared may substantially exceed the conformal limit of 1/3. This striking behavior inspires the research I will present in this talk. I will discuss a novel way of using higher moments of the baryon number distribution, measured in experiments, to infer the speed of sound in dense nuclear matter created in low-energy heavy-ion collisions. I will then present the framework I developed to enable comprehensive hadronic transport studies of the influence of the dense nuclear matter EOS on experimental observables, and I will discuss implications for the speed of sound of dense nuclear matter based on a recent analysis using this framework. |
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24.11.2022 14:00 S2|11 10 |
Prof. Dr. Owe Philipsen (Goethe Universität Frankfurt) Chiral spin symmetry and the QCD phase diagram Recently, an emerging chiral spin symmetry was discovered in the multiplets of lattice QCD hadron correlators for a temperature window above the chiral crossover. This symmetry is larger than the expected chiral symmetry. It can only be approximately and dynamically realised when colour-electric quark-gluon interactions dominate the quantum effective action. This suggests the chiral spin symmetric regime to be of a hadron-like rather than partonic nature. After a brief review of the symmetry, I show independent evidence from meson screening masses and the pion spectral function, which support this picture. Finally, I discuss how this chiral spin symmetric band may continue across the QCD phase diagram, where it may smoothly connect to quarkyonic matter at low temperatures and high densities. |
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17.11.2022 14:00 S2|08 171 (Uhrturmhörsaal) |
Dr. Marcel Schmidt (d-fine) How to save the financial system: My journey from Physics to Risk Management @ d-fine For over 3 years I have worked at d-fine, a leading consultancy for analytically demanding topics from branches like finance, energy industry or manufacturing. Early in my career, I have specialized in market risk management. In our projects, we help banks to secure against price fluctuations, using state-of-the-art methods from mathematics, machine learning, and modern software development. In this talk, I would like to provide an impression on my career path and show how we as physicists contribute to a more secure financial system. |
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10.11.2022 14:00 S2|11 10 |
Prof. Dr. Frithjof Karsch (Universität Bielefeld) QCD Phase Diagram and the Equation of State of Strong-Interaction Matter Lattice QCD calculations at non-zero temperature and with non-vanishinq chemical potentials provide a powerful framework for the analysis of the phase structure of strongly interacting matter. Such calculations allow the determination of the crossover transition region at QCD with physical quark masses as well as the determination of the true chiral phase transition in the limit of vanishing light quark masses. We present results on the determination of the pseudo-critical and chiral phase transition temperatures as well as a new, high statistics determination of the QCD equation of state. We point out their importance for constraining the location of a possible critical end point in the QCD phase diagram. We furthermore present a new, high statistics determination of the QCD equation of state. |
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27.10.2022 14:00 S2|11 10 |
Dr. Renwick James Hudspith (GSI) A complete lattice QCD determination of the hadronic light-bylight scattering contribution to the muon g-2 The g-2 of the muon provides a high-precision test of the Standard Model of particle physics, and a possible window into beyond the Standard Model physics. Currently, there is some tension between the theoretical prediction of this quantity and experiment. As experimental precision continues to improve it is paramount for theoretical computations to do so also, in hope of resolving this tension. One of the most poorly-known contributions to the theory calculation of the muon g-2 comes from hadronic light-bylight scattering. I will present an overview of our measurement of this contribution using lattice QCD techniques, where we have obtained the most precise determination to date. |
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23.09.2022 14:00 S2|11 10 & Zoom |
Prof. Dr. Baha Balantekin (University of Wisconsin) Collective Neutrino Oscillations and Quantum Entanglement Entanglement of constituents of a many-body system is a recurrent feature of quantum behavior. Quantum information science provides tools, such as the entanglement entropy, to help assess the amount of entanglement in such systems. Many-neutrino systems are present in core-collapse supernovae, neutron star mergers, and the Early Universe. Recent work in applying the tools of quantum information science to the description of the entanglement in astrophysical many-neutrino systems is presented, in particular the connection between entropy and spectral splits in collective neutrino oscillations is elaborated. |
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14.07.2022 14:00 S2|11 10 & Zoom |
Prof. Dr. Derek Teaney (Stony Brook) Dynamics of the O(4) critical point in QCD To motivate the simulations I review Lattice data on the chiral phase transition in QCD. Then I discuss the hydrodynamics of the chiral phase transition, reviewing the appropriate dynamical equations above, below, and during the phase transition. Then I present a simulation of the dynamics of the phase transition, which shows how goldstone modes appear dynamically. Finally I discuss soft pions in heavy ion collisions, which are enhanced relative to normal hydrodynamic simulations of heavy ion collisions. I suggest that this reflects the fingerprints of the O(4) critical point. |
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07.07.2022 14:00 S2|11 10 & Zoom |
Prof. Dr. Lorenz von Smekal (Justus-Liebig-Universität Gießen) Real-time methods for spectral functions The real-time methods discussed and compared in this talk include classical-statistical lattice simulations, the Gaussian state approximation (GSA), and the functional renormalization group (FRG) formulated on the Keldysh closed-time path. The quartic anharmonic oscillator coupled to an external heat bath after Caldeira and Leggett thereby serves as an illustrative example where a benchmark solution can be obtained from exact diagonalization with constant Ohmic damping. To extend the GSA to open systems, we solve the corresponding Heisenberg-Langevin equations in the Gaussian approximation. For the real-time FRG, we introduce a novel general prescription to construct causal regulators based on introducing scale-dependent fictitious heat baths. As first field theory applications we have used our real-time FRG framework to calculate dynamical critical exponents for different dynamics. |
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04.07.2022 15:00 S2|11 10 & Zoom |
Dr. Robert Pisarski (Brookhaven National Laboratory) A potpourri in extreme QCD I discuss some combination of topics in SU(N) gauge theories at nonzero temperature and density, including: the exact solution of the low energy excitations for cold, dense quarks in 1+1 dimensions (you'll learn what a Luttinger liquid is); how to represent timelike Wilson loops in Hamiltonian form (bit obvious after the fact); configurations with topological charge 1/N in SU(N) gauge theories without dynamical quarks |
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09.06.2022 14:00 S2|11 10 & Zoom |
Carolyn Raithel (Princeton Center for Theoretical Science) Probing the Dense-Matter Equation of State with Neutron Star Mergers Binary neutron star mergers provide a unique probe of the dense-matter equation of state (EOS) across a wide range of parameter space, from the cold EOS during the inspiral to the finite-temperature EOS following the merger. In this talk, I will discuss the influence of finite-temperature effects on the post-merger evolution of a neutron star coalescence. I will present a new set of neutron star merger simulations, which use a phenomenological framework for calculating the EOS at arbitrary temperatures and compositions. I will show how varying the properties of the particle effective mass affects the thermal profile of the post-merger remnant and how this, in turn, and influences the post-merger evolution. Finally, I will discuss several ways in which a future measurement of the post-merger gravitational waves can be used to constrain the dense-matter EOS. |
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02.06.2022 14:00 S2|11 10 & Zoom |
Dr. Joanna Sobcyk (Uni Mainz) Nuclear ab initio studies for neutrino oscillations We are entering an era of high-precision neutrino oscillation experiments (T2HK, DUNE), which potentially hold answers to some of the most exciting questions in particle physics. Their scientific program requires a precise knowledge of neutrino-nucleus interactions coming from fundamental nuclear studies. Ab initio many-body theory has made great advances in the last years and is able to give relevant predictions for medium-mass nuclei important for the neutrino experiments. In my talk I will give an overview of the recent progress that has been made in describing neutrino-nucleus scattering within the ab-initio coupled-cluster framework, combined with the Lorentz integral transform. These techniques open the door to obtaining nuclear responses (and consequently cross-sections) for medium-mass nuclei starting from first principles. |
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31.05.2022 16:00 S2|11 10 & Zoom |
Dr. Aleksas Mazeliauskas (CERN) Many-body QCD phenomena in high-energy proton and nuclear collisions The emergence of macroscopic medium properties over distances much smaller than a single atom is a fascinating and non-trivial manifestation of the many-body physics of Quantum Chromodynamics in high-energy nuclear collisions. The observation of collective particle behaviour in collisions of heavy-ions at the Relativistic Heavy Ion Collider at BNL and the Large Hadron Collider at CERN is strong evidence that a new exotic phase of matter called the Quark-Gluon Plasma is created in these large collision systems. However, the striking discovery of the very same collective phenomena in much smaller systems of proton-proton and proton-lead collisions at the LHC has confounded heavy-ion physics expectations and is not predicted by the conventional high-energy physics picture of elementary collisions. One of my main research goals is to uncover the physical origins of this universal macroscopic behaviour. In this talk I will review the recent progress and future plans in developing theoretical description and experimental tests of these effects within the non-Abelian quantum field theory of strong interactions. |
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12.05.2022 14:00 S2|11 10 & Zoom |
Prof. Dr. Thomas Schäfer (NC State University) Stochastic fluid dynamics: Effective actions and new numerical tools Recent interest in stochastic fluid dynamics is motivated by the search for a critical point in the QCD phase diagram. I will discuss old ideas about effective actions that have recently received new interest, and some new ideas about how to implement stochastic fluid dynamics in numerical simulations. |
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10.02.2022 14:00 Zoom |
Lotta Jokiniemi (University of Barcelona) What Can We Learn from Double-Beta Decay and Ordinary Muon Capture? Observing neutrinoless double-beta (0vbb) would undoubtedly be one of the most anticipated breakthroughs in modern-day neutrino and nuclear physics. This is highlighted by the number of massive experiments worldwide trying to detect the phenomenom, as well as the efforts of numerous theory groups trying to probe the process from different theory frameworks. When observed, the lepton-number-violating process would provide unique vistas beyond the Standard model of particle physics. However, the half-life of the process depends on coupling constants whose effective values are under debate, and nuclear matrix elements (NMEs) that have to be extracted from theory. Unfortunately, at present different many-body calculations probe matrix elements whose values disagree by more than a factor of two. Hence, it is crucial to gain a better understanding on both the coupling constants and the NMEs in order to plan future experiments and to extract the beyond-standard-model physics from the experiments. In my seminar I will discuss how the theory predictions can be improved either directly by investigating corrections to the 0vbb decay matrix elements, or indirectly by studying alternative processes that can be or have been measured. First, I will introduce our recent work on a new leading-order correction to the standard 0vbb-decay matrix elements in heavy nuclei. Then, I will discuss the potential of ordinary muon capture as a probe of 0vbb decay, and discuss the results of our recent muon-capture studies. |
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03.02.2022 14:00 Zoom |
Laura Sagunski (Goethe Universität Frankfurt) Gravitational Waves from the Dark Side of the Universe The first ever direct detections of gravitational waves from merging black holes and neutron stars by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector have opened a fundamentally new window into the Universe. Gravitational waves from binary mergers are high precision tests of orbital dynamics and provide an unprecedented tool to probe fundamental physics. Not only do they allow to test gravity under extreme conditions, but also to address the very fundamental open questions in the evolution of our Universe, namely the mysteries of dark matter and dark energy (or possible modifications of general relativity). In my talk, I will show how we can turn binary mergers into cosmic labs where we can test the very foundations of general relativity and explore the existence of new interactions and particles, like axions, which could be the dark matter. |
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16.12.2021 14:00 Zoom |
Felipe Attanasio (Uni Heidelberg) QCD equation of state via the complex Langevin method The equation of state of hadronic matter is of high importance for many fields, ranging from heavy-ion collisions to neutron stars. Non- perturbative methods to simulate QCD encounter difficulties at finite chemical potential mu due to the so-called sign problem. We employ the complex Langevin method to circumvent this problem and carry out simulations at a variety of values for temperature and mu. We present results on the pressure, energy and entropy equations of state, as well as a numerical observation of the Silver Blaze phenomenon. |
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09.12.2021 14:00 Zoom |
Vittorio Soma (CEA Saclay) A novel many-body method for the ab initio description of doubly open-shell nuclei Recent developments in many-body theory and in the modelling of nuclear Hamiltonians have enabled the ab initio description of a considerable fraction of atomic nuclei up to mass A~100. In this context, one of the main challenges consists in devising a method that can tackle doubly open-shell systems and at the same time scales gently with mass number. This would allow both to access all systems below A~100 and to open up perspectives for extending ab initio calculations to the whole nuclear chart. In this seminar I will present a recently proposed many-body approach that aims towards this objective. After introducing the formalism based on a multi-reference perturbation theory [1], I will discuss the first numerical applications [2,3] together with considerations on the state of the art and future perspective in ab initio nuclear structure. [1] M. Frosini et al., arXiv:2110.15737 [2] M. Frosini et al., arXiv:2111.00797 [3] M. Frosini et al., arXiv:2111.01461 |
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25.11.2021 14:00 Zoom |
Nicolas Wink (TU Darmstadt) Elementary correlation functions and their applications in QCD In this talk we explore the calculation of elementary correlation functions in the context of QCD. We consider these correlation functions in Euclidean and Minkowski space-time. For the latter we consider direct calculations based on dimensional regularization in Dyson-Schwinger equations in a scalar theory and Yang-Mills. Additionally, we present results from analytic continuation of Euclidean lattice data based on Gaussian Process Regression in full QCD. Afterwards we turn our attention to the calculation of transport coefficients in Yang-Mills, based on gluon spectral functions obtained previously. In the last part of the talk we consider field dependencies in functional Renormalization Group equations. We focus in particular on technical challenges at high densities and how to overcome them. |
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18.11.2021 14:00 Zoom |
Andreas Ipp (Vienna University of Technology) Simulating the Glasma stage in heavy ion collisions The earliest stage right after the collision of ultrarelativistic heavy ions is known as the Glasma stage. It is characterized by strong anisotropic color fields and forms the precursor of the quark-gluon plasma. In this talk, I present our approach to simulating the Glasma using a colored particle-in-cell simulation. With this method, we can access the full 3+1 dimensional space-time picture of the collision process. These simulations are inherently plagued by numerical Cherenkov instability, and we show how an improved action can cure this instability using a semi-implicit scheme. Simulation results can be checked in a dilute limit against analytic calculations. I will present results for observables such as the rapidity profile or momentum broadening of jets within the Glasma stage. |
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28.10.2021 14:00 Zoom |
Weiguang Jiang (Chalmers) Exploring non-implausible nuclear-matter predictions with delta-full chiral interactions Advances in quantum many-body methods and computing allow us to study the finite nuclei and infinite nuclear matter with realistic interaction models based on chiral effective field theory. We develop the nuclear matter emulators and introduce the robust statistical approach called history matching to explore the non-implausible nuclear-matter predictions with chiral interactions. We studied 1.6*10^6 non-implausible interaction samples in a huge LECs domain and reveal the connection between the finite nuclei and nuclear matter saturation properties. |
