News on Medium-Mass Open-Shell Nuclei

May 2022

R. Roth

In an international collaboration with researchers from France and other countries we have published two papers as part of a three-paper series on new many-body methods for open-shell medium-mass nuclei using our family of chiral NN+3N interactions up to N3LO. We use a new multi-reference formulation of many-body perturbation theory as well as the in-medium NCSM, which provides a comprehensive set of benchmark result. This work focuses on the neon isotopic chain, but both methods hold great potential for broad applications in the medium mass-regime. Moreover the result highlight the predictive power of the chiral interactions we have developed. Have a look at the papers here and here or in the publications section.

Back to University

March 2022

R. Roth

The summer semester 2022 is about to start and we are offering the Computational Physics lecture live, interactive, and in-person in the Uhrturm lecture hall. All the exercise classes will also take place in-person. You will find all the relevant information on the web page of the lecture. On top of this, our group is running two advanced lab couses (F-Praktikum) using the TURM(X) Observatory... one on photometry of exoplanet transits and short-period variable stars and a second one on solar physics and the observation of the solar atmosphere. Check out the web pages of the TURM Observatory for more details.

TU News Article on the TURM Observatory

September 2021

R. Roth

The TU has published a nice news article on the TURM Observatory and our activities. Have a look at the main TU Darmstadt website. Some of our astro images have also been posted on the Instagram channel of the University.

LENPIC Paper on Applications of SMS Interactions

June 2021

R. Roth

A new paper of the LENPIC collaboration on a broad range of many-body calculations using the new semilocal momentum-space (SMS) interactions with consistent NN and 3N forces up to N2LO has appeared in Phys. Rev. C and was selected as an Editors' suggestions. In addition to a wide range of results for few-body and p-shell nuclei, it also features a detailed discussion on Bayesian uncertainty quantification for different obervables. Have a look at the paper here or in the publications section.

Advanced Lab Course on Solar Physics

April 2021

R. Roth

Starting this summer, we offer a new advanced lab course (Fortgeschrittenenpraktikum) on the "Physics of the Solar Atmosphere" -- our second one. Using the different telescopes of the TURM Observatory, the students oberve the sun in different wavelength windows, including narrowband observations tuned on specific atomic transitions. In addition to the study of atmospheric features, like sun spots and prominences, the students measure the limb darkening and the differential rotation of the sun. Due to the current restrictions at the TU, the lab course will be offered in a remote/digital format, i.e., the students operate the observatory from their computer at home. More information on our solar observations at TURM web page.

Precision Study of Magnetic Dipole Observables in Lithium-6

March 2021

R. Roth

In a new publication in Physical Review Letters we present a joint experiment and theory work on magnetic dipole observables in Lithium-6. Both, the measurement at the S-DALINAC and the ab initio NCSM calculations aim for a much improved precision for determining the M1 transition strength between the excited 0+ state and the ground state. For the ab initio calculation this implies the use of two-body corrections to the M1 operator resulting from chiral effective field theory as well as a consistent treatment of this operator throughout the calculation. We find a remarkable agreement with experiment. You can find more information in the news piece at the TU Darmstadt web page.

Remote Summer School at the Galileo Galilei Institute in Florence

March 2021

R. Roth

I was happy to be one of the lecturers at this years school on "Frontiers in Nuclear and Hadronic Physics" (FNHP2021) at the Galileo Galilei Institute in Florence, together with a number of great colleagues from the field of threoretical nuclear physics. Also this teaching activity was affected by the pandemic and had to take place as a remote event. Nevertheless, it was a great experience and there were many lively discussion with the students. As benefit of this format, the recordings of all the lectures are available via the Youtube channel of the Galileo Galilei Institute. You can find the slides of my lectures as well as the links to the Youtube videos on this page.

Bachelor Theses... Remote

February 2021

R. Roth

The winter semester is coming to an end - it was the second semester of digital teaching/learning and home-office for the group. This is also true for the students that joined the group for their Bachelor thesis project. Over the past year we had a large number of students in the group that all did an excellent job with their thesis research under difficult conditions. Some of them never had a chance to physically work at the institute and enjoy the team in person - I hope we can make up for this in the future. A big thanks and congratulations to all of you: Paul Christians, Jonas Winter, Lisa Wagner, Cedric Wenz, Daniel Kromm, and Katharina Schröder... and welcome to all of the new students!

Athene Sonderpreis "Digitale Lehre" 2020

November 2020

R. Roth

The Athene Sonderpreis "Digitale Lehre" 2020 was awarded to Franco Laeri and Robert Roth for establishing the TURM Observatory at the Department of Physics. We are very happy about this award and are motivated to push forward with this project... there is more to come. For more information on the Athene awards see the TU news piece. For more information on the TURM Observatory and our activities visit turm.physik.tu-darmstadt.de.

Theoretische Physik IV... Digital Lecture

October 2020

R. Roth

The winter semester 2020/21 will be the second digital semester at the TU. We are offering the statistical mechanics lecture, a.k.a. Theo. Physik IV, as an asynchronous digital lecture. There will be prerecoded videos on the individual sections of the lecture plus a weekly discussion session via Zoom. Also the exercise classes will be offered via Zoom. Definitely a new experience for all of us. You will find all the relevant information on the web page of the lecture.

TURM Observatory Website... Now Live

September 2020

R. Roth

Finally, the web site for the TURM Observatory is online! It is only the start and we expect much more material to appear there over the coming months. Already now you can find lots of information on our instrumentation at the TURM and TURMX setups, as well as images and the status information. Visit us at: turm.physik.tu-darmstadt.de.

Family of Chiral Interactions for Accurate Nuclear Structure Studies

August 2020

R. Roth

Our latest paper on a "Family of Chiral Two- plus Three-Nucleon Interactions for Accurate Nuclear Structure Studies" has appeared in Physics Letters B. This is a real milestone for us: For the first time we have a family of chiral interactions from LO up to N3LO for three different cutoff values that reproduces experimental ground-state energies and charge radii at the same time over a wide mass range. For us, this will be a game changer for a range of nuclear structure applications... lots of work to do!

Review: Many-Body Perturbation Theories for Finite Nuclei

June 2020

R. Roth

We have published an extensive review article on "Many-Body Perturbation Theories for Finite Nuclei" together with Alexander Tichai and Thomas Duguet in Frontiers in Physics. This review provides a detailed introduction and discussion of different versions of many-body perturbation theory applied to finite nuclei. Definitely a good starting point if you want to learn about perturbation theory in the context of nuclear structure... and it's fully open access.

Advanced Lab Course on Photometry

May 2020

R. Roth

After a test phase during the winter 2019/20 the advanced lab course (Fortgeschrittenenpraktikum) on "Photometry in Astrophysics" has started regular operation in summer 2020. Due to the current restrictions at the TU, the lab course will be offered in a fully remote/digital format, i.e., you can do everything from your computer at home. You will perform remote observation of a short-period variable star and a transiting exoplanet using our TURMX telescope, located in Spain. More at this web page.

TURMX Observatory

August 2019

R. Roth

While waiting for the completion of the construction work at the Uhrturm in the heart of the downtown campus of TU Darmstadt, we have installed a telescope system at a very remote location in the Extremadura Region ins Spain. Hosted at the E-EyE Astronomical Complex, this observatory will provide perfect sky conditions for night-time observations and we will use for advanced lab courses and other teaching and student activities in the Physics Department. Stay tuned for more information...

Joint Experiment-Theory Letter on the Radii of Boron-Isotopes

May 2019

R. Roth

Another nice example of experiment-theory collaboration: Together with the group of Wilfried Nörtershäuser and several researchers from the US we have published a Physical Review Letter on the charge radii of Boron-10 and Boron-11... a combination of precision experiments and theories! Have a look at the TU Press Release.

Natural-Orbital Basis for the NCSM

March 2019

R. Roth

Our paper on a new kind of optimized single-particle basis for the use in the No-Core Shell Model and other many-body methods has jut appeared in Physical Review C and was selected as Editors' Suggestion.

New Paper on the Hypernuclear No-Core Shell Model

December 2017

R. Wirth

The No-Core Shell Model is a powerful many-body method for light nuclei. Our initial Letter, in which we presented the extension of the NCSM methodology to hypernuclei along with a first survey of light hypernuclei, omitted the details of the method and the steps needed to include hyperons into the calculation for brevity. We just submitted a longer paper to Physical Review C, which contains these missing details. There, we present the NCSM for hypernuclei in two formulations, giving the steps needed to set up a calculation. We also show precision calculations of ground- and excited-state energies of the four-body system, as well as a short survey of helium hypernuclei in the p shell.

Letter on Light Neutron-Rich Hypernuclei

October 2017

R. Wirth

Adding a hyperon to a nucleus changes the structure of the nucleus, e.g., by lowering the ground-state energy and creating new excited states. These changes can create stable hypernuclei with unbound nucleonic cores and hypernuclei may be able to bind more neutrons than their nucleonic analogs. We submitted a study of neutron-rich helium and lithium hypernuclei to Physics Letters B, which is the first time these hypernuclei have been addressed in a calculation with a similarity-transformed chiral Hamiltonian. The transformed Hamiltonian allows us to reliably extract hypernuclear ground-state energies. With these, we investigate whether the neutron drip line of the helium and lithium hyperisotopic chains is changed compared to the nucleonic analogs.

Physical Review Letter on the In-Medium No-Core Shell Model

April 2017

R. Wirth

Ab initio many-body methods have different strengths and weaknesses. The No-Core Shell Model (NCSM), for example, can handle odd-mass systems and excited states but is limited in particle number. Medium-mass methods like the In-Medium Similarity Renormalization Group (IM-SRG) can handle higher particle numbers but are restricted to ground-states of even nuclei. With this Physical Review Letter we present a hybrid of the two methods that has the merits of both: the In-Medium No-Core Shell Model (IM-NCSM). The IM-NCSM uses the IM-SRG to decouple a small NCSM model space from higher excitations, dramatically improving convergence of NCSM calculations. This way, the IM-NCSM enables access to excited states and electromagnetic observables of medium-mass nuclei. Check out the publication for more information.

hoch3 FORSCHEN - Pieces of Cosmic Puzzles

April 2017

R. Roth

Based on our recent back-to-back publications in Physics Review Letters on the tetraneutron and the hyperon puzzle in neutrons stars, the TU Darmstadt has produced a little news piece for our hoch3 FORSCHEN magazine entitled 'Pieces of Cosmic Puzzles'. You can download the english version of the complete issue here and the german version here.

Physical Review Letter on the Tetraneutron

October 2016

R. Roth

Simultaneously with our letter on hypernuclei a second letter on an equally exotic nuclear system appeared: the tetraneutron, i.e., a systems composed of 4 neutrons. In collaboration with researchers from Russia and the US we have explored the existence of a low-lying resonance in the tetraneutron and we have predicted its energy and lifetime using novel ab initio methods including continuum degrees of freedom. Our results for the resonance energy are remarkably close to a recent experimental claim by a group from RIKEN. We will certainly continue to study this elusive system, which provides a sensitive probe for the neutron-neutron interaction. Several groups within the SFB 1245, both theory and experiment, will hunt for further insights into these systems beyond the neutron dripline.

Physical Review Letter on Induced Hyperon-Nucleon-Nucleon Interactions

October 2016

R. Roth

Unitary transformations are a key component for accelerating convergence of many-body calculations in order to reliably compute observables. These transformations induce many-body terms that have to be included in the calculation. We worked out the Similarity Renormalization Group (SRG) transformation of hyperon-nucleon interactions at the three-body level and can now precisely compute binding and excitation energies of hypernuclei. The induced three-body terms are stronger than expected and their appearance links into a long-standing puzzle in the physics of neutron stars. Check out the publications section...

New Paper with LENPIC Collaboration

April 2016

R. Roth

With the LENPIC Collaboration we have published a new paper in Physical Review C that marks another step towards a systematic uncertainty quantification in ab initio calculations. Using a new generation of semi-local chiral two-nucleon interactions from leading order (LO) to next-to-next-to-next-to-next-to leading order (N4LO) we study the systematics of various few-body observables and quantify the theoretical uncertainties. In the next step we will extend these studies to nuclear structure observables in heavier systems and include consistent 3N interactions up to N3LO. Stay tuned...

Physics Letters B on Hartree-Fock Many-Body Perturbation Theory

March 2016

R. Roth

We have studied many-body perturbation theory (MBPT) as a tool for nuclear structure calculations for quite some time now. Its simplicity makes it very a very attractive alternative to more complicated and computationally demanding methods like coupled-cluster theory. However, the problem with MBPT is the order-by-order convergence of the perturbation series. In this Letter we explore the impact of the partitioning, i.e. the definition of the unperturbed basis, on the convergence. Using high-order MBPT we explicitly show that a Hartree-Fock basis leads to convergent ground-state energies so that low-order approximation are meaningful. Moreover, we show that third-order MBPT is in excellent agreement with the most advances coupled-cluster approximations up to Sn isotopes at the fraction of the computational cost.

Next-Generation Master's Students

March 2016

R. Roth

The next generation of Master's students are starting their research work in our group. Simon Dentinger is going to work on the In-Medium Similarity Renormalization Group for the ab initio description of medium-mass nuclei. He will focus on the treatment and impact of of normal-ordered three-body contributions. Laura Mertes has started a research project on precision calculation of electromagnetic observables in light nuclei. In a fist step she will focus on magnetic dipole observables including consistent SRG evolution and two-body currents. Soon Hans Spielvogel will start his research project on the inclusion of continuum degrees of freedom into the importance truncated no-core shell model via the Gamow basis. All of these projects are important building block of our future research program. It's going to be fun!

Rapid Communication on the Multi-Reference Normal-Ordering

March 2016

R. Roth

Normal-ordering of second-quantized operators with respect to a give reference state is at the heart of practically all ab initio methods for describing medium-mass nuclei. In the majority of cases, the normal-ordered Hamiltonian is truncated at the two-body level, defining the normal-ordered two-body approximation, which omits a part of the three-body interaction. This paper presents the first test and application of the multi-reference version of the normal-ordered two-body approximation in connection with the no-core shell model. Our benchmarks are critical for applications of this approximations in other many-body methods, e.g., the multi-reference in-medium similarity renormalization group for open-shell medium-mass nuclei.

Rapid Communication on the Importance-Truncated Shell Model

February 2016

R. Roth

We have been working on transferring the concept of the importance truncation, which we developed for the no-core shell model, to the traditional valence-space shell model. In this first paper on the importance truncated shell model, we also explore powerful extrapolation techniques based on the energy variance to increase the accuracy of the method. This is particularly exciting in connection with new developments on the derivation of effective valence-space interactions, from the im-medium SRG of coupled-cluster theory, which give access to multi-shell valence spaces that are too large to handle with conventional shell model technology.

Start of New Collaborative Research Center SFB 1245

January 2016

R. Roth

The first funding period of our new Collaborative Research Center SFB 1245 "Nuclei: From Fundamental Interactions to Structure and Stars" has started! This is a new and exciting project that builds on the strengths of the local groups in nuclear theory and experiment. You can find detailed information on the research goals at the website of the SFB 1245. The research activities of our group adress central parts of the SFB program, particularly in project A02 and A04. Let's start our work!

My Second Job as Head of the Department

October 2014

R. Roth

Starting in the Winter Semester 2014/15, I took over the position as the "Dekan" of the Department of Physics. This will mean a very busy schedule for the coming two years...

ECT* Workshop "From Few-Nucleon Forces to Many-Nucleon Structure"

June 2013

R. Roth

Our recent ECT* Workhop entitled "From Few-Nucleon Forces to Many-Nucleon Structure" was a great success. We had many stimulating discussions briding the communities of researchers working on chiral effective field theory for the construction of nuclear interactions and those developing and appying ab initio many-body techniques to predict nuclear structure and reaction observables. The talks of the workshop are available on-line at the workshop web site.

Phys. Rev. Lett. on Ab Initio Description of Oxygen Isotopes

June 2013

R. Roth

In a new Physical Review Letter we present the first parameter-free ab initio study of all even oxygen isotopes with chiral nucleon-nucleon and three-nucleon interactions, from the proton to the neutron drip lines. We employ three different ab initio many-body methods: the newly formulated Multi-Reference In-Medium SRG, the Importance Truncated NCSM, and Coupled Cluster Theory. We obtain an excellent reproduction of experimental ground-state energies with quantified uncertainties. This and the agreement between conceptually different many-body approaches and experiment highlights the predictive power of current chiral two- and three-nucleon interactions.

ECT* Workshop "From Few-Nucleon Forces to Many-Nucleon Structure"

February 2013

R. Roth

Together with Bruce Barrett and Rupert Machleidt we are organizing a one-week Workhop entitled "From Few-Nucleon Forces to Many-Nucleon Structure" starting on June 10, 2013 at the ECT* in Trento. The workshop will focus on the interplay of chiral effective field theory for the construction of nuclear interactions and ab initio many-body techniques using these interactions to predict nuclear structure and reaction observables. We aim to establish a continued exchange and feedback cycle between the two areas, promoting the use of QCD-based interactions for precise and predictive nuclear structure and reaction calculations. Have a look at the web site of the workshop.

Editors' Suggestion for our Phys. Rev. C Rapid Communication

February 2013

R. Roth

Our paper entitled "Ab Initio Study of Medium-Mass Nuclei with Explicit 3N Interactions" reporting on our recent coupled-cluster calculations has appeared as Rapid Communication in Phys. Rev. C 87, 021303(R) (2013). In addition the paper was featured as an "Editors' Suggestion" -- a small number of PRC papers that the editors and referees find of particular interest, importance, or clarity. We are very pleased with this distinction and take it as encouragement for our ongoing work on the ab initio description of medium-mass nuclei.

Official Opening of the Theory Center

January 2013

R. Roth

On January 16th our Theory Center was officially inaugurated by the President of the TU Darmstadt, Prof. Dr. H. J. Prömel, and the President of the Helmholtz Association, Prof. Dr. J. Mlyneck. After substantial renovation works funded by the TU Darmstadt, the building S2|11 now houses all theory groups of the IKP. The building offers four floors of office space plus a small lecture and seminar room. We are very grateful for the support of the University, providing us with this much-needed space. Have a look at the official press release.

Two Papers Appeared in Phys. Rev. C

December 2012

R. Roth

Two of our recent papers have appeared in Phys. Rev. C. The first one investigates the use of degenerate many-body perturbation theory up to high orders for the description of open-shell nuclei and excitation spectra utilizing Pade resummations. The second paper discusses two-nucleon overlaps and knockout reactions from 12-C in the context of the no-core shell model and has direct implications for experiments. Please check the Publications section.

New Paper: Ab Initio Study of Medium-Mass Nuclei with Explicit 3N Interactions

November 2012

R. Roth

We present, for the first time, ab initio calculations of medium-mass nuclei using explicit three-body interactions. Using coupled-cluster theory with three-body Hamiltonians we describe ground-state energies for nuclei as heavy as 56-Ni. We systematically address all truncations in the many-body framework and quantify the resulting uncertainties. Furthermore, we confirm the quality of the normal-ordering approximation of the three-body interaction by direct comparison. Our work sets a milestone for the ab initio description of medium-mass nuclei, which is a very active frontier in nuclear structure theory at present. Have a look at the preprint in the Publications section.

Structure of 16-C: Paper Appeared in Phys. Rev. C

October 2012

R. Roth

Our joint study of the spectroscopy of 16-C, combining new experiments on the lifetimes of the 2+ states, phenomenological shell model calculations, and ab initio No-Core Shell Model calculations, has appeared in Phys. Rev. C 86, 044329 (2012). It is a great example of how state-of-the-art nuclear structure theory and experiment can play together.

Two New Master Students and a Bachelor Student

October 2012

R. Roth

We welcome the next generation of Master and Bachelor students in our group: Stefan Schulz has started his research work towards the Master thesis on SRG-induced many-body interaction and their treatment. Alexander Tichai, the second new Master student, is working on advanced resummation methods for many-body perturbation theory. Our new Bachelor student, Philipp Isserstedt, is working on generalized harmonic oscillator bases in the context of the No-Core Shell Model. Have fun!

New Paper: Degenerate Perturbation Theory for Spectra of Open-Shell Nuclei

September 2012

R. Roth

We investigate the use of degenerate many-body perturbation theory up to very high order, typically up to 30th order, for the description of ground states and excitation spectra of closed and open shell nuclei. We demonstrate that the oerder-by-order perturbation series does not converge even for very soft SRG-evolved interactions. However, a resummation using Pade approximants gives results for ground state and excitation energies in very good agreement with exact no-core shell model calculations. Have a look at the preprint in the Publications section.

Phys. Rev. Lett. on Ab Initio Description for Medium-Mass Nuclei

August 2012

R. Roth

Our work on ab initio ground-state calculations for medium-mass nuclei based on chiral NN+3N interactions using coupled cluster theory and a normal-ordering approximation for including the three-nucleon interaction has appeared in Phys. Rev. Lett 109, 052501 (2012). Whereas most other approaches for this mass range rely on uncontrolled approximations and phenomenology for handling the 3N interaction, we demonstrate that the normal-ordering approximation is able to provide ground-state energies with an accuracy of about 1% in, e.g., the Calcium isotopic chain.

TNP++ Doctor... Number Five

July 2012

R. Roth

Dr. Bastian Erler is the fifth Doctor in the TNP++ family. Congratulations! His research work includes the development of a Hartree-Fock and RPA framework for the description of deformed nuclei including exact angular-momentum projections. With these tools he has investigated structure and collective response of alpha-nuclei in the sd-shell. This project is directly connected to recent experiments and we are now working with our experimental colleagues at the IKP to confront the theoretical results with experiment. Have a look at Bastian's thesis.

Four New Master Students

March 2012

R. Roth

We welcome our new generation of master students: Christina Stumpf, Eskendr Gebrerufael, Richard Trippel, and Roland Wirth. They will work on an array of nuclear structure topics, including the application of an importance-truncated shell model, the development of a multi-reference normal-ordering approach, a first RPA implementation with chiral 3N interactions, and the ab initio description of hypernuclei. This will be great fun!

Physics Letters B on Prediction of Low-Lying Isocalar Dipole Modes

February 2012

R. Roth

Our study of the systematics of low-lying isocalar dipole excitations in the Calcium isotopic chain using QRPA and SRPA has appeared in Phys. Lett. B 709, 270 (2012). It is a great example that very common nuclei still hold some surprises. The low-energy dipole response of nuclei is even more interesting and complicated than it was believed so far.

New Paper: Ab Initio Description for Medium-Mass Nuclei with Chiral NN+3N Interactions

December 2011

R. Roth

Complementing or recent letter on the first ab initio calculations with SRG-evolved chiral NN+3N interactions in the upper p-shell, we have now completed a study using the same chiral NN+3N interactions in a normal-ordering approximation for nuclei as heavy as 48-Ca. We benchmark the normal-ordering approximation of the 3N interaction in the IT-NCSM and apply it for the first time in coupled-cluster calculations for medium-mass nuclei in large model spaces. Have a look at the preprint in the Publications section.

New Paper: Low-Energy Dipole Strength in Calcium Isotopes

October 2011

R. Roth

Following our recent discovery of a collective low-energy isoscalar excitation in N=Z nuclei, we have now studied the interplay of this mode with other low-lying dipole excitations, e.g. the isovector Pygmy dipole mode, for varying number of neutrons throughout the Calcium isotopic chain. The study confirms the importance of the low-lying isoscalar dipole mode for a complete understanding of the low-energy dipole strength. You can find the preprint in the Publications section.

New Paper: Systematics of 2+ Excitations in the Carbon Chain

October 2011

R. Roth

In collaboration with Christian Forssen and Petr Navratil we have completed a study of the systematics of 2+ excited states for even Carbon isotopes from A=10 to 20, including spectroscopic obervables such as B(E2) strengths and quadrupole moments. These isotopes are a frontier and a challenge for ab initio nuclear structure methods, like the No-Core Shell Model (with and without Importance Truncation), and for present experiments alike... and they reveal a number of surprises! Have a look at the preprint in the Publications section.

Ab Initio Study of Proton Capture on 7-Be Published in Phys. Lett. B

September 2011

R. Roth

Our letter on the ab initio calculation of the astrophysical S-factor for the radiative proton-capture on 7-Be was published in Phys. Lett. B 704, 379 (2011). We are now looking into further applications of the IT-NCSM/RGM scheme for low-energy scattering and reactions.

Ab Initio Study with Chiral NN+3N Interactions Published in Phys. Rev. Lett.

August 2011

R. Roth

Our milestone study on ab initio nuclear structure calculations with chiral two- plus three-nucleon interactions in the upper p-shell was published in Phys. Rev. Lett. 107, 072501 (2011). We are now working on a follow-up paper with many more details and exciting results... stay tuned.

DFG Collaborative Research Centre 634 Funded until 2015

July 2011

R. Roth

The Deutsche Forschungsgemeinschaft (DFG) has approved the third funding period of our highly successful Collaborative Research Centre 634 "Nuclear Structure, Nuclear Astrophysics and Fundamental Experiments at Low Momentum Transfer at the S-DALINAC". Our group defines and carries out a significant part of the research program of the two theory projects D1 and D2. Have a look at the web-pages of the CRC 634.

First Ab Initio Calculation of Proton Capture on 7-Be

June 2011

R. Roth

In continuation of our successful collaboration with Petr Navratil (TRIUMF) and Sofia Quaglioni (LLNL) on the ab initio description of scattering and reactions of light nuclei, we have performed the first ab initio calculations of the astrophysical S-factor for proton capture on 7-Be. By combining the IT-NCSM with the Resonating Group Method (RGM) we gain access to this observable which plays a crucial role in understanding the pp-chain in our sun and the solar neutrino flux. Have a look at the preprint in the Publications section.

Paper on Quasiparticle RPA with Realistic Interactions Published in Phys. Rev. C

June 2011

R. Roth

Our paper on fully consistent Quasiparticle Random Phase calculations of the nuclear response with realistic interactions has been published in Phys. Rev. C 83, 064317 (2011). This work is the basis for several new studies with a direct link to the experimental program on collective excitations at the S-DALINAC and at GSI.

Ab Initio Spectroscopy with Chiral Two- plus Three-Nucleon Interactions

May 2011

R. Roth

In a groundbreaking effort we have developed a framework for ab initio nuclear structure calculations in the Importance Truncated NCSM using consistently SRG-transformed chiral two-nucleon (NN) plus three-nucleon (3N) Hamiltonians. Our work pushes the limits of state-of-the-art ab initio calculations with full 3N interactions to heavier nuclei and larger model spaces. In a first study we investigate nuclei up to 16-O and address the issue of SRG-induced 4N interactions. Have a look at the preprint in the Publications section.

Collaboration on No-Core Monte-Carlo Shell Model

May 2011

R. Roth

In collaboration with colleagues from Japan and China we have completed a first ab initio study using a no-core version of the Monte Carlo shell model. We discuss initial applications to the spectroscopy of Beryllium isotopes in a paper submitted to Phys. Rev. C. You'll find the manuscript in the Publications section.

Quasiparticle RPA with Realistic Interactions

April 2011

R. Roth

We have submitted a new paper with Heiko Hergert (MSU) as lead author on first fully consistent QRPA calculations of the nuclear response with realistic interactions. This extensive work is a milestone in our RPA developments which allows us to tackle open-shell nuclei throughout the nuclear chart. Together with our recent findings on the low-energy dipole response this opens exciting prospects for future studies. You'll find the paper in the Publications section.

Phys. Lett. B Published in Collaboration with Experiment

March 2011

R. Roth

In a successful collaboration with our colleagues from experiment we have analyzed the fine structure of the giant quadrupole resonance in 40-Ca through RPA and Second-RPA calculations with realistic nuclear interactions. The wavelet analysis of new high-resolution experimental data and of our theoretical response reveals a nice agreement of the scales already at the RPA level, which is a hint at Landau damping as a source of the fine structure. Have a look at Phys. Lett. B 698 (2011) 191.

Congratulations Dr. Anneke Günther

February 2011

R. Roth

Anneke Günther has sucessfully defended her thesis on "Nuclear Structure with Unitarily Transformed Two-Body plus Phenomenological Three-Body Interactions" and now is our fourth TNP++ Doctor. Congratulations! Her work marks our first step towards the incusion of realistic three-nucleon interactions in nuclear structure calculations.

Paper Published in the European Physical Journal A

January 2011

R. Roth

Our very recent paper on the collective low-energy isoscalar dipole excitations in N=Z nuclei, the so-called isospoin-fobidden dipole strength, has been published in Eur. Phys. J. A 47, 14 (2011). We will continue with this very exciting line of reasearch, stay tuned!

Four TNP++ Bachelors

December 2010

R. Roth

In the past months four Bachelor students have sucessfully completed their thesis work in the TNP++ Group. Two of them, Christina Stumpf and Roland Wirth, have been working on topics from nuclear structure theory and theo other two, Johannes Battenberg and Kim Oliver Hofmann, have been studying ultracold atomic gases. Congratulations to all of them!

Athene Teaching Award 2010

November 2010

R. Roth

The Carlo and Karin Giersch Foundation at the TU Darmstadt has awarded the departmental prize for teaching (Athene Fachbereichspreis für Gute Lehre) to Robert Roth for 'his achievements and his leading role in teaching Theoretical Physics'. The prize is shared with Prof. Thomas Walther and was awarded during the 'Tag der Lehre', the official announcement can be found here

Paper on Bosonic Rb-Atoms in Two-Color Superlattices Published in J. Phys. B

November 2010

R. Roth

Our paper on the phase diagram of ultracold gases of Rb-atoms in optical two-color lattices has appeared in J. Phys. B 43, 235301 (2010). It demonstrates a systematic ab-initio approach to the phase diagram using the experimental setup, characterized by the laser setup and the atomic species, as starting point for high-precision many-body calculations wihtin the density-matrix renormalization group (DMRG) approach. We highlight the effects of the harmonic trapping on the phase diagram and the presence of a Bose-glass phase.

New Paper: Isoscalar Low-Energy Dipole Collectivity

November 2010

R. Roth

We have submitted an exciting new study on the low-energy dipole response in nuclei. For the first time, we analyze in detail a collective isoscalar dipole excitation in N=Z nuclei, i.e., 16-O, 40-Ca, 56-Ni, and 100-Sn, which is related to the so-called forbidden E1 strength. This mode is yet another member of a family of dipole excitations below the giant dipole resonance -- the low-lying dipole strength, also for neutron-rich isotopes, is getting even more interesting. You'll find the paper in the Publications section.

Two Masters and a Three-Body Force

November 2010

R. Roth

Angelo Calci and Joachim Langhammer have completed their Master theses and started an exciting new research program within the group. They have developed the machinery for handling matrix elements of chiral three-nucleon interactions, for performing consistent SRG-transformations in three-body space, and for including full three-nucleon interactions into many-body calculations. A lot of important applications are waiting... and we are happy that Angelo and Joachim will stay with us for their PhD.

Bye-Bye Markus

October 2010

R. Roth

The first generation of TNP++ students is gone... Dr. Markus Hild, who joined us for a mini research project a long time ago has left the group after a successful career as Diploma and Doctoral student and finally as a Postdoc. He is now working for the GIP AG in Mainz and is developing Smart Grid technologies. All the new generation TNP++ members send their very best wishes for your future, Markus!

Lecture on 'Advanced Quantum Mechanics'

October 2010

R. Roth

The winter semester is about to start and after a sabbatical past summer we will be offering the course on 'Advanced Quantum Mechanics'. Moreover, we contribute to Doctoral Seminar on modern aspects of nuclear structure physics together with several colleagues from experimental and theoretical nuclear physics. Stay tuned for updates.

Two Papers Published in Phys. Rev. C

September 2010

R. Roth

Our two recent nuclear physics papers have appeared in Phys. Rev. C. The first of them discusses first ground-state calculation with phenomenological three-nucleon interactions and paves the way for upcoming studies with consistent SRG-transformed two- plus three-nucleon interactions from chiral EFT. The second paper results from a collaboration with Petr Navrátil and Sofia Quaglioni and presents first applications of the IT-NCSM/RGM framework for the description of nucleon-nucleon scattering observables for target nuclei as heavy as 16-O. You'll find the links in the Publications section.

Research Cluster "Nuclear and Radiation Science"

September 2010

R. Roth

The TU Darmstadt has officially established a Research Cluster "Nuclear and Radiation Science" following a proposal led by the IKP together with a number of partners in the Physics Department and across the TU. It is one of only five clusters that define the research profile of the TU Darmstadt. We are happy to participate in this collaborative effort. You will find more details on the new web-page of the Research Cluster.

Bye-Bye Felix

August 2010

R. Roth

After a successful time as Diploma and Doctoral student in our group Dr. Felix Schmitt - our second TNP++ Doctor - has set out to explore new horizons. He is now facing exciting new challenges at the DFS Deutsche Flugsicherung in Langen. All the very best for your future, Felix!

Excellence in Teaching Award 2010

July 2010

R. Roth

The Department of Physics at the TU Darmstadt has awarded the price for Excellence in Teaching 2010 to Prof. Dr. Robert Roth for various lectures in theoretical physics. I am very happy about this recognition and the whole group will try to keep up the good work for the coming lectures.

New Paper: Ab Initio Nucleon-Nucleus Scattering in the IT-NCSM/RGM

July 2010

R. Roth

In collaboration with Petr Navrátil and Sofia Quaglioni (LLNL) we have submitted a detailed paper on ab initio calculations for low-energy nucleon-nucleus scattering in the IT-NCSM/RGM framework. The combination of importance-truncated no-core shell model (IT-NCSM) for the description of the clusters' ground and excited states and the resonating group method (RGM) for the relative motion proves very powerful and opens new avenues, e.g., for ab initio calculations of reactions relevant in astrophysics. You'll find the paper in the Publications section.

New Paper: Ab Initio Phase Diagrams for Ultracold Bosons in Optical Superlattices

May 2010

R. Roth

We have submitted follow-up paper discussing the quantum phase diagrams of bosonic atoms in two-color superlattices as function of the experimental control parameters - the intensities of the lattice lasers. By combining band-structure calculations (to map the experimental system onto the Hubbard model) and density-matrix renormalization group (to solve the many-body problem) we present a rigorous ab-initio description and discuss the impact of experimental details, e.g., the presence of an additional harmonic confinement. You'll find the paper in the Publications section.

Phenomenological 3N interaction in connection with UCOM and SRG

May 2010

R. Roth

We have submitted a new paper marking our first step towards a full inclusion of three-body interactions into our many-body machinery. Using simple phenomenological three-nucleon interactions, we explore the effects on binding energies and charge radii throughout the nuclear chart and setup the technology to do the same with realistic 3N interactions. Have a look at the Publications section.

New Web Layout

May 2010

R. Roth

Markus Hild has revamped our web site with a beautiful new layout and numerous technical improvements. Not everything has been converted to the new layout yet... but we are working on it.

Ab Initio Scattering of Light Nuclei

April 2010

R. Roth

As a first major step towards the combination of ab initio nuclear structure and reaction calculations in the context of the importance truncated no-core shell model (IT-NCSM), a conference contribution to the FB19 conference has appeared in EPJ Web of Conferences 3, 01012 (2010). This is the first outcome of a project led by Petr Navrátil and Sofia Quaglioni.

Review Article in Prog. Part Nucl. Phys.

April 2010

R. Roth

Our review article on the Unitary Correlation Operator Method (UCOM) and the Similarity Renormalization Group (SRG) as a tool to construct soft nuclear interactions has appeared online in Prog. Part. Nucl. Phys. Please have a look at the Journal's Web Site.

New Bachelor students and Mini-Researchers

March 2010

R. Roth

We welcome three new Bachelor students and Mini-Researchers in our group. Two of them, Johannes Battenberg and Kim Oliver Hofmann, are continuing our work on the dynamical simulation of Bose gases in optical ring traps in collaboration with the experimentalists around Prof. Birkl. The third, Roland Wirth, is contributing to our research on Padé-resummed perturbation theory for nuclear structure.

New Papers

February 2010

Our paper on "Large-scale Second RPA calculations with finite-range interactions" has appeared in Phys. Rev. C 81, 024317 (2010). Moreover, an extensive review article on the Unitary Correlation Operator Method (UCOM) and the Similarity Renormalization Group (SRG) and their application in nuclear structure calculations was accepted for publication in Progress in Particle and Nuclear Physics. Have a look at the Publications section.

We have moved! - partly

January 2010

Part of the TNP++ group has moved to our new headquarters in building S2|11, Schlossgartenstr. 2. The rest of the group will follow this summer. This new location just across the road from the Institut für Kernphysik will become the IKP Theory Center and the home of all HIC for FAIR and EMMI theoreticians at the TU Darmstadt.

New Paper

January 2010

Our first 2010 paper has appeared! It's a Physics Letter on "Padé-resummed high-order perturbation theory for nuclear structure calculations". Have a look at Phys. Lett. B 683 (2010) 272 or in the Publications section.

December 2009

Just before Christmas our third TNP++ Doctor has sucessfully defended his thesis on the "Quantum Dynamics of Strongly Correlated Ultracold Bose Gases in Optical Lattices". Congratulations to Dr. Markus Hild! Now it's time to relax.

November 2009

Our letter on the treatment of the "Treatment of the Intrinsic Hamiltonian in Particle-Number Nonconserving Theories" has appeared in Phys. Lett. B 682 (2009) 27. Have a look!

November 2009

The TNP++ group proudly extends congratulations to Dr. Felix Schmitt. He defended his Doctoral thesis on "Ab-Initio Quantum Phase Diagrams of Ultracold Atomic Gases in Optical Lattices" successfully and now is our second TNP++ Doctor. All the best for you!

October 2009

Meanwhile, our two Bachelor students have completed their projects as well: Lutz Görgen has finished his thesis on the dynamics of Bose-Einstein condensates in one-dimensional ring traps and Nils Vogelmann his work on alternative strategies to extract UCOM correlators. Congratulations!

October 2009

In a new preprint we present first calculations of nuclear ground-state energies in many-body perturbation theory (MBPT) up to 30th order. We show that finite partial summations of the MBPT series typically diverge. However, through a resummation using Padé-approximants we obtain a very stable and highly accurate result. Have a look at our preprint.

October 2009

We have submitted a detailed discussion, including many technical aspects, of our Second RPA (SRPA) studies. This will serve as a baseline paper for many applications of SRPA, which we are working on right now. Have a look in the Publications section.

October 2009

The lectures of the winter semester 2009/10 have started and we are responsible for the Computational Physics course. Check out the information on the web pages accompanying this lecture.

September 2009

We are happy to welcome two new Master students in the TNP++ group: Angelo Calci and Joachim Langhammer are joining our team working on realistic QCD-based three-body forces for various nuclear structure applications. This is going to be exciting!

September 2009

At the same time we say good-bye to Heiko Hergert the most senior TNP++ group member who went to the group of Scott Bogner at NCSL/MSU for a postdoc. We wish you all the best for the future!

August 2009

And here comes number three! Our paper on the phase diagram of atomic Bose gases in two-color superlattices described in a systematic ab initio framework starting from a band-structure calculation and then solving the many-boson problem using the density-matrix renormalization group (DMRG) has just appeared in Phys. Rev. A 80, 023621 (2009).

August 2009

Two of our papers have just appeared in print: First our study on center-of-mass contaminations and diagnostics in configuration interaction and coupled-cluster calculations in Phys. Lett. B 679, 334 (2009). Then, a little later, our discussion of fully consistent Hartree-Fock-Bogoliubov calculations in the UCOM framework in Phys. Rev. C 80, 024312 (2009).

August 2009

We have submitted a remarkable new study on the treatment of the intrinsic kinetic energy in many-body calculations without particle-number conservation, most notably in pairing calculations in a Hartree-Fock-Bogoliubov scheme framework. There are some surprises - have a look at the preprint in the Publications section.

July 2009

Our ECT* Workshop entitled 'Linking Nuclei, Molecules, and Condensed Matter: Computational Quantum Many-Body Approaches' is over. It was a very stimulating and productive workshop with lots of important interactions among the participants from different fields of quantum many-body science (nuclear structure, condensed matter, and quantum chemistry). We will try to continue this fruitful inter-disciplinary exchange.

June 2009

Our big paper on the importance truncation in configuration interaction approaches, in particular the importance-truncated no-core shell model (IT-NCSM), with all technical aspects and a number of applications has appeared in Phys. Rev. C 79, 064324 (2009).

June 2009

We have completed a detailed analysis of the center-of-mass problem in different configuration interaction and coupled-cluster calculations. This work sheds new light on some recent claims about the absence of CM contaminations in coupled-cluster calculations. Have a look at the preprint in the Publications section.

May 2009

Our paper comparing ab-initio coupled-cluster and importance-truncated configuration interaction calculations has appeared in an extended version in Phys. Rev. C 79, 054325 (2009).

May 2009

We welcome (now officially) two new Bachelor students in our group. Nils Vogelmann is working on new schemes for the optimization of UCOM correlators and Lutz Görgen is studying the time evolution of quasi one-dimensional atomic Bose-Einstein condensates in circular traps in collaboration with the group of Gerhard Birkl.

April 2009

We have submitted a first paper on our applications of the density matrix renormalization group (DMRG) method for the exact description of atoms in optical lattices. We study the phase diagram of bosons in two-color superlattices in terms of simple experimental control parameters--the intensitites of the lasers generating the optical lattice. We show that all relevant quantum phases (superfluid, Mott-insualtor, quasi Bose-glass) are accessible by variation of the intensities alone. Have a look at the Publications section.

April 2009

The lectures of the summer semester 2009 have started. This time, our group is running the lecture on Quantum Mechanics and a theory seminar on Nuclear Structure and Nuclear Astrophysics. Have a look at the respective web-pages for more information.

April 2009

The TU Darmstadt has release a new issue of it's research magazine "forschen" with the title "Forschen in Quantenwelten". It contains more than 14 excellent articles for the general public written by researchers from the TU Darmstadt and GSI. The topical focus is on the physics program of FAIR and the broad range of activities at the TU Darmstadt geared towards the FAIR project. You can download a PDF file of the magazine from this site - our article is also available in the Publications section.

March 2009

We have completed a big paper on the importance-truncation scheme with a series of benchmarks and applications within the no-core shell model (NCSM). This new computational scheme extends the domain of the ab initio NCSM to much larger model spaces and heavier nuclei while preserving the power of full NCSM. You'll find the preprint in our Publications section.

February 2009

We have submitted a detailed paper on a first fully consistent study of pairing phenomena with UCOM interactions in the Hartree-Fock-Bogoliubov framework which is based on Heiko Hergert's work. More is to come... For now you can download the manuscript in the Publications section.

February 2009

The web-site for our ECT* Workshop 'Linking Nuclei, Molecules, and Condensed Matter: Computational Quantum Many-Body Approaches' which will take place from July 6 to 10, 2009 is online. Please have a look and feel free to contact us if you are interested in participating.

January 2009

Two new Doctoral students have joined the group. Helena Krutsch will start working on new applications of the no-core shell model to nuclei and ultracold atomic Fermi gases. Bastian Erler will extend our QRPA studies with realistic interactions towards exotic nuclei. We welcome both of them!

January 2009

Our letter on Second-RPA applications with realistic interactions was published in Phys. Lett. B. Moreover, we have submitted three contributions to the GSI Scientific Report 2008. Have a look at the Publications section.

December 2008

In the past months our three Bachelor students - Christoph Popa, Joachim Langhammer, and Florian Wagner - have completed their theses on different aspects of our nuclear structure theory program. Congratulations! You can have a look at their work in the Theses section. How about you? We are always looking for clever Masters and Doctoral students!

November 2008

The slides of my lecture in this year's Saturday Morning Physics program are available for download. Have a look at the Sat. Morning Phys. section.

November 2008

After a six-year period as Junior Professor concluded by another thorough review the University has awarded me tenure. I'm very happy about this decision and the opportunity to continue and intensify the work here.

August 2008

The ECT* in Trento has approved our proposal for a inter-disciplinary workshop entitled 'Linking Nuclei, Molecules, and Condensed Matter: Computational Quantum Many-Body Approaches' which will take place from July 6 to 10, 2009 at the ECT*. We organize this workshop jointly with Prof. J. Schnack (Univ. Bielefeld) and Prof. J. Richter (Univ. Magdeburg) with the aim to promote the exchange between experts on modern computational many-body methods from different fields ranging from nuclear physics, over condensed matter (spin systems and quantum gases), to quantum chemistry. More information soon...

July 2008

The joint proposal of the universities Darmstadt, Frankfurt, Gießen, and the Frankfurt Institute for Advanced Studies for a "Helmholtz International Center for FAIR" (HIC for FAIR) was accepted within the LOEWE Excellence Program. HIC for FAIR constitutes the think-tank for forefront theoretical and experimental research for the international Facility for Antiproton and Ion Research (FAIR). Our group is contributing a research project on QCD-based ab-initio nuclear structure theory supporting the experimental activities of the NuSTAR collaboration.