Seminare
| From Lattice QCD to experimental data on a sustainable path | |
| Dozent/Speaker: | Prof. Dr. Matthias F. M. Lutz (TU Darmstadt/GSI) |
| Termin/Date: | Do. 28.11.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
It is now possible and rather wide spread to do Lattice QCD simulations for selected physical quantities
at physical quark masses. Nevertheless, it is still very much desirable to gain a better understanding in how to use the chiral Lagrangian
from small quark masses, for which Lattice simulations are still rather expensive, to larger quark masses, for which Lattice simulations are much more
economical in energy consumption and budgets. While the chiral Lagrangian with three light flavors was almost declared useless by the community, the two-flavor version
with light up and down quark masses is still frequently been used, however mostly for ensembles with rather small quark masses. This reflects an unfortunate and possibly
questionable assumption on the applicability domain of the chiral Lagrangian.
In this talk I will discuss a novel development which suggests a much more favorite applicability domain of the chiral Lagrangian with not only two but also three light flavors. This would open a new path towards more sustainable approaches to QCD, which is based on Lattice QCD simulation at quark masses significantly larger than the values required to reproduce the physical pion mass and properly combined with a chiral effective field theory. The key observation which may lead to such an avenue is that the use of on-shell hadron masses inside the loop correction terms as implied by chiral Lagrangian does affect its truncation properties. We illustrate our claim at the hand of the chiral Lagrangian as applied to baryon masses and the axial vector form factors. |
| The scalar size of the pion from lattice QCD | |
| Dozent/Speaker: | Patrick Walkowiak (RUB) |
| Termin/Date: | Do. 31.10.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
The low-energy physics of nuclei resulting from the strong interaction is typically derived from chiral effective field theory, using various symmetry-preserving regularization techniques depending on the respective application. Recently, a new method, so-called gradient-flow regularization, was proposed by Hermann Krebs and Evgeny Epelbaum, aiming to provide a consistent approach to regularization that bridges different applications.
This talk lines out the application of this technique to pion-nucleon scattering in an unphysical region where chiral perturbation theory is believed to have better convergence. The presented calculations were performed within the heavy baryon approach to chiral perturbation theory up to and including order q³. The results are planned to be used as an input in the current N3LO calculations of three-nucleon forces where the pion-nucleon scattering amplitude at order q³ appears as a subprocess. |
| The scalar size of the pion from lattice QCD | |
| Dozent/Speaker: | Dr. Konstantin Ottnad (Uni Mainz) |
| Termin/Date: | Do. 17.10.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
We present a lattice QCD calculation of the pion scalar form factor and associated radii with fully controlled systematics. Lattice results are computed on a large set of 17 gauge ensembles with $N_f=2+1$ Wilson Clover-improved sea quarks. These ensembles cover four values of the lattice spacing between $a=0.049\mathrm{fm}$ and $a=0.086\mathrm{fm}$, a pion mass range of $130 - 350\mathrm{MeV}$ and various physical volumes. A precise determination of the notorious quark-disconnected contributions facilitates an unprecedented momentum resolution for the form factor, particularly on large and fine ensembles in the vicinity of physical quark mass. A large range of source-sink separations $1.0\fm \lesssim \tsep \lesssim 3.25\fm$ is used to reliably extract the relevant ground state matrix elements at vanishing and non-vanishing momentum transfer.
This allows us for the first time to obtain the scalar radii from a $z$-expansion parametrization of the $Q2$-dependence of the resulting form factors rather than a simple, linear approximation at small momentum transfer. The physical extrapolation for the radii is carried out using three-flavor NLO chiral perturbation theory to parametrize the quark mass dependence in terms of three low-energy constants, including the first lattice determination of $L_4^r$. Systematic uncertainties on the final results related to the ground state extraction, form factor parametrization as well as the physical extrapolation are accounted for via model averages based on the Akaike Information Criterion. |
| Calculating LEC Truncation Errors using a Bayesian framework | |
| Dozent/Speaker: | Hendric Jonas (RUB) |
| Termin/Date: | Do. 05.09.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Estimating the errors of LEC calculations is dependent on three main error sources: the data and corresponding uncertainties used for the calculations of LECs, the series truncation of the Hamiltonian, and uncertainties from numerical approximations and calculations in general.
In this talk, we want to take a closer look at the second source, i.e. the series truncation of EFT expansions at an order k by estimating the errors using a Bayesian approach. I will give an overview over the Bayesian theorem as well and give a detailed derivation of the truncation estimation itself. This approach is advantageous as it allows to use a method called "marginalization" allowing us to further improve results, and also gives the chance to "update" results once better data is available. Using a similar ansatz, I will additionally derive a method to estimate the series coefficients as well. In a toy model example we will conclude the presentation and talk about the effectiveness of both methods. |
| Large N_C in EFT | |
| Dozent/Speaker: | Vivien Köhler (RUB) |
| Termin/Date: | Do. 25.07.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Due to the running coupling in QCD, one cannot perform perturbative calculations for small energies. Instead of taking the coupling constant as expansion parameter, in large N_C the number of colours is used.
In this talk, I will give an overview of large N_C and some of its applications. I will start by introducing the general concept of large N_C and I will show, how the counting rules for the diagrams can be derived. Moreover, I will show some results for mesons and introduce ’t Hooft’s model in order to derive the meson spectrum. Further, I will demonstrate, why it is more difficult to derive results for baryons and discuss Witten’s approach known as the Hartree-Fock baryon picture. In the end, I will briefly show, how large N_C can be applied to ChPT. |
| Issues of Renormalization in the Few-Body Sector of Chiral EFT | |
| Dozent/Speaker: | Dan Hog (RUB) |
| Termin/Date: | Mo. 22.07.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
While renormalization in perturbative EFT is well understood, renormalization in non-perturbative EFT, particularly chiral EFT, is under longstanding debate. Over the years, different renormalization approaches have been developed, and multiple groups of scientists with opposing views on this topic have emerged.
In this talk, I introduce and discuss three different renormalization approaches in non-perturbative EFT: subtractive renormalization, cutoff EFT, and RG-invariant formulation. I begin by explaining the essence of renormalization and work my way forward step by step by first considering perturbative QFT from the perspective of renormalization before moving on to non-perturbative EFT. The renormalization approaches of non-perturbative EFT are demonstrated in pionless EFT. Finally, I examine power counting in chiral EFT and discuss the consistency of Weinberg's power counting. |
| Neural-network quantum Monte Carlo for atomic nuclei | |
| Dozent/Speaker: | Yilong Yang (Peking University) |
| Termin/Date: | Do. 11.07.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Solving quantum many-body problems is a common challenge in different fields of physics. Neural networks, trained with quantum Monte Carlo techniques, have proven to be a powerful tool for solving many-electron systems, while it is still quite challenging for atomic nuclei because of the complicated nuclear force.
In this talk, I will introduce our recent developments in utilizing neural networks in variational and diffusion Monte Carlo calculations of light nuclei. I will show that accurate solutions can be obtained for the ground states of few- and many-body nuclei, thanks to the strong expressive power of neural networks. |
| Recent Results for Nucleon Form Factors from Lattice | |
| Dozent/Speaker: | Dr. Dalibor Djukanovic (Helmholtz Institute Mainz) |
| Termin/Date: | Do. 04.07.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | I will show the most recent results for the nucleon form factors from the Mainz lattice QCD group. That includes results for the electromagnetic form factors of proton and neutron and the sigma term of the nucleon, with a discussion of the total error budget concerning statistical and systematic errors. |
| Nuclear Lattice Simulations and Parametric Matrix Models | |
| Dozent/Speaker: | Prof. Dr. Dean J Lee (Michigan State University) |
| Termin/Date: | Do. 27.06.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
During the first half of the talk, I review recent progress using nuclear lattice effective
theory. The topics include a many-body approach called wavefunction matching,
clustering and intrinsic shapes in light nuclei, spin and density correlations in neutron
matter, and signatures of exotic superfluidity.
In the second half, I give an introduction to a new machine learning approach called parametric matrix models, which uses the the matrix equations of quantum physics. I discuss several applications to scientific computing as well as more general machine learning applications. |
| Nucleon-nucleon scattering in chiral effective field theory with several cutoffs | |
| Dozent/Speaker: | Fabian Stollmann (RUB) |
| Termin/Date: | Mi. 06.06.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
The concept of effective field theory has great success in the description of nuclear physics. Based on the pioneering work by Weinberg, a chiral effective field theory of nucleon- nucleon interaction has been steadily developed. Nevertheless, the renormalization of this effective field theory and its consistency with a given power counting scheme is still part of controversial discussions.
In this seminar I will calculate the phase shifts in the 1S0 - and 3P0-channel at leading order with two cutoffs. In the 1S0 - channel I discuss issues of renormalization in the case of two cutoffs. The coupling constants are used to fit the phase shifts with experimental data. Doing so for multiple combinations of the cutoffs, one can make a renormalization group analysis and derive functions C(Λ1, Λ2) and C2(Λ1, Λ2). This allows to determine a range of cutoffs where the coupling constants are insensitive to a change. |
| Calculation of the beta-function in massive YM theory | |
| Dozent/Speaker: | Henri Paul Huesmann (RUB) |
| Termin/Date: | Mi. 29.05.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
In this seminar I discuss the asymptotic freedom of massive SU(2) Yang-Mills fields: Firstly for an effective field theory, where I added a globally invariant mass term to the most general Lagrangian that is invariant under local gauge transformations, secondly for a model that consists of the standard locally gauge-invariant Yang-Mills part and a globally invariant mass term of vector bosons.
The reason why this is of interest is that introducing massive gluons could cure the strong CP problem of Quantum Chromodynamics without having to introduce new particles. Whilst I cannot draw a clear conclusion for the first model, on the other hand I found that for the second model the bare coupling vanishes for large values of the cutoff, which indicates asymptotic freedom. The obtained results should be considered as a hint that a more comprehensive study might be worth of effort. |
| Calculation of the Vacuum Energy in an Effective Field Theory | |
| Dozent/Speaker: | Lennart Neuhaus (RUB) |
| Termin/Date: | Mi. 22.05.2024, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | The quantization of general relativity is possible in the framework of effective field theories. In my master thesis I demonstrate that by a consistency condition one is able to uniquely fix the cosmological constant order-by-order in loop expansion. This value of the cosmological constant cancels exactly the radiative contributions to the mass of the graviton, in agreement with a so called graviton low-energy theorem and corresponding Ward identity. The calculations are carried out for a model of a massive scalar field with linear and cubic interaction terms at two-loop order. Additionally I will shortly present the calculation of three-loop Feynman integrals. The general goal in two- and three-loop calculations will be to express loop integrals in a closed form depending on Gamma and hypergeometric functions. In this regard I will present mathematical tools that are of great help when solving higher order Feynman diagrams such as the Mellin-Barnes parameterization and the integration by parts method. |
| The status of neutrino masses | |
| Dozent/Speaker: | Sebastian Tanzius (TPII RUB) |
| Termin/Date: | Do. 26.10.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Neutrinos are the second most common particle in the universe, however the nature and the values of their extremely small masses remain a puzzle.
Direct measurement of the neutrino mass is technically very challenging and only an upper bound is obtained so far. On the other side, experimentally measured neutrino flavor oscillations demonstrate that at least some neutrinos must have nonzero masses. The theoretical description of neutrino mass effects is nontrivial either. The original formulation of the Standard Model assumed massless neutrinos which turned out to not be sufficient to describe observed neutrino properties. In this talk I will try to illuminate the quest to find the values of neutrino masses, as well as the changes in the Standard Model necessary to account for them. I will present an overview of the theoretical underpinnings of the Majorana fermion, neutrino oscillations, the see-saw mechanism and the current state-of-the-art mass determination experiments like KATRIN in Karlsruhe. |
| Few-nucleon scattering in NLO Pionless Effective Field Theory: n-d, n-3H, n-3He, and n-4He elastic scattering | |
| Dozent/Speaker: | Prof. Dr. Martin Schäfer (Nuclear Physics Institute of the Czech Academy of Sciences, Rez-Prague) |
| Termin/Date: | WE. 27.09.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | Pionless effective field theory (EFT)represents a convenient tool which allows to describe low energy properties of nuclear interaction. So far, perturbative inclusion of higher orders of this theory have been tested only in A<=3 nuclear systems. Up to three-body level, it has been shown that considering sub-leading terms systematically improves its predictive power. In my contribution, I will show how a few-body approach based on the Stochastic Variational Method with a correlated Gaussian basis and a harmonic oscillator trap, enables to study nuclear systems with A > 3. In particular, I will present the microscopic predictions of s-wave low-momentum n-d, n-3H, n-3He, and n-4He elastic scattering within perturbative next-to-leading order pionless EFT. The corresponding results will be compared to available experimental data. |
| Vector mesons in chiral perturbation theory | |
| Dozent/Speaker: | Prof. Dr. Tae-Sun Park (Institute for Basic Science, Daejeon, South Korea) |
| Termin/Date: | WE. 09.08.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | Vector mesons (VMs) have historically played a significant role as major building blocks in nuclear physics. However, with the advent of chiral perturbation theory (ChPT), their functions have been replaced by low-energy constants associated with pion and nucleon operators. Consequently, VMs have been nearly forgotten. |
| Wetterich equation in zero-dimensional quantum field theory | |
| Dozent/Speaker: | Maximilian Buthenhoff (RUB) |
| Termin/Date: | Mr. 05.07.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
For a quantum field theory (QFT) we need three ingredients: some kind of space (manifold with metric), some collection of fields that are defined on the manifold and an action that describes the dynamics of and interaction between the fields. A theory is called zero-dimensional if the space we consider is zero-dimensional, e.g. it consists just of a point. In QFT we are interested in objects (correlation functions) that are encoded as "path integrals". For non-trivial quantum field theories the calculation of these kind of integrals is very hard. The functional renormalization group (FRG) approach offers with the discovery of the Wetterich equation a new possibility to calculate these correlation functions.
In this talk I will give an introduction to the idea and usage of the Wetterich equation in zero-dimensional QFTs. I choose to discuss zero-dimensional QFTs because results we obtain are easy to verify (since the "path integrals" are just ordinary integrals over real space). The talk starts with basic definitions and a derivation of the Wetterich equation. In the main part of the talk an approach for solving the Wetterich flow equation for a scalar O(4) model is presented that transforms the equation into a fluid dynamical conservation law. This then offers a fluid-dynamical interpretation of the quantities occuring in the equation. The results are discussed and references of books/publications are given for further reading. The presentation is addressed to students. |
| Relativistic spatial distribution of charge and magnetization | |
| Dozent/Speaker: | Prof. Dr. Cedric Lorce (CPHT ‐ Ecole polytechnique, France) |
| Termin/Date: | Do. 22.06.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
We review the notion of spatial distribution in quantum field theory and present the phase-space approach. We apply this formalism to the electromagnetic current and study the frame dependence of the charge distributions.
In particular, we explain how Breit frame distributions are related to light-front (or infinite-momentum frame) distributions. Finally, we discuss recent results on magnetization and polarization. |
| Dark Matter Candidates and Searches | |
| Dozent/Speaker: | Andrii Kozytskyi (RUB) |
| Termin/Date: | Fr. 24.05.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Although it is universally agreed that the matter component of the Universe
consists for the most part of invisible, purely gravitationally interacting Dark
Matter, its composition remains a topic of great mystery and debate in theoretical
and experimental physics; it is perhaps the most important open question
on the confluence of nuclear physics and astrophysics, and has become a dauntingly
broad field of research. Attempts to solve the great mystery range from
very pragmatic minimal-assumption models to entirely novel approaches to the
whole of theoretical physics as we know it.
This presentation aims to give the audience an overview of the history of scientific understanding of the necessity of Dark Matter, relay some of the arguments regarding our current understanding of its probably composition, and attempt to outline the scope and complexity of the various theories attempting to solve the Dark Matter problem by categorizing them according to common assumptions and features. |
| Probing the Effect of Power-Law Divergences on Asymptotic Freedom in Massive Yang-Mills Theories at One-Loop Order | |
| Dozent/Speaker: | Lasse Ebener (RUB) |
| Termin/Date: | Fr. 14.04.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | Massive Yang-Mills theory, even though not renormalizable in the traditional sense, is renormalizable in the context of EFT. We study the effect of power-law divergences on asymptotic freedom at one-loop order in the EFT of massive SU(2) Yang-Mills theory. We employ a spontaneously broken SU(2) Yang-Mills theory with the mass m of the scalar boson as regulator for power-law divergences. In the limit where m is taken to infinity decoupling occurs and pure massive Yang-Mills theory is recovered, where possible power-law divergences are regulated by m. The coupling constant g is found not to receive any contributions due to power-law divergences at this level of the loop expansion. |
| Local spatial densities in light hadrons | |
| Dozent/Speaker: | Nils Lange (RUB) |
| Termin/Date: | We. 15.03.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
The aim of this talk is to provide an overview over the topic of local spatial densities in light hadrons and the recent developments regarding the relation between the radius and the form factor of a quantum system.
The central problem of this topic is the question of how to properly dene a classical quantity as the radius within the framework of relativistic quantum physics, since only the form factor is accessible through experimental data. First, the traditonal interpretation of the charge density distribution as the Fourier trans- form of the electric form factor is introduced. What follows is an overview of why this leads to ambiguities for systems whose intrinsic size is of the same order as their Compton- wavelength, and why this deniton is not suitable for light hadrons. Next, an approximate expression for the charge density distribution in the static limit by R.L. Jae in 2020 is presented. In 2022, Epelbaum et al. found an unambigous deniton of the charge density without making any approximations. The interpretation of this result is discussed and a one-dimensional example is presented for demonstration purposes. Furthermore, a geometric interpretation is established. Finally, a brief review of generalizations of the new denition for systems with nonvan- ishing spin and gravitational form factors is given. |
| Large-N limits for nuclear effective field theories | |
| Dozent/Speaker: | Dr. Thomas Richardson (Uni Mainz) |
| Termin/Date: | Do. 09.03.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/167 |
| Übersicht/Abstract: | The effective field theory (EFT) paradigm has undoubtedly reshaped nuclear physics in the last thirty years. While an EFT has the appeal of being model-independent, the operators in an EFT also appear with a a priori undetermined low energy coefficients (LECs). In the case of strongly coupled systems relevant for nuclear physics, these LECs must be determined either from experiment or by matching to lattice QCD calculations. In many cases neither option is yet viable; therefore, constraints from other means are necessary. The spin-flavor symmetry of baryons in the large-Nc limit of QCD, Nc being the number of colors, provides a tool to establish hierarchies of the LECs in the EFT. We discuss examples of these constraints relevant for electroweak currents, neutrinoless double beta decay, and dark matter direct detection. Lastly, we also consider other possible large-N limits that may be useful in nuclear EFTs. |
| Higgs Boson: Discovery and Outlook | |
| Dozent/Speaker: | Alexander Schumann (RUB) |
| Termin/Date: | Do. 24.02.2023, 14:15 - 16:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
I will give an overview of the topic of the Higgs Boson. The Higgs Boson was first mentioned by Peter Higgs in 1964 and is the only known fundamental scalar boson.
The Higgs Boson is the exchange particle of the Higgs field and according to theory gives mass to particles. The history of the Higgs Boson began in 1960 when the spontaneous symmetry breaking was discovered by Yoichiro Nambu. This caused a problem that infinite vacuum energies would be possible. To avoid this, the Goldstone boson was first introduced, but later replaced by the Higgs boson, which was later used by Weinberg in the unification of electromagnetic and weak interaction. The detection of the Higgs boson could not be done directly, but only via decay products. For this, protons are brought to collision and the invariant mass is calculated. After the discovery of the Higgs boson, the existence of the Higgs boson was consolidated by further measurements. Nevertheless, further questions around the boson remain open, whose research will be very time-intensive. Nevertheless, the Higgs boson is an essential particle of the universe. |
| Introduction to the Standard Model of Particle Physics | |
| Dozent/Speaker: | Fabian Stollmann (RUB) |
| Termin/Date: | Do. 01.02.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | I will give an overview of the Standard Model of particle physics and its basic properties. The Standard Model describes the fundamental particles that make up the matter in the universe and their interactions. First, there are the quarks and leptons that are the indivisible building blocks of matter. Furthermore, the Standard Model incorporates the force carrier bosons. These force carriers mediate the three fundamental forces: the electromagnetic, the weak nuclear and the strong nuclear force. Additionally, the Higgs Boson is included in the Standard Model. It gives rise to the mass of particles due to the Higgs mechanism. The Standard Model has been tested extensively and is very successful in explaining various phenomena. Although it makes accurate predictions, it is not a complete theory. It does not include a description of gravity or dark matter, and it fails to account for the non-zero mass of the neutrinos. Nevertheless, the Standard Model is the most widely accepted theory of particle physics and describes a lot of phenomena. |
| Bayesian Estimation of the Truncation Errors in the Chiral Effective Field Theory for Nucleon-Nucleon Scattering | |
| Dozent/Speaker: | Dominik Hillenkötter (RUB) |
| Termin/Date: | Do. 15.12.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | I will show the calculation of the low energy coefficients up to next-to-next-to-next-to-leading-order (N3LO) in the chiral perturbation theory for Nucleon-Nucleon scattering. This is done by by fitting the Lippmann Schwinger equation in the partial wave basis to scattering data from the Nijmegen Group. It is important to make reliable estimations of the uncertainties of the nucleoar forces introduced by chiral pertubation theroy. To estimate the relative importance of this order we are using a marginalizaion over the N3LO LECs. In contrast to the usual procedure, where one is comparing different orders to each other to estimate the chiral uncertainties. Here we use a new approch where the chiral uncertainties are estimated by marginalizing over higher-order contributions at the level of the interaction, without the use of any assumption regarding the size of the expansion parameter. |
| Hadronic spectra and exotic hadrons | |
| Dozent/Speaker: | Michael Abolnikov (RUB) |
| Termin/Date: | Do. 20.10.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | I will give an overview over exotic hadrons and related theoretical methods for classification and prediction of such states. The particular focus will lie on hadronic molecules. Hadrons are called exotic if they do not consist of two or three valence quarks. In order to fit exotic states in the overall picture of hadron physics, I will start with a brief historical review of ordinary states. It is already possible to obtain reasonable approximations for spectra of ordinary heavy quarkonia by considering the analogy to positronium, which is again analogous to the well known hydrogen atom. However, such a purely quantum mechanical framework has its limits because it cannot describe highly excited states located near some hadronic thresholds or account for decays. Thus, effective field theories are required to treat ordinary as well es exotic states in a more elaborate way. Hadronic molecules are regarded as pairs of weakly bound hadron-hadron states. Due to their low binding energy, they are especially well-suited to apply effective field theories, since the binding momentum is a natural soft scale in this case. Employing heavy quark spin symmetry allows to predict spin partner states of hadronic molecules, which can be experimentally tested. Different methods how to discriminate hadronic molecules from other multiquark configurations are discussed. |
| Naturalness as a Guiding Principle | |
| Dozent/Speaker: | Enno Fischer (Philosophy Department) |
| Termin/Date: | Do. 06.10.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | The naturalness principle demands that a theory should not involve independent parameters that are finely tuned. This principle was employed heavily over the last 40 years by theoretical physicists as a guideline for developing theories of beyond the Standard Model physics (BSM). But 10 years after the discovery of the Higgs boson, experiments at the Large Hadron Collider (LHC) have not found conclusive signs for new physics. As a consequence, the significance of naturalness arguments has been questioned and it has been suggested that high-energy physics may have reached the "dawn of the post-naturalness era." In this talk, I will address the naturalness principle from a philosophical perspective. First, I will introduce the naturalness problem of the Higgs. I will provide an overview of a range of definitions of naturalness that have been employed by particle physicists and discuss the conceptual relations between the definitions. I will also address the role that naturalness has played as a motivation for developing BSM theories and conclude the talk with some general lessons about guiding principles in physics. |
| Asymptotic safety and Einstein Quantum Gravity | |
| Dozent/Speaker: | Lennart Neuhaus (RUB) |
| Termin/Date: | Do. 22.09.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: |
Quantum gravity is perturbatively non-renormalizable, as we can see by dimensional analysis in natural units in which Newton's gravitational constant, serving as a coupling constant in the underlying Lagrangian of general relativity, has negative mass dimension.
The renormalization group gives a framework in which a theory can be analyzed in terms of its renormalizablity. Parameters of the theory undergo so called renormalization group transformations, where each iteration changes the scale of said parameters. Starting at the microscopic scale, the iterations induce a "coarse graining" resulting in corresponding effective theories describing the theory at a macroscopic level. Each iteration process traces out a trajectory in theory space, where the coordinates are given as the coupling constants of the underlying Lagrangian. A theory is now renormalizable, if the trajectory in theory space approaches a fixed point. A theory is called asymptotically safe, if it approaches a so called Non-Gaussian fixed point. In this presentation I will showcase the analysis of quantum gravity in the framework of the renormalization group and show that it approaches a Non-Gaussian fixed point in theory space. This predicts a non-perturbatively renormalizable theory of quantum gravity called Quantum Einstein Gravity. |
| Current status and future prospects on experimental study of three-nucleon forces | |
| Dozent/Speaker: | Prof. Dr. Kimiko Sekiguchi (Tohoku University, Japan) |
| Termin/Date: | Mo. 19.09.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/167 |
| Übersicht/Abstract: |
Understanding the strong nuclear force is of fundamental importance to decipher the natural way of building matter in the Universe. Since Yukawa's meson theory, the nuclear force had been formulated as two-nucleon interactions.
In the last two decades, the importance of three-nucleon forces (3NFs) that appear when more than two nucleons interact have been indicated in various nuclear phenomena. With the aim of exploring the 3NFs, experimental programs of three and four-nucleon scattering using the polarized beam and target systems are in progress at RIKEN, RCNP, and CYRIC in Japan. In the seminar, I will present current status and future prospects on experimental study of 3NFs. |
| Calculation of radiative corrections of Nucleon gravitational Form Factors in Chiral Effective Field Theory | |
| Dozent/Speaker: | Philpp Beißner (RUB) |
| Termin/Date: | Do. 15.09.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | Chiral Effective Field Theory is a powerful tool to investigate the properties of nucleons and other subatomic particles. In this talk, the Lagrangian for the interaction between nucleons and photons is investigated. The EMT of this Lagrangian is calculated and then further used to calculate the one-loop structure and the nucleon gravitational form factors. Also, the soft photon emission in connection to the scattering amplitude is discussed. |
| Nuclear Lattice Effective Field Theory for Light and Medium-Mass Nuclei | |
| Dozent/Speaker: | Prof. Dr. Serdar Elhatisari (Gaziantep University, Turkey) |
| Termin/Date: | Mi. 10.08.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | I will give an overview over exotic hadrons and related theoretical methods for classification and prediction of such states. The particular focus will lie on hadronic molecules. Hadrons are called exotic if they do not consist of two or three valence quarks. In order to fit exotic states in the overall picture of hadron physics, I will start with a brief historical review of ordinary states. It is already possible to obtain reasonable approximations for spectra of ordinary heavy quarkonia by considering the analogy to positronium, which is again analogous to the well known hydrogen atom. However, such a purely quantum mechanical framework has its limits because it cannot describe highly excited states located near some hadronic thresholds or account for decays. Thus, effective field theories are required to treat ordinary as well es exotic states in a more elaborate way. Hadronic molecules are regarded as pairs of weakly bound hadron-hadron states. Due to their low binding energy, they are especially well-suited to apply effective field theories, since the binding momentum is a natural soft scale in this case. Employing heavy quark spin symmetry allows to predict spin partner states of hadronic molecules, which can be experimentally tested. Different methods how to discriminate hadronic molecules from other multiquark configurations are discussed. |
| Introduction to the Standard Model of particle physics and its shortcomings | |
| Dozent/Speaker: | Felix Kruse (TP2, RUB) |
| Termin/Date: | Do. 23.06.2022, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | In my talk 'Introduction to the Standard Model of particle physics and its shortcomings' I am going to give an overview over the fundamental forces and elementary particles of nature. We will continue with symmetries that are given in the standard model and introduce QCD and Electroweak theory. Lastly we will focus on some successes of the standard model, as well as its drawbacks. My talk is directed at students who have some knowledge of QFT. |
| Probing the Effect of Power-Law Divergences on Asymptotic Freedom in Massive Yang-Mills Theories at One-Loop Order | |
| Dozent/Speaker: | Lasse Ebener (RUB) |
| Termin/Date: | Fr. 14.04.2023, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | Massive Yang-Mills theory, even though not renormalizable in the traditional sense, is renormalizable in the context of EFT. We study the effect of power-law divergences on asymptotic freedom at one-loop order in the EFT of massive SU(2) Yang-Mills theory. We employ a spontaneously broken SU(2) Yang-Mills theory with the mass m of the scalar boson as regulator for power-law divergences. In the limit where m is taken to infinity decoupling occurs and pure massive Yang-Mills theory is recovered, where possible power-law divergences are regulated by m. The coupling constant g is found not to receive any contributions due to power-law divergences at this level of the loop expansion. |
| Triangle Singularities and their Manifestations | |
| Dozent/Speaker: | John M. Diagne-Erdmann (TP2, RUB) will talk about |
| Termin/Date: | Do. 09.12.2021, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | The Color confinement of quantum chromodynamics manifests itself in the experimentally observable spectrum of hadrons. Due to the large technological progress in the last decades lots of new hadron resonant structures were discovered. Resonances, bound or virtual states show up as poles in the scattering amplitude, but there are also kinematic singularities which produce peaks in the invariant mass distributions as well, when the intermediate particles can go on-shell. Such singularities are for example two-body threshold cusps and triangle singularities. This seminar talk briefly reports on the triangle singularity mechanism and how it manifests in observable. |
| Dozent/Speaker: | Sven Heihoff (TP2, RUB) |
| Termin/Date: | Do. 04.11.2021, 16:15 - 17:45 |
| Ort/Location: | NB 6/173 |
| Übersicht/Abstract: | As recent measurements from experiments such as Xenon1T further constrain the idea for Dark Matter, the theoretical search for an extension to the Standard Model (SM) which leads to small cross-sections for Dark Matter interactions, intensifies. In this talk an effective field theory extension of the SM, i.e. introducing a new field, which interacts with fields of the SM at a scale above the electroweak scale is presented. The extension contains all operators up to and including mass dimension 6 and in front of each operator a unique Wilson coefficient takes place. With this model, nuclear observables such as transition probabilities or event rates for common direct detection experiments are derived. This derivation includes renormalization group effects as well as non-pertubative matching and is based on the packages "DirectDM" from Bishara et al. and "DMFormfactor" from Haxton et al. Thanks to a symbolic computation, these observables are directly dependent from the high scale Wilson coefficients, easing the search for unexpected cancellations and thus small observables. As an intermediate presentation of a master thesis project, this talk includes a detailed method discussion and feedback about the work in progress is highly appreciated. |