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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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. |
