Theoretical
Nuclear Physics ++

 
Prof. Dr. Robert Roth
Institut für Kernphysik - Theoriezentrum
Schlossgartenstr. 2 - Gebäude S211
 
Welcome to the TNP++ web site. You will find information about the group, our research program, our teaching activities, and much more on these pages.
        
  • 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.
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