Institute for Nuclear Physics
Theory Center

Theory Seminar

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, 14:00 o'clock

Place: S2|11, Room 10

WS 22/23

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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.